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Hypothemycin, an epoxide derivative of (5

The dehydration of maleamic acids using methanesulfonyl chloride as a dehydrating agent to selectively and rapidly (

Simple conditions using AlCl3 for the regioselective intermolecular mono- or bis-hydroalkoxylation of allenamides are presented. The reactions showed good functional group tolerance and an initial mechanistic analysis is presented.

GPR55 is an orphan G-protein coupled receptor involved in various pathophysiological conditions. However, there are only a few noncannabinoid GPR55 ligands reported so far. The lack of potent and selective GPR55 ligands precludes a deep exploration of this receptor. The studies presented here focused on a thienopyrimidine scaffold based on the GPR55 antagonist ML192, previously discovered by high-throughput screening. The GPR55 activities of the new synthesized compounds were assessed using β-arrestin recruitment assays in Chinese hamster ovary cells overexpressing human GPR55. Some derivatives were identified as GPR55 antagonists with functional efficacy and selectivity versus CB1 and CB2 cannabinoid receptors., M.E.A., P.H.R., and N.J. are supported by National Institutes of Health grant R01 DA0455698. M.E.A. and P.Z. thank the financial support NIH P30 DA013429. P.M. and N.J. are supported by the Ministry of Science, Innovation, and Universities, Spain (MCIU)/FEDER grant RTI2018-095544-B-I00 and the Spanish National Research Council (CSIC) grant PIE-201580E033. P.M. acknowledges the Comunidad de Madrid (CM) programme “Atraccion de Talento” number 2018-T2/BMD-10819 and “Juan de la Cierva Incorporación Programme-MICIU” (IJC 2019-042182-I)

Resorcylic acid lactones (RALs) with a cis-enone moiety, represented by hypothemycin (1) and (5Z)-7-oxozeaenol (2), are fungal secondary metabolites with irreversible inhibitory activity against protein kinases, with particularly selective activity for inhibition of TAK1 (transforming growth factor beta-activated kinase 1). Gram-scale quantities of these compounds were needed as feedstock for semi-synthesizing RAL-analogues in a step-economical fashion. To do so, this study had three primary goals: identifying fungi that biosynthesized 1 and 2, enhancing their production by optimizing the fermentation conditions on the lab scale, and developing straight forward purification processes. After evaluating 536 fungal extracts via an in-house dereplication protocol, three strains were identified as producing cis-enone RALs (i.e., MSX78495, MSX63935, MSX45109). Screening these fungal strains on three grain-based media revealed enhanced production of 1 by strain MSX78495 on oatmeal medium, while rice medium increased the biosynthesis of 2 by strain MSX63935. Furthermore, the purification processes were improved, moving away from HPLC purification to utilizing two to four cycles of resuspension and centrifugation in small volumes of organic solvents, generating gram-scale quantities of these metabolites readily. In addition, studying the chemistry profiles of strains MSX78495 and MSX63935 resulted in the isolation of ten other RALs (3-12), two radicinin analogues (13-14), and six benzopyranones (15-20), with 19 and 20 being newly described chlorinated benzopyranones.

Regioselective intermolecular mono- or bis-hydroalkoxylation of allenamides with alcohols using simple aluminum-catalyzed reaction conditions is reported. When the reaction was carried out with 1.1 equivalents of alcohol at 50 °C, N,O-acetals were generated by 1,2-addition of an alcohol. An increase in temperature to 80 °C leads to γ-substituted ethers by an intermolecular isomerization process. Treatment with an excess of alcohol (3 equiv.) at 50 °C gave 1,3-bis(alkoxy)propanamines. The reactions exhibited good functional group tolerance and efficiency, affording the products in moderate to good yields.

Isocarbacyclin is a valuable synthetic analogue of prostacyclin with potential neuroprotective effects for the treatment of ischemic stroke. Herein, we describe the synthesis of isocarbacyclin and bicyclic analogues in only 7-10 steps, with the ω-side chain diversified at a late stage. A combination of new reaction design, function-oriented synthesis, and late-stage diversification led to a series of compounds that were tested for their neuroprotective activities. Efforts toward the synthesis of tricyclic analogues of isocarbacyclin, using the same combination of metal-catalyzed reactions, is also described.

