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o-Nitrobenzyl (oNB) derivatives are widely used photolabile caged compounds in chemical and biological applications. The primary step in the photoinduced deprotection is an excited state intramolecular hydrogen transfer (ESIHT) leading to tautomerization of the oNB compound and subsequent release of the protecting group. The prototype molecule for studying such ESIHT is o-nitrotoluene (oNT), where hydrogen transfers from the methyl to the nitro group. Using the complete active space self-consistent field (CASSCF) method with second-order perturbative energy corrections (CASPT2), we have comprehensively investigated the photoisomerization and photo decay mechanisms in oNT. We have obtained the minimum energy crossing points (MECPs) between relevant electronic states and identified the singlet and triplet pathways. There is a barrierless path for oNT to relax to the lowest triplet state. In this T1 state, the ESIHT products are more stable than T1 oNT. Hydrogen-transfer occurs on the T1 state followed by relaxation to the ground state to give the isomerized product. A biradical intermediate proposed by previous studies is characterized to be the hydrogen-transferred T1 product. On the singlet pathway, in contrast to the triplet, the ground state tautomer is formed from the S1 oNT through a geometrically distant and energetically higher S1/S0 conical intersection. Although nonadiabatic dynamical studies are essential for determining branching ratios, our study, which considers the accessibility of different MECPs based on geometry and energy, and the magnitude of spin-orbit coupling at singlet-triplet MECPs, suggests that a significant fraction of the isomerization yield is due to the triplet channel. [ABSTRACT FROM AUTHOR]

Amino acids constitute an important fraction of the water-soluble organic nitrogen (WSON) compounds in aerosols and are involved in many processes in the atmosphere. In this work, we applied X-ray photoelectron spectroscopy (XPS) to study aqueous solutions of four amino acids, glycine, alanine, valine, and methionine, in their zwitterionic forms. We found that amino acids with hydrophilic side chains and smaller size, GLY and ALA, tend to stay in the bulk of the liquid, while the hydrophobic and bigger amino acids, VAL and MET, are found to concentrate more on the surface. We found experimental evidence that the amino acids have preferential orientation relative to the surface, with the hydrophobic side chain being closer to the surface than the hydrophilic carboxylate group. The observed amino acid surface propensity has implications in atmospheric science as the surface interactions play a central role in cloud droplet formation, and they should be considered in climate models. [ABSTRACT FROM AUTHOR]

Herein, we report the enantioselective synthesis of a functionalized aza-octahydropentalene and its elaboration to a model tetracyclic core structure of calyciphylline B-type alkaloids. [ABSTRACT FROM AUTHOR]

High explosives that are photoactive, i.e., can be initiated with light, offer significant advantages in reduced potential for accidental electrical initiation. We examined a series of structurally related tetrazine based photoactive high explosive materials to detail their photochemical and photophysical properties. Using photobleaching infrared absorption, we determined quantum yields of photochemistry for nanosecond pulsed excitation at 355 and 532 nm. Changes in mass spectrometry during laser irradiation in vacuum measured the evolution of gaseous products. Fluorescence spectra, quantum yields, and lifetimes were measured to observe radiative channels of energy decay that compete with photochemistry. For the 6 materials studied, quantum yields of photochemistry ranged from <10-5 to 0.03 and quantum yield of fluorescence ranged from <10-3 to 0.33. In all cases, the photoexcitation nonradiatively relaxed primarily to heat, appropriate for supporting photothermal initiation processes. The photochemistry observed was dominated by ring scission of the tetrazine, but there was evidence of more extensive multistep reactions as well. [ABSTRACT FROM AUTHOR]

