Synthesis of Methylene‐ and Alkylidenecyclopropane Derivatives

AbstractSince the methylenecyclopropane moiety is found in many biologically active natural substances, the synthesis of methylene‐ and alkylidenecyclopropanes remains a considerable challenge. In addition, an attractive feature is their surprising stability, accompanied by a high level of strain, conferring on them an otherwise unattainable chemical reactivity. The growing interest in the chemistry of these compounds has in its turn stimulated the development of alternative approaches to their skeleton, aimed at selectively introducing structural and chemical diversification. The three principal methods to synthesize these important compounds are based on the formation of the cyclopropane ring, the use of preformed cyclopropanes, and the use of preformed methylene‐ and alkylidenecyclopropanes. Abbreviations: Ac: acetyl; Ar: aryl; Bn: benzyl; Boc: tert‐butoxycarbonyl; Box: bisoxazoline; BTMSA: bis(trimethylsilyl)amide; Bu: butyl; Bz: benzoyl; C: cyclo; Cod: cyclooctadiene; Cp: cyclopentadienyl; Cy: cyclohexyl; Dba: (E,E)‐dibenzylideneacetone; DBU: 1,8‐diazabicyclo[5.4.0]undec‐7‐ene; DCE: 1,2‐dichloroethane; de: diastereomeric excess; DEAD: diethyl azodicarboxylate; DMAc: N,N‐dimethylacetamide; DME: 1,2‐dimethoxyethane; DMF: dimethylformamide; DOSP: N‐p‐dodecylbenzenesulfonylprolinate; Dppb: 1,4‐bis(diphenyl)phosphinoborane; Dppe: bis(diphenylphosphino) ethene; E: electrophile; ee: enantiomeric excess; Et: ethyl; Hex: hexyl; L: ligand; LDA: lithium diisopropylamide; LG: leaving group; MCPBA: 3‐chloroperoxybenzoic acid; Me: methyl; MEM: methoxyethoxymethyl; MOM: methoxymethyl; Mp: morpholinyl; Ms: mesyl; Naph: naphthyl; NFSI: N‐fluorobenzenesulfonimide; Ns: nosyl; Nu: nucleophile; Pent: pentyl; Ph: phenyl; PMB: p‐methoxybenzoyl; Pr: propyl; Py: pyridyl; SEM: 2‐(trimethylsilyl)ethoxymethyl; TASF: tris(dimethylamino)sulfonium difluorotrimethyl silicate; TBAF: tetra‐n‐butylammonium fluoride; TBS: tert‐butyldimethylsilyl; TEA: triethylamine; Tedicyp: cis,cis,cis‐1,2,3,4‐tetrakis(diphenylphosphinomethyl)cyclopentane; Tf: trifluoromethanesulfonyl; TFP: tris(2‐furyl)phosphine; THF: tetrahydrofuran; THP: tetrahydropyran; TMS: trimethylsilyl; Tol: tolyl; Ts: 4‐toluenesulfonyl (tosyl).