A comprehensive mechanistic examination of an asymmetric palladium-catalyzed Tsuji–Trost allylation reaction that identifies the enantioselective step was completed utilizing DFT computational tools and the nudged elastic band method. Key components of the study include (a) plausible reaction pathways for the full interconversion of a square-planar palladium allyl enolate intermediate with low barriers relative to the subsequent enantioselectivity-determining reductive C–C coupling step, thereby disputing the previously identified mechanism, (b) a detailed analysis of the factors influencing the stereochemical control involved in forming the preferred configuration via the reductive C–C coupling step, (c) a comprehensive examination of the competing outer-sphere mechanism that includes a metal counterion as an escort to the nucleophile in order to modulate the effects of modeling the reaction step of oppositely charged species, and (d) examination of the possible role water plays in stabilizing a keto-coordinated adduct of PdII-?1-allyl, formed early in the catalytic cycle, relative to a carboxylate-coordinated adduct, the known resting state of the reaction. Barrier energies for the enantioselective C–C coupling are investigated with several levels of theory, and together they support a reaction mechanism consistent with the preferred formation of the correct enantiomer on the basis of the enantiomer of the ligand selected.

A palladium(II) catalyst, in the presence of Selectfluor, enables the efficient and chemoselective transformation of primary amides into nitriles. The amides can be attached to aromatic rings, heteroaromatic rings, or aliphatic side chains, and the reactions tolerate steric bulk and electronic modification. Dehydration of a peptaibol containing three glutamine groups afforded structure–activity relationships for each glutamine residue. Thus, this dehydration can act similarly to an alanine scan for glutamines via synthetic mutation.

[2017-2018 UNCG University Libraries Open Access Publishing Fund Grant Winner.] Griseofulvin is a fungal metabolite and antifungal drug used for the treatment of dermatophytosis in both humans and animals. Recently, griseofulvin and its analogues have attracted renewed attention due to reports of their potential anticancer effects. In this study griseofulvin (1) and related analogues (2–6, with 4 being new to literature) were isolated from Xylaria cubensis. Six fluorinated analogues (7–12) were synthesized, each in a single step using the isolated natural products and Selectflour, so as to examine the effects of fluorine incorporation on the bioactivities of this structural class. The isolated and synthesized compounds were screened for activity against a panel of cancer cell lines (MDA-MB-435, MDA-MB-231, OVCAR3, and Huh7.5.1) and for antifungal activity against Microsporum gypseum. A comparison of the chemical space occupied by the natural and fluorinated analogues was carried out by using principal component analysis, documenting that the isolated and fluorinated analogues occupy complementary regions of chemical space. However, the most active compounds, including two fluorinated derivatives, were centered around the chemical space that was occupied by the parent compound, griseofulvin, suggesting that modifications must preserve certain attributes of griseofulvin to conserve its activity.

Phenylcyanocarbene was generated by the reaction of azide with a hypervalent iodonium alkynyl triflate and reacted in situ with 21 different carbocyclic and heterocyclic aromatic compounds. These reactions led to more complex products that frequently underwent subsequent rearrangements. The reactivity was further explored in a mechanistic study to ascertain the chemoselectivity and stereospecificity.

Dienoic acids and pentadienyl alcohols are coupled in a decarboxylative and dehydrative manner at ambient temperature using Pd(0) catalysis to generate 1,3,6,8-tetraenes. Contrary to related decarboxylative coupling reactions, an anion-stabilizing group is not required adjacent to the carboxyl group. Of mechanistic importance, it appears that both the diene of the acid and the diene of the alcohol are required for this reaction. To further understand this reaction, substitutions at every unique position of both coupling partners was examined and two potential mechanisms are presented.

The first structure-activity relationships for a benzothiazole scaffold acting as an antagonist at GPR35 is presented. Analogues were designed based on a lead compound that was previously determined to have selective activity as a GPR35 antagonist. The synthetic route was modular in nature to independently explore the role of the middle and both ends of the scaffold. The activities of the analogues illustrate the importance of all three segments of the compound.