Catalytic aerobic oxidation of phenyl hydroxycarbamate 1 and 1-hydroxy-3-phenylurea 2 using CuCl2 and 2-ethyl-2-oxazoline in methanol gave acyl nitroso species in situ, which were trapped in nitroso-Diels–Alder (NDA) reactions with various dienes to afford the corresponding cycloadducts in high yields (90–98%). Competing ene products were also present for dienes containing both alkene π-bonds and allylic σ-bonds, and the ene yields are higher with 1 than with 2. The use of the chiral hydroxamic acid, (R)-1-hydroxy-3-(1-phenylethylurea) 3 (same conditions) gave NDA cycloadducts in high yields (97–99%) with no ene product from 2,3-dimethyl-1,3-butadiene. NDA cycloadducts were not obtained from other hydroxamic acid analogues [RCONHOH (R = PhCH24; Ph(CH2)25; Ph(CH2)36; Ph(CH2)47; Ph 8; 2-pyridyl 9; 3-pyridyl 10] with various dienes using copper-oxidation but rather were obtained using sodium periodate, resulting in variable NDA yields (13–51%) from hydroxamic acids 1–10 with cyclohexa-1,3-diene and 2,3-dimethyl-1,3-butadiene (several cycloadducts characterized by X-ray crystallography). The NDA and nitroso-ene reaction pathways of nitroso intermediates with dienes were mapped by DFT computations (B3LYP/6-31G*), which showed that the acyl nitroso species are super-reactive and that activation energies in the NDA processes are lower than the isomerization barriers between some cis- and trans-butadienes. [ABSTRACT FROM AUTHOR]

A direct N-trifluoromethylation method has been developed by the use of the in situ generated [ArICF3]+ species as the electrophilic trifluoromethyl source. Upon treatment of N-H ketimines with Ruppert-Prakash reagent in the presence of PhI(OAc)2 and KF, or with Togni's reagent II catalyzed by copper salt, N-trifluoromethylated imine products were obtained in moderate to good yields. [ABSTRACT FROM AUTHOR]

Silylative reduction of nitriles was studied under transition metal-free conditions by using B(C6F5)3 as a catalyst with hydrosilanes as a reductant. Alkyl and (hetero)aryl nitriles were efficiently converted to primary amines or imines under mild conditions. The choice of silanes was found to determine the selectivity: while a full reduction of nitriles was highly facile, the use of sterically bulky silanes allowed for the partial reduction leading to N-silylimines. [ABSTRACT FROM AUTHOR]

Highly diastereoselective and enantioselective reactions between 2-aroylvinylcinnamaldehydes and α,β-unsaturated imines were achieved under asymmetric catalysis of chiral triazole carbene catalysts. In the presence of N-anisylindeno[2,1-b]triazolo[4,3-d][1,4]oxazinium salt, the reaction of 2-aroylvinylcinnamaldehydes with α,β-unsaturated imines afforded indeno[2,1-c]pyran-1-one derivatives 4 with 90%-99% ee, while enantiopure indenocyclopentan-1-ones 5 (>99% ee) were obtained under the catalysis of N-mesitylindeno[2,1-b]triazolo[4,3-d][1,4]oxazinium salt. A slight variation of an N-substituent on triazole carbenes was found to switch completely the diastereoselectivity of the reaction for the formation of indeno[2,1-c]pyran-1-ones. [ABSTRACT FROM AUTHOR]

A strategy has been developed that culminated in a stereoselective total synthesis of the tetracyclic antimalarial Myrioneuron alkaloid myrioneurinol. The synthesis relies on three highly diastereoselective reactions, including an intramolecular chelation-controlled Michael spirocyclization of an N-Cbz-lactam titanium enolate to an α,β-unsaturated ester for construction of the A/D-ring system and the attendant C5 (quaternary), C6 relative stereochemistry; a malonate enolate conjugate addition to a nitrosoalkene in order to install the appropriate functionality and establish the configuration at C7; and an intramolecular aza-Sakurai reaction to form the B-ring and the accompanying C9 and C10 stereocenters. [ABSTRACT FROM AUTHOR]

A mild and efficient one-pot procedure is described to transform salicylaldoximes into salicylonitriles using Mitsunobu chemistry. The reactions proceed through the corresponding 1,2-benzisoxazoles that undergo the Kemp elimination in situ to generate the target salicylonitriles in excellent yields. The chemistry exhibits a broad scope, and the salicylonitriles can be readily isolated by a simple acid-base workup. In addition to functioning as useful synthetic precursors, salicylonitriles may serve as more cell penetrable bioisosteres of carboxylic acids. [ABSTRACT FROM AUTHOR]

The asymmetric total synthesis of (-)-14,15-dihydrosecurinine and the formal total synthesis of (-)-securinine were accomplished starting from an easily available malimide. A concise SmI2-mediated radical coupling strategy has been developed to construct the bridged α-hydroxy 6-azabicyclo[3.2.1]octanone in four steps with high diastereoselectivity. [ABSTRACT FROM AUTHOR]

