Scope and limitation of organocuprates, and copper or nickel catalyst-modified Grignard reagents for installation of an alkyl group onto cis-4-cyclopentene-1,3-diol monoacetate

Coupling Reactions on Secondary Allylic, Propargylic, and Alkyl Carbons Using Organoborates/Ni and RMgX/Cu Reagents

In the first part of this review, secondary carbon-carbon bond formation by using allylic coupling reactions with aryl and alkenyl borates is presented. Early investigations have revealed the suitability of a nickel catalyst and [RTB(OMe)3]Li (RT: transferable group). Due to their low reactivity, the borates were converted to more reactive congeners possessing an alkanediol ligand, such as 2,3-butanediol and 2,2-dimethyl-1,3-propanediol. Borates with such diol ligands were used to install aryl and alkenyl groups on the monoacetate of 4-cyclopentenyl-1,3-diol. Furthermore, alkenyl borates showed sufficient reactivity toward less reactive allylic alcohol derivatives with bromine atoms at the cis position, producing dieneyl alcohols. In the second part, copper-based and/or copper-catalyzed substitutions of secondary allylic picolinates, propargylic phosphonates, and alkyl (2-pyridine)sulfonates with RMgX are briefly summarized. The application of these reactions to the synthesis of biologically active compounds is also discussed.

Synthetic molecular mimics of naturally occurring cyclopentenones exhibit antifungal activity towards pathogenic fungi

The naturally occurring reactive electrophilic species 12-oxo-phytodienoic acid (12-oxo-PDA) is a potent antifungal agent, whereas the plant growth regulator jasmonic acid, which is synthesized from 12-oxo-PDA, is ineffective. To address what structural features of the molecule endow it with antifungal activity, we synthesized a series of molecular mimics of 12-oxo-PDA varying in the length of the alkyl chain at its C-4 ring position. The octyl analogue (4-octyl cyclopentenone) was the most effective at suppressing spore germination and subsequent mycelial growth of a range of fungal pathogens and was particularly effective against Cladosporium herbarum and Botrytis cinerea, with minimum fungicidal concentrations in the range 100–200 µM. Introduction of a carboxyl group to the end of the chain, mimicking natural fatty acids, markedly reduced antifungal efficacy. Electrolyte leakage, indicative of membrane perturbation, was evident in both C. herbarum and B. cinerea exposed to 4-octyl cyclopentenone. Lipid composition analysis of the fungal spores revealed that those species with a high oil content, namely Fusarium oxysporum and Alternaria brassicicola, were less sensitive to 4-octyl cyclopentenone. The comparable hydrophobicity of 4-octyl cyclopentenone and 12-oxo-PDA accounts for the similar spore suppression activity of these two compounds. The relative ease of synthesis of 4-octyl cyclopentenone makes it an attractive compound for potential use as an antifungal agent.

Synthesis ofl-Carbafuranomycin, an Unnatural Analogue of the Antibiotic Amino Acid Furanomycin†,‡

[reaction: see text] L-(+)-carbafuranomycin is a novel analogue of L-(+)-furanomycin, an unusual antibiotic alpha-amino acid that attracted great interest due to its activity as an isoleucine antagonist. We present here a concise and efficient asymmetric synthesis of this carba-analogue starting with the 1,3-dipolar cycloaddition of a chiral nitrile oxide with cyclopentadiene. Notably, the methyl group was introduced by an S(N)2' cuprate substitution with high stereo- and regioselectivity.

Catalytic Regiodivergent Kinetic Resolution of Allylic Epoxides: A New Entry to Allylic and Homoallylic Alcohols with High Optical Purity

A novel regiodivergent kinetic resolution of a series of allylic epoxides with alkylzinc reagents is described. Results demonstrate the potential of chiral copper-phosphoramidite catalysts for enantiomer differentiation of allylic epoxides, allowing a chiral catalyst-stereoregulated synthesis of cyclic allylic and homoallylic alcohols with high optical purities.

Regio- and stereoselective ring openings of 3-Aza-2-oxabicyclo[2.2.1]hept-5-ene systems with copper catalyst-modified grignard reagents: application to the synthesis of an inhibitor of 5-lipoxygenase

Treatment of acylnitroso hetero Diels-Alder cycloadducts 2 with organomagnesium reagents in the presence of a catalytic amount of copper induces ring opening to afford predominantly monocyclic anti-1,2-hydroxamic acids 12. Alkylmagnesium reagents were found to give superior regio- and stereoselectivities compared with vinyl and arylmagnesium reagents. This cycloadduct ring opening methodology was applied to the synthesis of a unique cyclopentenyl hydroxamic acid-based inhibitor of 5-lipoxygenase.