title: Germanium(II)-mediated reductive cross-aldol reaction of bromoaldehydes with aldehydes: NMR studies and ab initio calculations.
abstract: A highly practical reductive cross-aldol reaction of alpha-bromoaldehydes with various aldehydes has been developed using Ge(II)Cl 2 to produce aldehyde germanium(IV) aldolates, which were directly transformed to various multifunctionalized compounds. A remarkable change in stereoselectivity depended on the alpha-bromoaldehydes employed; secondary alpha-bromoaldehydes gave syn selectivities, while tertiary alpha-bromoaldehydes accomplished the synthesis of anti-selective aldol products with a quaternary carbon center. NMR studies and X-ray analysis strongly suggested the formation of germanium enolate in the reaction of alpha-bromoaldehyde 2h with GeCl 2-dioxane. Detailed mechanistic studies, including NMR analysis and ab initio calculations, revealed the generation of stable germanium aldolates, which was due to the remarkably low Lewis acidity of the germanium(IV).
authors.affiliation: Department of Applied Chemistry and Center for Atomic and Molecular Technologies (CAMT), Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan.
authors.forename: Shin-ya
authors.initials: SY
authors.lastname: Tanaka
authors.forename: Nobuo
authors.initials: N
authors.lastname: Tagashira
authors.forename: Kouji
authors.initials: K
authors.lastname: Chiba
authors.forename: Makoto
authors.initials: M
authors.lastname: Yasuda
authors.forename: Akio
authors.initials: A
authors.lastname: Baba