In the present work, the combinedelectronic structure calculationsand dynamics simulations have been performed to explore the decompositionreactions of 2H-azirine, 2-phenyl-2H-azirine, and 3-phenyl-2H-azirine in gas phase.Thermal cleavage of the C–C single bond yields nitrile ylidesas products with a high barrier (>50.0 kcal mol–1). On the other hand, photochemical cleavage reactions starting fromthe 1nπ* state of 2H-azirine and3-phenyl-2H-azirine are ultrafast nonadiabatic processes(<100 fs), leading to nitrile ylides through the S1/S0conical intersection. The fast formation of ylides in experimentswas well reproduced by present dynamics simulations. For 3-phenyl-2H-azirine, population of the S1(1ππ*)state is another decay pathway for the S2(1nπ*)state. The C–N bond cleavage upon photoexcitation was usuallyconsidered to take place in T1state. However, our calculationsreveal that photocleavage of the C–N single bond for 2-phenyl-2H-azirine is very likely to take place in S1state.The present work provides new insights into photocleavage mechanismof 2H-azirine and the related derivatives. [ABSTRACT FROM AUTHOR]

The direct addition of anionic secondary phosphine boranes to carbodiimides yields both chiral and achiral phosphaguanidine boranes under ambient temperature conditions. An analogous preparation of menthol-derived phosphinite boranes is also described. These products can be deborinated to give the corresponding phosphines, and subsequently oxidized to give phosphine oxides. The robustness of this method was further demonstrated in the synthesis of structurally novel cyclic phosphaguanidines. [ABSTRACT FROM AUTHOR]

Phosphonylated pyrroles were obtained by a ZnCl2-catalyzed 5-exo-dig hydroamination of propargylic enamines. These starting compounds were obtained in two steps from commercially available β-ketophosphonates. The method tolerates a wide variety of substituents at the 1,2- and 5-position of the pyrrole, while further derivatization allows for the introduction of substituents at the 4-position via lithiation or halogenation. [ABSTRACT FROM AUTHOR]

A methyl 2-trifluoromethyl-2-sHoxycydopropanecarboxylate was smoothly deprotonated by lithium diisopropy-lamide and reacted with carbon disulfide and methyl iodide to afford a dihydrothiophene derivative. The crucial step in this transformation is a ring-expansion of the anionic intermediate by [1,3] sigmatropic rearrangement. The dihydrothiophene was converted into the corresponding 5-trifluoromethylthiophene derivative by phosphoryl chloride in refluxing pyridine. A one-pot version of the reaction sequence efficiently provided the thiophene in good yield. Analogously, aryl- and alkyl-substituted isothiocyanates instead of carbon disulfide afforded the corresponding trifluoromethyl-substituted pyrroles in moderate to very good overall yields. Explorative reactivity studies with the methylthio-substituted thiophene and pyrrole derivatives demonstrate that they are precursors of a range of interesting trifluoromethyl-substituted products, including new members from the thienothiophene and thienopyrrole class. [ABSTRACT FROM AUTHOR]

Structures and properties of nitrile imines were investigated computationally at B3LYP and CCSD(T) levels. Whereas NBO analysis at the B3LYP DFT level invariably predicts a propargylic electronic structure, CCSD(T) calculations permit a clear distinction between propargylic, allenic, and carbenic structures. Nitrile imines with strong IR absorptions above ca. 2150 cm-1 have propargylic structures with a CN triple bond (RCNNSiMe3 and R2BCNNBR2), and those with IR absorptions below ca. 2150 cm-1 are allenic (HCNNH, PhCNNH, and HCNNPh). Nitrile imines lacking significant cumulenic IR absorptions at 1900-2200 cm-1 are carbenic (R-(C:)-N=N-R'). Electronegative but lone pair-donating groups NR2, OR, and F stabilize the carbenic form of nitrile imines in the same way they stabilize "normal" singlet carbenes, including N-heterocyclic carbenes. NBO analyses at the CCSD(T) level confirm the classification into propargylic, allenic, and carbenic reactivity types. Carbenic nitrile imines are predicted to form azoketenes 21 with CO, to form [2+2] and [2+4] cycloadducts and borane adducts, and to cyclize to 1H-diazirenes of the type 24 in mildly exothermic reactions with activation energies in the range 29-38 kcal/mol. Such reactions will be readily accessible photochemically and thermally, e.g., under the conditions of matrix photolysis and flash vacuum thermolysis. [ABSTRACT FROM AUTHOR]

