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The reaction of BOC2O in the presence and absence of DMAP was examined with some amines, alcohols, diols, amino alcohols, and aminothiols. Often, unusual products were observed depending on the ratio of reagents, reaction time, polarity of solvent, pKa of alcohols, or type of amine (primary or secondary). In reactions of aliphatic alcohols with BOC2O/DMAP, we isolated for the first time carbonic-carbonic anhydride intermediates; this helps explain the formation of symmetrical carbonates in addition to the O-BOC products. In the case of secondary amines, we succeeded to isolate unstable carbamic-carbonic anhydride intermediates that in the presence of DMAP led to the final N-BOC product. The effect of N-methylimidazole in place of DMAP was also examined.

Reaction of RuCl2(PPh3)3 with the bisphosphine {1,3,5-(CH3)3-2,6-(iPr2PCH2)2C6H} (1) under 30 psi H2 results in quantitative C−C activation of an Ar−CH3 bond to afford Ru(Cl)(PPh3){2,6-(iPr2PCH2)2-3,5-(CH3)2C6H} (2) and CH4, whereas reaction of RuCl2(PPh3)3 with 1 in the presence of NaOtBu results in selective ArCH2−H bond activation to afford the benzylic complex Ru(Cl)(PPh3){1-CH2-2,6-(iPr2PCH2)2-3,5-(CH3)2C6H} (7). The identity of the 16-electron complex 2 was confirmed by reaction of the bisphosphine {2,6-(iPr2PCH2)2-3,5-(CH3)2C6H2} (3), lacking the Ar−CH3 group between the phosphine arms, with RuCl2(PPh3)3. Metal insertion into an Ar−Et bond was observed as well. Follow-up of the reaction of RuHCl(PPh3)3 with 1 by NMR and deuterium labeling studies reveal that the kinetic products of ArCH2−H bond activation (7 and H2) are irreversibly converted into the thermodynamically more stable products of Ar−C bond activation (2 and CH4) via reversal of the C−H activation process. Reaction of (COD)PtCl2 (COD = ...

Branched-chain five-membered ring aza-sugar analogues, synthesized from amino acids by an intramolecular oxime−olefin cycloaddition reaction, the IOOC route, were found to be selective glycosidase inhibitors. The derivative 2,4(S)-di(hydroxymethyl)-3(S)-aminopyrrolidine, obtained from d-serine, was about 1 order of potency more active than its enantiomer obtained from l-serine.

Reaction of 2-chlorooxabicyclo[4.2.0]octanone 5 with several nucleophiles was examined and found to differ significantly from those of carbon analog 1. MeO(-) and PhS(-) led either to products of cine substitution 9 or of ring opening to cyclobutenones 8. With most enolates cine substitution occured via C-alkylation of the intermediate oxidoallyl cation in spite of formation of a new C-C bond between two quaternary carbons; with nitroalkanes O-alkylation was preferred. With azide as a nucleophile, further transformations occurred, among them an oxy-promoted electrocyclic cyclobutane opening, with incorporation of a phenyl triazole unit and final formation of the unusual product 19a. Evidence for a mechanism explaining formation of 19a was obtained by isolation of intermediates. Thermolysis or photolysis of 8e or9b led via electrocyclic ring opening to a vinyl ketene which was trapped by MeOH, alkenes, dienes, or oxygen to produce polyfunctional unsaturated esters 29 and 30 or 8-membered ring lactone 31, fused cyclobutanones 33 and 34, pyranone 38, or gamma-lactone 39, respectively.

The nitrogen inversion barriers for N-isopropyl-, N-butyl-, N-isobutyl-, and N-tert-butyl-7-azabicyclo[2.2.1]heptanes were measured using dynamic NMR line shape analysis. These barriers as well as ...

The [3 + 2] cyclopentanation involving 3-(phenylsulfonyl)-2-(bromomethyl)-1-propene (1) and representative (E) α,β-unsaturated acyclic esters and ketones has been studied. High yields and complete stereoselectivity were observed in all reactions leading to tri- or tetrasubstituted methylenecyclopentanes. The anti-diastereoselectivity in the first, Michael addition step is rationalized by a chelation-controlled transition state in which MO interactions of the two π systems are involved. The Michael reactions of methallyl sulfone 8 with (E) enoates in the absence and presence of HMPA confirms the influence of chelation on the diastereomeric ratio of adducts. Cyclopentanations involving 1 with cyclohexenone, 2(5H)-furanone, and 5,6-dihydro-2-pyranone, respectively, were also studied with emphasis on the factors influencing the stereochemical outcome of the annulation process.

Reactions of 1-(phenylsulfonyl)-2-methylene-3-bromopropane (1) with various nitroolefins have been investigated with the purpose of devising a tandem [3+2]-annulation leading to nitro-substituted derivatives of methylenecyclopentanes. The conjugate addition step occurred readily affording 4a-e (syn) and 5a-e (anti) adducts. The anti-adducts cyclized further in the presence of HMPA to give stereoisomeric methylenecyclopentane derivatives 6a-f and 1a-f. At higher reaction temperature, partial ring closure of 4a-d-syn isomers to give cis-2,3-disubstituted cyclopentanes 8a-d could also be achieved. Base-induced equilibration provided in a one-vessel operation, starting from 1 and 1-nitrobutene (3b), the methylenecyclopentane 6b with three stereogenic centers