Conditions for the first palladium-catalyzed chemoselective protodecarboxylation of polyenoic acids to give the desired polyenes in good yields are presented. The reactions proceed under mild conditions using either a Pd(0) or Pd(II) catalyst and tolerate a variety of aryl and aliphatic substitutions. Unique aspects of the reaction include the requirement of phosphines, water, and a polyene adjacent to the carboxylic acid.

Spiroscytalin (1), a new tetramic acid that possesses an uncommon spiro-ring fusion between a polyketide-derived octalin ring system and a 2,4-pyrrolidinedione, along with two known compounds, leporin B (2) and purpactin A (3), were isolated from a solid phase culture of the fungus Scytalidium cuboideum (MSX 68345). The molecular connectivity of 1–3 was determined using NMR spectroscopy and mass spectrometry. The relative configurations of 1 and 2 were determined by NOESY experiments. The absolute configuration of 1 was determined by electronic circular dichroism (ECD) via a combination of experimental measurements and computational calculations. While leporin B was known, it displayed activities that had not been reported previously, including cytotoxicity against three human tumor cell lines and antibacterial activity against Candida albicans and Staphylococcus aureus.

(5Z)-7-Oxozeanol and related analogues were isolated and screened to explore their activity as TAK1 inhibitors. Seven analogues were synthesized and more than a score of natural products isolated that examined the role that different areas of the molecule contribute to TAK1 inhibition. A novel nonaromatic difluoro-derivative was synthesized that had similar potency compared to the lead. This is the first example of a nonaromatic compound in this class to have TAK1 inhibition. Covalent docking for the isolated and synthesized analogues was carried out and found a strong correlation between the observed activities and the calculated binding.

GPR55, a G protein-coupled receptor, is an attractive target to alleviate inflammatory and neuropathic pain and treat osteoporosis and cancer. Identifying a potent and selective ligand will aid to further establish the specific physiological roles and pharmacology of the receptor. Towards this goal, a targeted library of 22 compounds was synthesized in a modular fashion to obtain structure-activity relationship information. The general route consisted of coupling a variety of p-aminophenyl sulfonamides to isothiocyanates to form acylthioureas. For the synthesis of a known naphthyl ethyl alcohol motif, route modification led to a shorter and more efficient process. The 22 analogues were analyzed for their ability to serve as agonists at GPR55 and valuable information for both ends of the molecule was ascertained.

Unique reactivity of a rhodium catalyst in the presence of many different Lewis basic additives was observed and studied. In the absence of additives, it was observed that a selective [2+2+2] reaction to form benzene products occurred; however, in the presence of an additive, optimally DMSO, the first rhodium(I)-catalyzed [2+2+2+2] reaction of alkynes occurred. A screen of different additives and catalysts was performed. Finally, a brief mechanistic study per-formed by using a ReactIR determined that DMSO coordinates to the catalyst, which affects the energetics of the reaction pathway. This appears primarily to raise the transition-state energy for the reductive elimination to form the benzene products.

GPR55 is a class A G protein-coupled receptor (GPCR) that has been implicated in inflammatory pain, neuropathic pain, metabolic disorder, bone development, and cancer. Initially deorphanized as a cannabinoid receptor, GPR55 has been shown to be activated by non-cannabinoid ligands such as l-α-lysophosphatidylinositol (LPI). While there is a growing body of evidence of physiological and pathophysiological roles for GPR55, the paucity of specific antagonists has limited its study. In collaboration with the Molecular Libraries Probe Production Centers Network initiative, we identified a series of GPR55 antagonists using a β-arrestin, high-throughput, high-content screen of ~300000 compounds. This screen yielded novel, GPR55 antagonist chemotypes with IC50 values in the range of 0.16-2.72 μM [Heynen-Genel, S., et al. (2010) Screening for Selective Ligands for GPR55: Antagonists (ML191, ML192, ML193) (Bookshelf ID NBK66153; PMID entry 22091481)]. Importantly, many of the GPR55 antagonists were completely selective, with no agonism or antagonism against GPR35, CB1, or CB2 up to 20 μM. Using a model of the GPR55 inactive state, we studied the binding of an antagonist series that emerged from this screen. These studies suggest that GPR55 antagonists possess a head region that occupies a horizontal binding pocket extending into the extracellular loop region, a central ligand portion that fits vertically in the receptor binding pocket and terminates with a pendant aromatic or heterocyclic ring that juts out. Both the region that extends extracellularly and the pendant ring are features associated with antagonism. Taken together, our results provide a set of design rules for the development of second-generation GPR55 selective antagonists.