Imines and carboxylic acids have been directly coupled using propylphosphonic acid anhydride and NEt(i-Pr)2 to give N-acyliminium ions, which were intramolecularly trapped with oxygen, nitrogen, sulfur, and carbon nucleophiles to provide a wide range of structurally diverse heterocycles. [ABSTRACT FROM AUTHOR]

The synthesis of 3,4-dihydro-1,2-oxazepin-5(2H)-ones and 2,3-dihydropyridin-4(1H)-ones from β-substituted β-hydroxyaminoaldehydes is reported. The β-hydroxyaminoaldehydes were prepared by enantioselective organocatalytic 1,4-addition of N-tert-butyl (tert-butyldimethylsilyl)oxycarbamate to α,β-unsaturated aldehydes (MacMillan protocol). Alkyne addition to the aldehydes followed by alcohol oxidation furnished N-Boc O-TBS-protected β-aminoynones. Removal of the TBS protecting group initiated a 7-endo-dig cyclization to yield previously unknown 3,4-dihydro-1,2-oxazepin-5(2H)-ones. Reductive cleavage of the N-O bond of the oxazepinones and Boc-deprotection provided 2-substituted 2,3-dihydropyridin-4(1H)-ones via 6-endo-trig cyclization. 2,3-Dihydropyridin-4(1H)-ones are versatile intermediates that have been used for the synthesis of many alkaloids. The new protocol allows the synthesis of 3-dihydropyridin-4(1H)-ones carrying an array of substituents at C2 that cannot be prepared from commercial β-amino acids or by one-carbon homologation of proteinogenic amino acids. The use of readily available β-hydroxylaminoaldehydes expands the utility of our previously reported method to prepare 2,3-dihydropyridin-4(1H)-ones from β-amino acids as the source of diversity and chirality. A broad substrate scope is possible because β-aminoaldehydes can be prepared from α,β-unsaturated aldehydes by an enantioselective organocatalytic process. [ABSTRACT FROM AUTHOR]

Cross-coupling reactions involving metal-carbene are emerging as a new type of carbon-carbon bond-forming reaction. The aim of this JOCSynopsis is to provide an overview of the most recent development of these reactions, focusing on the use of diazo compounds (or in situ formed diazo compounds from N-tosylhydrazones) as carbene precursors. In addition, the integration of this type of reaction with C-H bond functionalization is also surveyed. [ABSTRACT FROM AUTHOR]

The mechanism of the chiral VANOL-BOROX Brønsted acid catalyzed aziridination reaction of imines and ethyldiazoacetate has been studied using a combination of experimental kinetic isotope effects and theoretical calculations. A stepwise mechanism where reversible formation of a diazonium ion intermediate precedes rate-limiting ring closure to form the cis-aziridine is implicated. A revised model for the origin of enantio- and diastereoselectivity is proposed based on relative energies of the ring-closing transition structures. [ABSTRACT FROM AUTHOR]

Two types of rearrangements have been investigated computationally at the B3LYP/6-311+G(d,p) level. The activation barriers for rearrangement of acyl thiocyanates RCO-SCN to the corresponding isothiocyanates RCO-NCS are 30-31 kcal/mol in agreement with the observation that the thiocyanates are in some cases isolable albeit very sensitive compounds. Alkoxycarbonyl-, (alkylthio)carbonyl- and carbamoyl thiocyanates are isolable and have higher calculated barriers (ca. 40 kcal/mol) toward rearrangement to isothiocyanates, whereas all thioacyl thiocyanate derivatives are rather unstable compounds with barriers in the range 20-30 kcal/mol for rearrangement to the isothiocyanates. Acyl-, alkoxycarbonyl-, and carbamoyl cyanates R-CO-OCN are predicted to be in some cases isolable compounds with barriers up to ca. 40 kcal/mol for rearrangement to the isocyanates RCO-NCO. All of the rearrangements of this type involve the HOMO of a nearly linear (thio)cyanate anion and the LUMO of the acyl cation, in particular the acyl C=X π* orbital. The second type of rearrangement involves 1,3-shifts of the groups R attached to the (thio)acyl groups, that is, acyl isothiocyanate-thioacyl isocyanate and imidoyl isothiocyanate-thioacyl carbodiimide rearrangements. These reactions involve four-membered cyclic, zwitterionic transition states facilitated by lone pair-LUMO interactions between the migrating R group and the neighboring iso(thio)cyanate function. Combination of the two rearrangements leads to the general reaction scheme RCX-YCN ⇌ RCX-NCY ⇌ RCY-NCX ⇌ RCY-XCN (X and Y = O, S, NR'). [ABSTRACT FROM AUTHOR]

