title: Preparation of Functionalized Dialkylzincs via a Boron-Zinc Exchange. Reactivity and Catalytic Asymmetric Addition to Aldehydes.
abstract: The hydroboration of olefins with Et(2)BH provides diethyl(alkyl)boranes 2 which readily undergo a boron-zinc exchange with Et(2)Zn providing a range of polyfunctional primary, secondary, and benzylic diorganozincs. The resulting diorganozincs 3 have been reacted with various electrophiles (allylic halides, acid chlorides, alkylidenemalonates, ethyl propiolate, nitroolefins) in the presence of CuCN.2LiCl with excellent yields. With secondary dialkylzincs prepared from diastereomerically pure diethyl(alkyl)boranes, the boron-zinc exchange occurs with loss of stereochemistry. The asymmetric addition of 3 to aldehydes in the presence of the chiral catalyst 55 furnishes optically active polyfunctional secondary alcohols (50 to over 96% ee).
authors.affiliation: Fachbereich Chemie der Philipps-Universität Marburg, D-35032 Marburg, Germany.
authors.forename: Falk
authors.initials: F
authors.lastname: Langer
authors.forename: Lothar
authors.initials: L
authors.lastname: Schwink
authors.forename: Arokiasamy
authors.initials: A
authors.lastname: Devasagayaraj
authors.forename: Pierre-Yves
authors.initials: PY
authors.lastname: Chavant
authors.forename: Paul
authors.initials: P
authors.lastname: Knochel