The reactivity of a series of 1,5-disubstituted sulfonyl-triazoles was explored using either thermolytic or metal-catalyzed conditions. Both the thermolysis and the Rh(II)-catalyzed reactions led to the synthesis of a-sulfonyl-nitriles, which presumably occurred through a carbene or carbenoid mechanism. The reactivity of the carbenes and carbenoids resulting from the loss of dinitrogen from the 1,5-disubstituted sulfonyl-triazoles were different from those of the previously explored 1,4-disubstituted sulfonyl-triazoles. It was observed by NMR that the Rh(II)-catalyst coordinates strongly but reversibly with the 1,5-disubstituted sulfonyl-triazoles. Other catalysts, including both Bronsted and Lewis acids, were found to catalyze this transformation, although less efficiently compared to neat thermolysis or Rh(II)-catalyzed conditions. These data illustrate both the unique nature of 1,5-disubstituted sulfonyl-triazoles and potential future avenues for their utilization.

The mechanism for the biomimetic synthesis of flavonolignan diastereoisomers in milk thistle is proposed to proceed by single-electron oxidation of coniferyl alcohol, subsequent reaction with one of the oxygen atoms of taxifolin's catechol moiety, and finally, further oxidation to form four of the major components of silymarin: silybin A, silybin B, isosilybin A, and isosilybin B. This mechanism is significantly different from a previously proposed process that involves the coupling of two independently formed radicals.

Silymarin, an extract of the seeds of milk thistle (Silybum marianum), is used as an herbal remedy, particularly for hepatoprotection. The main chemical constituents in silymarin are seven flavonolignans. Recent studies explored the non-selective methylation of one flavonolignan, silybin B, and then tested those analogues for cytotoxicity and inhibition of both cytochrome P450 (CYP) 2C9 activity in human liver microsomes and hepatitis C virus infection in a human hepatoma (Huh7.5.1) cell line. In general, enhanced bioactivity was observed with the analogues. To further probe the biological consequences of methylation of the seven major flavonolignans, a series of 7-O-methylflavonolignans were generated. Optimization of the reaction conditions permitted selective methylation at the phenol in the 7-position in the presence of each metabolite’s 4–5 other phenolic and/or alcoholic positions without the use of protecting groups. These 7-O-methylated analogues, in parallel with the corresponding parent compounds, were evaluated for cytotoxicity against Huh7.5.1 cells; in all cases the monomethylated analogues were more cytotoxic than the parent compounds. Moreover, parent compounds that were relatively non-toxic and inactive or weak inhibitors of hepatitis C virus infection had enhanced cytotoxicity and anti-HCV activity upon 7-O-methylation. Also, the compounds were tested for inhibition of major drug metabolizing enzymes (CYP2C9, CYP3A4/5, UDP-glucuronsyltransferases) in pooled human liver or intestinal microsomes. Methylation of flavonolignans differentially modified inhibitory potency, with compounds demonstrating both increased and decreased potency depending upon the compound tested and the enzyme system investigated. In total, these data indicated that monomethylation modulates the cytotoxic, antiviral, and drug interaction potential of silymarin flavonolignans.

Compound (I) is shown to exhibit moderate antitumoric activity and no antimicrobial activity.

We recently reported two unexplored reactivities of alkynes and azides. The first method reacts nucleophilic alkynes and electrophilic azides to synthesize sulfonyl-substituted 1,5-disubstituted 1,2,3-triazoles. The second method reacts electrophilic alkynes with nucleophilic azides to form alkynyl azides that immediately extrude dinitrogen to form cyanocarbenes which were trapped by O–H insertion, sulfoxide complexation, and cyclopropanation. The design and discovery of these reactions, along with key observations, is discussed herein.

The reaction of acetylides with sulfonyl azides was found to selectively form 1,5-substituted sulfonyl triazoles. This reaction thus provides access to the regioisomeric product as compared to the popular copper-catalyzed azide-alkyne cycloaddition. The reaction is efficient and selective with a variety of alkyne sources and sulfonyl azides and can incorporate an additional electrophile to yield 1,4,5-trisubstituted sulfonyl triazoles.