The amphimedosides, discovered in 2006, are the first examples of naturally occurring glycosylated alkoxyamines. We report syntheses of amphimedosides A-C that feature a stereoselective oxyamine neoglycosyiation and found that these alkaloids display modest cytotoxicity toward seven diverse human cancer cell lines, exhibiting IC50 values ranging from 3.0 µM to greater than 100 µM. [ABSTRACT FROM AUTHOR]

This report describes the synthesis of 4-organoselenylisoxazoles via FeCl3/RSeSeR-mediated intramolecular cyclization of alkynone O-methyloximes. The optimized conditions allowed the cyclization to proceed at room temperature under ambient atmosphere, and the reaction requires a short time to be completed. The reaction conditions tolerated neutral, electron-donating and electron-withdrawing groups present in both substrates, alkynone O-methyloximes and diorganyl diselenides. Treatment of 4-organoselenylisoxazoles with n-butyllithium, followed by trapping with electrophiles, furnished the functionalized isoxazoles in good yields. The obtained products also proved to be suitable substrates for the preparation of 4-bromoisoxazoles via Br/Se exchange reaction. [ABSTRACT FROM AUTHOR]

The conjugate addition of lithium (R)-N-(3-chloropropyl)-N-(α- methylbenzyl)amide to α/β-unsaturated esters was used as the key step in the syntheses of all possible diastereoisomers of the homalium alkaloids hoprominol and hopromalinol. Comparison of the specific rotation data for these synthetic samples with those of samples isolated from the natural source enabled the absolute configurations within these alkaloids to be confidently assigned for the first time as (-)-(R,R,R)-hoprominol and (-)-(4'S,4"R,2"R)-hopromalinol. The asymmetric syntheses of (-)-(R,R,R)-hoprominol (in 10 steps and 4.0% overall yield) and (-)-(4'S,4"R,2"R)-hopromalinol (in 10 steps and 9.3% overall yield), from commercially available starting materials in each case, therefore represent the first total asymmetric syntheses of these alkaloids to be reported. [ABSTRACT FROM AUTHOR]

A stereochemically controlled route to the enantiopure [6-6-5-7] tetracyclic core of Calyciphylline A class alkaloids was established, which involves Overman rearrangement, [2 + 2] photochemical cycloaddition, Grob fragmentation, C-N bond-forming nucleophilic displacement, and ring strain-directed hydrogenation as strategic steps. [ABSTRACT FROM AUTHOR]

A novel palladium-catalyzed cascade allylic amination/intramolecular hydroamination/isomerization process of protected enynol 1 and primary amine 2 has been explored, which constructs the important 1,2,5-trisubstituted pyrroles. This transformation offers an alternative synthetic methodology capable of generating substituted pyrroles in a straightforward way. [ABSTRACT FROM AUTHOR]

A series of 1-aryl/alkyl-1H-1,2,3,4-tetrazoles, 5-substituted 1H-tetrazoles, and 1,5- and 2,5-disubstituted 1H-tetrazoles were studied by a combination of experimental NMR (natural abundance 15N, 15N/¹H HMBC, and 13C) and computational GIAO-NMR techniques to explore substituent effects on 15N (and 13C) NMR chemical shifts in the tetrazole (TA) moiety. Computed 15N chemical shifts via GIAO-B3LYP/6-311+G(2d,p) calculations gave satisfactory results in comparison with experimental data. Whereas N-alkylation leads to large 15N chemical shift changes, changes in the N1-aryl derivatives bearing diverse substituent(s) are generally small except for polar ortho-substituents (COOH, NO2). Large Δδ15N values were computed in N1-aryl derivatives for p-COH2+ and p-OMeH+ as extreme examples of electron-withdrawing substituents on a TA moiety. [ABSTRACT FROM AUTHOR]

