Catalytic enantioselective dehydrogenative Si-O coupling of oxime ether-functionalized alcohols

Asymmetric silylation of alcohols is an unusual but effective approach to their kinetic resolution, and the Cu-H-catalyzed dehydrogenative Si-O coupling is particularly noteworthy as dihydrogen is formed as the sole by-product. Our laboratory had previously reported on diastereoselective (with silicon-stereogenic silanes) and enantioselective (with achiral silanes) Si-O couplings of azine donor-functionalized alcohols. The limitation, that is, the requirement of a nitrogen donor atom, prompted us to seek equally useful donor groups. Oxime ethers were identified as a suitable alternative, and we describe herein the preparation of a series of oxime ether-functionalized alcohols. To assess different substitution patterns in their kinetic resolution, these were tested in the reagent-controlled Si-O coupling using a silicon-stereogenic silane. The optimal substituents at the oxime carbon atom (dr=85:15 in the diastereoselective coupling) were then chosen for the related catalyst-controlled Si-O coupling but selectivity factors were only moderate. (C) 2011 Elsevier Ltd. All rights reserved.