A synthetic route to a mycosamine donor was designed and provided access to a set of AmB derivatives targeted to probe the effect of the C2'-OH. It was determined that the configuration of the C2'-position is inconsequential but that O-methylation of this alcohol was deleterious to its mode of action. Additionally, the analog incorporating a mycosamine derivative from the enantiomeric series was devoid of activity.

Metal-catalyzed diene-yne, diene-ene, and diene-allene [2+2+1] cycloaddition reactions provide new methods for the facile construction of highly functionalized five-membered rings. These reactions can be conducted with a variety of substrate substitution patterns and functional groups and often in the absence of solvent. The special reactivity of dienes, a key to enabling or enhancing the effectiveness of the [2+2+1] and other reactions, is significantly different from that of alkynes, alkenes, or allenes. For example, the [2+2+1] reaction of a diene-yne is accelerated compared to that of the corresponding ene-yne. An even more dramatic "diene effect" is found with diene-enes and diene-allenes. While bis-enes and ene-allenes are not reported to yield [2+2+1] cycloadducts, the related diene-enes and diene-allenes undergo efficient [2+2+1] cycloadditions, providing new routes to cyclopentanones and alkylidenecyclopentanones. Mechanistic studies suggest that the unique reactivity observed with dienes arises from their participation in the putative rate-determining reductive elimination step by providing an additional energy-lowering coordination site for the transition metal catalyst.

A novel metal-catalyzed, all-alkene [2+2+2] cycloaddition reaction involving a strained and conformationally restricted bis-ene and a diene is reported. Modification of the catalyst leads to competition with a diene-ene [2+2] reaction, and when an alkyne was used in place of the diene, [2+2+2] and [2+2+2+2] cycloaddition reactions occurred involving the bis-ene and 1 or 2 equiv of the alkyne.

We present our step-economical synthesis of clinprost, the methyl ester of isocarbacyclin, and analogs. Isocarbacyclin is a valuable target due to its neuroprotection from the oxidative damage after a stroke. Specifically, we utilized a palladium-catalyzed decarboxylative coupling of a pentadienyl dienoate, a rhodium-catalyzed diene-diene [2+2+1] cycloaddition, and a ruthenium-catalyzed cross-metathesis reaction. The decarboxylation reaction is the first decarboxylation of its type since the carboxyl-bearing carbon does not possess an anion-stabilizing group. In this chapter, we present some of our research into this novel reaction. The diene-diene [2+2+1] cycloaddition is the first cyclocarbonylation between two dienes. The metathesis reaction is particularly valuable since it allows for late-stage diversification. These three metal-catalyzed reactions enabled us to complete the synthesis of clinprost in nine steps, seven for some analogs, instead of the 15 or more steps that have been previously reported.

A series of 1,3,4-oxadiazol-2-ones was synthesized and tested for activity as antagonists at GPR55 in cellular beta-arrestin redistribution assays. The synthesis was designed to be modular in nature so that a sufficient number of analogues could be rapidly accessed to explore initial structure-activity relationships. The design of analogues was guided by the docking of potential compounds into a model of the inactive form of GPR55. The results of the assays were used to learn more about the binding pocket of GPR55. With this oxadiazolone scaffold, it was determined that modification of the aryl group adjacent to the oxadiazolone ring was often detrimental and that the distal cyclopropane was beneficial for activity. These results will guide further exploration of this receptor.

Studies on the viability of the type II nickel-catalyzed intramolecular [4+4] cycloaddition of bis-dienes show that it is influenced by both diene substitution and geometry. Both E- and Z-isomers of 19 and 20 react, albeit at markedly different rates, to afford cycloadducts, whereas only the Z-isomer of 9 (and not the E-isomer) reacts to give 8 and 25. Chemoselective elaboration of 8 to (±)-salsolene oxide (7) was used to confirm the cycloadduct structure while establishing a step economical route to the natural product.