We have disclosed a general and efficient synthetic strategy for polysubstituted pyridines and isoquinolines with high chemo- and regioselectivity. In this methodology, 1-alkynyl imines act as the key compound to undergo a sequential alkynyl imine--allenyl imine isomerization/aza-Diels--Alder reaction/aromatization. In the first place, 1-alkynyl imines were formed in situ by a highly selective multicomponent reaction of isocyanides, arynes, and terminal alkynes and reacted with another molecule of arynes or terminal alkynes to furnish target heterocyclic products in a highly efficient and atom-economic manner. On the other hand, we attempted to prepare 1-alkynyl imines by other approaches to undergo a similar reaction sequence to afford polysubstituted pyridines and isoquinolines with a wider range. Different from the first approach, the second approach utilized the preprepared 1-alkynyl imines to introduce the related different substitutents into the final products: arynes or terminal alkynes bearing substituents different from those of 1-alkynyl imines have been successfully applied for the synthesis a wide variety of pyridines and isoquinolines with diversity. [ABSTRACT FROM AUTHOR]

A systematic exploration of thiophilic ability of o-iodoxybenzoic acid (IBX) for oxidative desulfurization to trigger domino reactions leading to new methodologies for synthesis of different azoles is described. A variety of highly substituted oxadiazoles, thiadiazoles, triazoles, and tetrazoles have been successfully synthesized in good to excellent yields, starting from readily accessible thiosemicarbazides, bis-diarylthiourea, 1,3-disubtituted thiourea, and thioamides. [ABSTRACT FROM AUTHOR]

Phenylselenyl benzylcarbanion stabilized by an (S)-2-p-tolylsulfinyl group evolves in a highly stereoselective way in the reaction with (S)-N-(p-tolylsufinyl)imines at -98 °C affording diastereomerically pure 1,2-selenoamino derivatives in good yields. The syn or anti relationship of the obtained compounds depends on the alkyl or aryl character of the imine. They are easily transformed into enantiomerically pure (1R,2S)-1-aryl[or (1S,2S)-1-alkyl]-2-(phenylseleno)-2-phenylethylamines by reaction with t-BuLi and subsequent methanolysis of the generated sulfinamide derivatives with TFA. [ABSTRACT FROM AUTHOR]

An approach to the synthesis of 1-alkyl-5-((di)alkylamino)tetrazoles by nucleophilic substitution in 1-alkyl-5-sulfonyltetrazoles with anions generated from the primary or secondary amines was developed. Tolerance of the method to the presence of some functional groups (i.e., protected amine) in both components of the reaction was demonstrated. Obtained tetrazoles are promising building blocks for the design of peptide surrogates, in particular, for replacement approaches of alkyl urea derivatives. [ABSTRACT FROM AUTHOR]

A simple and efficient route for the synthesis of 5-substituted 1H-tetrazoles catalyzed by CoY zeolite is reported. The salient features of this atom-economical, cost-effective, and high-yield cobalt-catalyzed protocol are aerobic conditions, lower reaction time, and milder reaction conditions without additives. Other advantages include experimental ease of manipulation, safer alternative to hazardous, corrosive, and polluting conventional Lewis acid catalysts, recovery, and reusability with consistent catalytic activity. The results are rationalized by proposing a suitable mechanism. [ABSTRACT FROM AUTHOR]

Palladium-catalyzed asymmetric allylic etherizations with a variety of oximes as nucleophiles utilizing a chiral alkene-phosphine hybrid ligand have been successfully achieved for the first time to afford the optical active oxime ethers in high yields with good to excellent enantioselectivities. [ABSTRACT FROM AUTHOR]

Two new polyhydroxylated nortropane analogues closely related with Calystegines have been prepared in excellent chemical yields and complete selectivity. A synthetic strategy based on consecutive nucleophilic allylation, oxidation, and intramolecular dipolar cycloaddition was developed. The formation of key intermediate cycloadducts were observed to take place through the recently confirmed thermally induceded 2-aza-Cope rearrangement of nitrones. [ABSTRACT FROM AUTHOR]

Addition of hydroxylamine to substituted 4-chlorobutanals gives intermediate nitrones that undergo tandem cyclization and then intramolecular dipolar cycloaddition to give the core ring system of the yuzurimine-type natural products. Ring-opening of the isoxazolidines gives amino alcohols that can be converted to 1,3-oxazines, representing the tetracyclic core of alkaloids such as daphcalycic acid and daphcalycine. [ABSTRACT FROM AUTHOR]

