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Regioselectivity in Intermolecular Pauson-Khand Reactions of Dissymmetric Fluorinated Alkynes

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journal contribution
posted on 17.12.2010, 00:00 by Jean-Claude Kizirian, Nuria Aiguabella, Albert Pesquer, Santos Fustero, Paula Bello, Xavier Verdaguer, Antoni Riera
Stoichiometric and catalytic intermolecular Pauson−Khand reactions (PKRs) of dissymmetric fluorinated alkynes were performed, affording regioselectively α-fluorinated cyclopentenones. Ethyl 4,4,4-trifluorobutynoate was an excellent substrate; its reaction with norbornadiene gave the corresponding PKR adduct in good yield and complete regioselectivity. Conjugate addition of nitroalkanes or cyanide to this adduct is stereospecific and entails concomitant loss of a trifluoromethyl group. This reaction can be exploited to prepare cyclopentenones featuring quaternary centers.