The procedures described in this article involve the synthesis and isolation of hypervalent iodonium alkynyl triflates (HIATs) and their subsequent reactions with azides to form cyanocarbene intermediates. The synthesis of hypervalent iodonium alkynyl triflates can be facile, but difficulties stem from their isolation and reactivity. In particular, the necessity to use filtration under inert atmosphere at -45 °C for some HIATs requires special care and equipment. Once isolated, the compounds can be stored and used in reactions with azides to form cyanocarbene intermediates. The evidence for cyanocarbene generation is shown by visible extrusion of dinitrogen as well as the characterization of products that occur from O-H insertion, sulfoxide complexation, and cyclopropanation. A side reaction of the cyanocarbene formation is the generation of a vinylidene-carbene and the conditions to control this process are discussed. There is also potential to form a hypervalent iodonium alkenyl triflate and the means of isolation and control of its generation are provided. The O-H insertion reaction involves using a HIAT, sodium azide or tetrabutylammonium azide, and methanol as solvent/substrate. The sulfoxide complexation reaction uses a HIAT, sodium azide or tetrabutylammonium azide, and dimethyl sulfoxide as solvent. The cyclopropanations can be performed with or without the use of solvent. The azide source must be tetrabutylammonium azide and the substrate shown is styrene.

We recently reported two unexplored reactivities of alkynes and azides. The first method reacts nucleophilic alkynes and electrophilic azides to synthesize sulfonyl-substituted 1,5-disubstituted 1,2,3-triazoles. The second method reacts electrophilic alkynes with nucleophilic azides to form alkynyl azides that immediately extrude dinitrogen to form cyanocarbenes which were trapped by O–H insertion, sulfoxide complexation, and cyclopropanation. The design and discovery of these reactions, along with key observations, is discussed herein.

A step-economical synthesis of clinprost is reported that concludes with 3 different transition metal-catalyzed reactions: Pd-catalyzed decarboxylation with allylic rearrangement, Rh-catalyzed diene-ene [2+2+1] reaction, and Ru-catalyzed cross-metathesis reaction. The complexity bestowed to the molecule from these reactions converts a readily accessible ester to clinprost without using protecting groups in only 9 total steps.

When being purified by silica gel chromatography, isomerization of the products to 1,4-triazoles partially occurs.

Metal-catalyzed diene-yne, diene-ene, and diene-allene [2+2+1] cycloaddition reactions provide new methods for the facile construction of highly functionalized five-membered rings. These reactions can be conducted with a variety of substrate substitution patterns and functional groups and often in the absence of solvent. The special reactivity of dienes, a key to enabling or enhancing the effectiveness of the [2+2+1] and other reactions, is significantly different from that of alkynes, alkenes, or allenes. For example, the [2+2+1] reaction of a diene-yne is accelerated compared to that of the corresponding ene-yne. An even more dramatic "diene effect" is found with diene-enes and diene-allenes. While bis-enes and ene-allenes are not reported to yield [2+2+1] cycloadducts, the related diene-enes and diene-allenes undergo efficient [2+2+1] cycloadditions, providing new routes to cyclopentanones and alkylidenecyclopentanones. Mechanistic studies suggest that the unique reactivity observed with dienes arises from their participation in the putative rate-determining reductive elimination step by providing an additional energy-lowering coordination site for the transition metal catalyst.

Metal-catalyzed and metal-mediated [m + n +…(+ x)] higher-order cycloaddition reactions comprise a broad and versatile class of reactions that give access to rings of seven or more members. In this review, 17 different reaction classes, including two-, three-, and four-component processes, that provide methods for the synthesis of seven-, eight-, nine-, and ten-membered rings are surveyed covering the literature from 1993 to mid-2005.