Novel helical macrocyclic imines derived from planar chiral [2.2]paracyclophane were synthesized. The chiroptical properties of the enantiopure compounds were investigated and their absolute configurations were assigned. [ABSTRACT FROM AUTHOR]

The asymmetric catalytic aziridination reaction (AZ reaction) of imines derived from dianisylmethyl (DAM) amine and tetra-methyldianisylmethyl (MEDAM) amine were examined with boroxinate catalysts prepared from both the VANOL and VAPOL ligands. This included an evaluation of different protocols for the preparation of the catalyst. The AZ reaction of DAM and MEDAM imines prepared from nine different aryl and aliphatic aldehydes were examined. The MEDAM imines were superior to the DAM imines in the AZ reaction, giving much higher asymmetric inductions and higher overall yields of aziridines. The MEDAM imines were found to also be superior to the previously studied diphenylmethyl (benzhydryl or Bh) and tetra-zerl-butyldianisylmethyl (BUDAM) imines especially for imines derived from aliphatic aldehydes. The average asymmetric induction over the nine different MEDAM imines studied was 97% cc with the VAPOL catalyst and 96% cc with the VANOL catalyst. The MEDAM imines can be deprotected to give N-H aziridines in all cases except for some electron-rich aryl aldehydes. The MEDAM imines are much more reactive than benzhydryl imines, and this was most evident when a diazoacetate ester is replaced by a diazoacetamide. The less reactive diazoacetamides give very low yields in their reactions with benzhydryl imines but high yields with MEDAM imines. [ABSTRACT FROM AUTHOR]

Two new bisindole alkaloids, bisnicalaterines B and C (1 and 2) consisting of an eburnane and a corynanthe type of skeletons, were isolated from the bark of Hunteria zeylanica. Their absolute structures were determined by combination of NMR, CD, and computational methods, and each of them was shown to be in an atropisomeric relationship. Bisnicalaterines B and C (1 and 2) showed potent vasorelaxant activity on isolated rat aorta. [ABSTRACT FROM AUTHOR]

The Rh(I)-catalyzed addition of alkenyl and aryl MIDA boronates to N-tert-butanesulfinyl aromatic and aliphatic imines proceeds in good yields (up to 99%) and with very high selectivity (98:2 to > 99:1). In comparison to trifluoro- borates, higher yields and selectivities are observed for the addition to N-terf-butanesulfinyl aromatic imines. This new method expands upon the versatility of the Rh(I)- catalyzed addition of boron reagents to imines, thereby further enabling the synthesis of chiral α-branched amines. [ABSTRACT FROM AUTHOR]

An atom-economical phosphane-free palladium-catalyzed direct C-2 arylation of unactivated free NH-pyrroles is devised. This method provides a straithforward route to a wide variety of substituted 2-arylI H-pyrroles from readily accessible starting materials. lodoarenes bearing electron-withdrawing and electron-donating substituents are tolerated under the presented reaction conditions. The scope of the reaction is also expanded to N-aryl and -alkylpyrroles albeit in lower yields. [ABSTRACT FROM AUTHOR]

Chemoselective formation of glycoconjugates from unprotected glycans is needed to further develop chemical biology involving glycans. Carbohydrate oxime formation is often slow, and organocatalysis by anilines would be highly promising. Here, we present that carbohydrate oxime formation can be catalyzed with up to 20-fold increases in overall reaction rate at 100 mM aniline. Application of this methodology provided access to complex glycoconjugates. [ABSTRACT FROM AUTHOR]

Two unnatural alkaloids were observed for the first time while attempting to initiate a plausibly biomimctic cyclization approaching to (-)-lycojapodinc A, one of the newest Lycopodiuni alkaloids. [ABSTRACT FROM AUTHOR]

A flexible method for the diastereoselective total synthesis of the pyrrolizidine alkaloids uniflorine A, casuarine, australine, and 3-epi-australine and the unnatural epimer 3,7-di-epi-australine from a common chiral 2,5-dihydropyrrole precursor is described. [ABSTRACT FROM AUTHOR]

