The carbonyldicobalt-mediated alkyne/allene/CO cocyclization gives 4-alkylidenecyclopentenones as the major [2+2+1] cycloadducts. The regio- and stereoselectivities depend mainly on the substitution pattern of both the alkyne and the allenic moieties, which can be rationalized using the Magnus mechanism. However, contrary to this model, and in agreement with more recent mechanistic studies, our results
Double Thiol-Chiral Brønsted Base Catalysis: Asymmetric Cross Rauhut–Currier Reaction and Sequential [4 + 2] Annulation for Assembly of Different Activated Olefins
the intermolecular cross Rauhut-Currierreaction of 2-cyclopentenone and isatin-based alkylidene malononitriles. The resulting chiral adducts were sequentially assembled with diverse electron-deficient olefins to furnish highly enantioenriched cyclohexane derivatives (up to 96:4 er, >19:1 dr). A similar catalytic system of 2-mercaptobenzoic acid and quinine was further developed for the reaction of
A general method for the preparation of 5-alkylidene-2-cyclopentenones and their 2-phenylsulfanyl substituted derivatives, involving the intramolecular acylation of cc-sulfinyl carbanions with cyclopentadiene-alpha,beta-unsaturated esters as the key reaction followed by flash vacuum pyrolysis, is described. The reactions start from readily available Diels-Alder adducts, synthons of alpha-carbanions of alpha,beta-unsaturated esters. (c) 2006 Elsevier Ltd. All rights reserved.