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
Reaction of meso-4-carbomethoxy-2-methylpentanal (1) with crotyltri-n-butyltin at −78°C in the presence of 1 eq BF3·OEt2, followed by the lactonization with BF3·OEt2, gave 6-(1-methylallyl)-3,4,5,6-tetrahydro-3,5-dimethyl-2-pyranone (2a) with the correct stereochemistry (erythro, anti-Cram) in 92% yield, which was converted to the title compound (3) in 85% yield upon the ozonolytic cleavage of the