Thermal intramolecular oxime olefin cycloaddition of α-allylamino aldoximes and ketoximes 4 led stereospecifically to formation of oxadiazabicyclo[3.3.0]octanes 6. The presence of heteroatoms in these bicyclic fused 5-membered rings permits for the first time an evaluation of the conformation of this system by means of NMR. We found that some substituents in 6 restrict the conformational mobility of these five-membered rings to the extent that only one conformer was detected at 20 o C. In other cases an equilibrium between two major conformers was revealed by NMR. Equilibrium measurements indicated a free energy of conversion of 13.2-13.4 kcal/mol, apparently a manifestation of the N-inversion in the isoxazolidine ring. NMR studies also showed that the NH-proton in isoxazolidines 6 prefers an axial orientation. Empirical force field data were adjusted for MM calculations in these bicyclic heterocycles. The MM2 force field with AMBER charge gave the best fit between calculated and experimental coupling constants

The furan-fused chlorocyclobutanone 6 undergoes reaction with O, N, S, C nucleophiles at a much slower rate than its pyran homolog, which is attributed to a reluctance to enolization. Instead of subsititution products, rearranged products were formed.Enolization of 6 (6=chlorooxabicyclo[3.2.0]heptanone)toward the ring jonction in the oxabicycloheptanone is greatly retarded compared to the oxabicyclooctanone and proceeds only with strong nucleophiles(MeO - , - CH(COOEt) 2 at 20°C or with N 3 - on heating).The cine substitution products were not isolated but underwent further transformations;with oxygen nucleophiles such as AcO - or HO - ,when heating was required, the products were seven- or five- membered-ring lactones.These were formed either via vinylketenes or by opening of the cyclobutanone and/or the tetrahydrofuran ring.PhS - gave an ipso substitution product (presumably via electron transfer) that underwent acid-catalysed rearrangement to a naphtofuran

Reaction of 2-(4'-bromobutyl)-5-ethoxyxazole (1) with nucleophiles led either to S N 2 substitution products or to products with a piperidine skeleton. The latter were shown to arise from an intramolecular ring closure to an oxazolium salt 7, wich was faster in the presence of a catalytic amount of Nal and in a polar solvent and fro which NMR evidence is presented. The further transformation of 7 tyo 3-6 apparently involves addition of nucleophiles to 7 to produce 4-oxazoline 8 which opens to azomethine ylide 9

Chlorobycyclooctanone 3 on reactin with H 2 O-Et 3 N in acethonitrile at 20 o C produced in high yield four complex dimeric compounds 4-7. The novel structures produced by C-C bond formation between tertiary centers were revealed by NMR and X-ray diffraction. Pathways leading from 4 or its diastereomer 14 to cage compounds 5-7 indicate the importance of proximity effects in these transformations

We report the first examples of intramolecular Diels-Alder addition of heterodienophiles N=N, C=N, C=O, C=S to oxazoles. The required 5-ethoxy- and 5-phenyloxazoles were synthesized bearing a side chain of variable length on C-2 to which the different heterodienophiles are attached. The products of the thermal bis heteroannulation are 3-triazolines, imidazolines, oxazolines, or thiazolines fused to a five- to six-membered ring. Relative reactivities were established and the mechanism is discussed

The intramolecular oxime olefin cycloaddition (IOOC) of proline and pipecolinic acid derivatives proceeds thermally with a high degree of stereoselectivity to provide a new route to functionalized pyrrolizidines, indolizidines, or quinolizidines. The ring closure proceeds with simultaneous stereoselective introduction of three or four stereocenters. Molecular mechanics calculations have been refined to accurately predict not only which stereoisomer is preferred but also the syn and anti coupling constants in these tricyclic molecules

A two-step sequence is described for conversion of cyclic and acyclic ketone enolates into α-methylenevalerolactones. The first step involves Michael addition to ethyl α-((phenylsulfony)methyl)acrylate 1 with concomitant elimination of PhSO 2 and formation of unsaturated keto esters 2-7. In the next sequence chemoselective ketone reduction is usually followed by spontaneous lactonization of acidification. Contrary to the five- and six-membered ring systems, the cis-fused isomer predominates in the seven- and eight- membered ring compounds 12 and 13. Spiro α-methylenevalerolactones 17a,b are as well obtainable by a short sequence of steps from 2-oxocyclohexanecarboxylate and 1

Nitriles are shown to react with C, N-diacylimines 2, generated in situ from 1 or 4 in the presence of Lewis acids, to produce 4-amidooxazoles 5 and 6 in good to excellent yield. Diamides are sometimes also produced. The reaction was followed by NMR spectroscopy, and mechanistic pathways are discussed

The strained keto diol 5 underwent an unexpected rearrangement in the presence of H 2 O-TEA-CH 3 CN at 20 o C to afford two isomeric product 6 and 7. The latter two compounds undergo further conversion to carboxy keto diol 8. The structures of 6-8 were elucidated by heterero COSY experiments and in the case of 6 by X-ray diffraction. The transformation of 5 to 6 and 7 is interpreted as involving an unusual retroaddition of a benzylic anion to a cyclobutanone 5→10. This is facilitated by subsequent readdition of this anion to another proximally located ketone with formation of a cyclopropanol 11, which is immediately converted to 6 and 7

The use of a polymeric azidation reagent for the preparation of explosive azidomethanes at ambient temperature is described. Thus, methyl iodide was converted into methyl azide, methylene bromide and methylene chloride into diazido methane, and bromoform into triazido methane. 1 H and 13 C NMR spectra, including 1 J CH , of the azidomethanes are describes. The X-ray diffraction of derived triazole adducts 4 and 5 confirms the structure assignment and indicates in the case of 5 a 1,5-sigmatropic alkyl rearrangement

La reaction de phenyl-1 cyclohexene avec l'azoture de sodium donne un azido-1 iodo-2 phenyl-1 cyclohexane qui subit ensuite une solvolyse. Synthese d'azido-3 phenyl-1 cyclohexene a partir de phenyl-3 (ou 1) cyclohexene-1ol