(trans/cis) [13938-94-8] C37H30ClOP2Rh (MW 690.96) InChI = 1S/2C18H15P.CO.ClH.Rh/c2*1-4-10-16(11-5-1)19(17-12-6-2-7-13-17)18-14-8-3-9-15-18;1-2;;/h2*1-15H;;1H;/q;;;;+1/p-1 InChIKey = SGULOPRLUCGLSH-UHFFFAOYSA-M (trans) [15318-33-9] InChI = 1S/2C18H15P.CO.ClH.Rh/c2*1-4-10-16(11-5-1)19(17-12-6-2-7-13-17)18-14-8-3-9-15-18;1-2;;/h2*1-15H;;1H;/q;;;;+1/p-1 InChIKey = SGULOPRLUCGLSH-UHFFFAOYSA-M (cis) [16353-77-8] InChI = 1S/2C18H15P.CO.ClH.Rh/c2*1-4-10-16(11-5-1)19(17-12-6-2-7-13-17)18-14-8-3-9-15-18;1-2;;/h2*1-15H;;1H;/q;;;;+1/p-1 InChIKey = SGULOPRLUCGLSH-UHFFFAOYSA-M (catalyst for carbonylation,2 decarbonylation,3 carbonyl exchange,4 reduction,5 hydrometalation,6 and CH activation reactions;7 reagent for alkylation of acid chlorides8) Physical Data: mp 209–210 °C (trans isomer), 204–205 °C (cis isomer), 195–197 °C (trans/cis mixture); IR carbonyl stretching 1970 cm−1 (nujol mull), 1977 cm−1 (CHCl3). Solubility: sol chloroform and dichloromethane; moderately sol aromatic hydrocarbons and CCl4; insol ether, alcohols, and aliphatic hydrocarbons. Form Supplied in: bright yellow crystalline solid, widely available. Preparative Method: to a solution of RhCl3ċ3H2O (2 g, 7.6 mmol) in 70 mL of absolute ethanol is slowly added triphenylphosphine (7.2 g, 2.75 mmol) in 300 mL of boiling absolute ethanol. The solution becomes clear within 5 min, at which point sufficient (10–20 mL) 37% formaldehyde solution is added, causing the red solution to become pale yellow. After several minutes, yellow microcrystals precipitate. Upon cooling, the resulting crystals are washed with ethanol and diethyl ether, dried (4.5 g, 85%) and recrystallized from hot toluene.1c Handling, Storage, and Precautions: the complex is air-stable as a crystalline solid and can be stored without special precautions. In solution it readily reacts with oxygen, which therefore must be excluded during preparation and use of this reagent.

Step economy is a preeminent goal of synthesis. [1] It influences the length, efficiency, cost, time, separation, and environmental impact of a synthesis. Step economy is favored by the use of single, serial, or multicomponent reactions that proceed in one operation with a great increase in target revelant complexity. The design or discovery of such reactions is thus critical to extending the practical reach of organic synthesis. Toward this end, we have directed effort at the identification of new metal-catalyzed reactions, especially those which are forbidden or difficult to achieve in the absence of a catalyst. This program has thus far produced several new two-, three-, and four-component reactions, including [4+4], [2] [4+2], [3] [5+2], [4] [6+2], [5] [5+2+1], [6] [2+2+1], [7] [4+2+1], [7a] and [5+1+2+1] [8] cycloadditions. Herein, we report the first examples of the [2+2+1] cycloaddition reaction of diene– allenes and CO and preliminary examples of acceleration of this process by Bronsted acids.

Step economy is a preeminent goal of synthesis. [1] It influences the length, efficiency, cost, time, separation, and environmental impact of a synthesis. Step economy is favored by the use of single, serial, or multicomponent reactions that proceed in one operation with a great increase in target revelant complexity. The design or discovery of such reactions is thus critical to extending the practical reach of organic synthesis. Toward this end, we have directed effort at the identification of new metal-catalyzed reactions, especially those which are forbidden or difficult to achieve in the absence of a catalyst. This program has thus far produced several new two-, three-, and four-component reactions, including [4+4], [2] [4+2], [3] [5+2], [4] [6+2], [5] [5+2+1], [6] [2+2+1], [7] [4+2+1], [7a] and [5+1+2+1] [8] cycloadditions. Herein, we report the first examples of the [2+2+1] cycloaddition reaction of diene– allenes and CO and preliminary examples of acceleration of this process by Bronsted acids.

Initial examples of a Rh(I)-catalyzed [2+2+1] reaction of diene-enes and CO are described. This method allows for the facile, efficient, and diastereoselective construction of a variety of alkenyl cyclopentanones in good to excellent yields. Control studies show that the diene moiety is required for this process as bis-enes do not give the [2+2+1] products under the same conditions.