erythro-3-alkyl-2-hydroxypropionate unit in (4) is predominantly obtained via the reaction of but-2-enylstannane (2a) with glyoxylateesters (3) while the threo-isomer (5) is preferentially produced via 9-but-2-enyl-9-borabicyclo[3.3.1] nonane (2b); the former reaction has been applied to the enantioselective synthesis of verrucarinolactone (6).
The reaction of crotyltrialkylstannanes (1) with aldehydes in the presence of BF3,OEt2, produces the corresponding erythro homoallyl alcohols (2) predominantly regardless of the geometry of the double bond. Further, the Lewis acid mediated reaction exhibits the enhanced Cram selectivity in comparison with other allylic organometallic reactions which proceed in the absence of Lewis acids. Use of AlCl3-i-PrOH