Photoelectron imaging probes both molecular electronic structure and electron molecule interactions. In the current work images were recorded for detachment from the I−·C4H5N (I−·pyrrole) cluster anion at wavelengths between 360 and 260 nm. The direct detachment spectra show strong similarities to those of I−, although a strong solvent shift, broadening and some structure is observed. A nondirect, dissociative or autodetachment feature is also observed over a range of wavelengths. Ab initio calculations identify several local minima associated with neutral and anion isomers. Energy and Franck−Condon arguments are used to assess the role of these in the detachment process. The cluster anion structure is essentially an I−atomic anion in the presence of a neutral pyrrole molecule. The spectral structure arises due to interactions in the open shell neutral cluster residue resulting from detachment. The indirect detachment feature arises through the formation of an intermediate dipole bound cluster anion state which subsequently dissociates. The energy dependence of this channel (observed over a 0.6 eV range of photon energies) is discussed in terms of the wide amplitude motions associated with the van der Waals modes of the cluster anions. [ABSTRACT FROM AUTHOR]

Lewis base catalyzed reactions of N-Boc-imines and ethyl 2,3-butadienoate were investigated systematically. The normal aza-Morita—Bylis—Hillman products were obtained in good to excellent yields catalyzed by DABCO. When PPh3 was used as the catalyst, novel rearrangement product (E)-ethyl 2-((Z)-(lert-butoxycarbonylimino)- (aryl)methyl)but-2-enoates could be formed in moderate yields. [ABSTRACT FROM AUTHOR]

An organocatalyzed approach to enantioenriched isoquinuclidines and bicyclo[2.2.2]octanes via a p-dodecylphenylsulfonamide-modified proline catalyst has been developed. A series of aromatic imines have been explored for the formation of isoquinuclidines with high levels ofenantioselectivity and diastereoselectivity, strongly favoring the exo product. A series of aliphatic imines has also been explored, which provide access to bicyclo[2.2.2loctanes through a novel mechanistic pathway in high levels of enantioselectivity and diastereoselectivity, favoring the endo product. [ABSTRACT FROM AUTHOR]

Ethyl cyanoformate exists as a mixture of two conformers but displays three R-branch a-type band series in its rotational spectrum. Simulations with population fractions 0.37 at 210 K and 0.70 at 297 K undergoing conformer exchange with average conformer lifetimes, ⟨τiso⟩, shorter than ∼40 ps at ∼210 K and shorter than ∼37 ps at 297 K reproduce the experimental spectra between 26.5 and 38 GHz, the exchanging species accounting for the third set of bands. The upper-limit ⟨τiso⟩’s are 1 order of magnitude longer than RRKM theory predictions and the population fractions are consistent with the total population with energy above 700 cm−1, approximately twice the conformer interconversion barrier height. Model calculations indicate that extensive K-sublevel mixing in individual molecular eigenstates can produce the large population and the narrow distribution of the rotational-constant sum, B+ C, consistent with the observed exchange-averaged band series. [ABSTRACT FROM AUTHOR]

ortho-Lithiophenyl (-hetaryl) isocyanides react with aldehydes and ketones providing isocyanoalcohols 8 (36-89%, nine examples), 4H-3,1-benzoxazines 9 (45-78%, six examples) or, after two types of rearrangements, isobenzofuran-1(3H)-imines (iminophthalanes) 18 (52-75%, four examples), or indolin-2-ones 19 (42-79%, two examples), depending on the reaction conditions and substitution patterns. Isocyanoalcohols 8, in turn, were converted to 9 or 18 under Cu(I) catalysis (66-86%, eight examples). 4H-3, 1 -Benzoxazin-4-ones 39-Nu and isatoic anhydride 40 were obtained by the reaction of 2 with carbon dioxide followed by trapping of the lithiated intermediate with iodine and subsequent reactions with nucleophiles (45-60%, three examples). [ABSTRACT FROM AUTHOR]

Addition of Grignard reagents to chiral imines derived from isatine afforded chiral, optically enriched 3-substituted 3-aminooxindoles in satisfactory yields and diastereoisomeric ratios. A general protocol is described for the addition Of alkyl, alkenyl, and aryl Grignard reagents. In one case, the absolute configuration at C3 was determined and the selective N-deprotection was described, enabling further synthetic transformations of the reaction product. [ABSTRACT FROM AUTHOR]

The first transition-metal-free addition of alkyl nitriles to unactivated imines was developed using a catalytic combina- tion of 4-MeOC6H4ONa and TMSCH2CO2Et to promote the reaction. The corresponding β-amino nitriles are obtained in good to almost quantitative isolated yields under mild conditions. A mechanism involving an autocatalytic pathway is proposed on the basis of experimental observations. [ABSTRACT FROM AUTHOR]