Imines reactions with crotyl organometallic compounds

BF3-OEt2 reverses the usual anti selectivity observed in tbe reaction of crotyl organometallic compounds (based on Cu, Cd, Hg, Sn, Tl, Ti, Zr, and V, but not on Mg, Zn, or B) with aldehydes (eq la) and imines (eq lb), so that homoallyl alcohols and homoallylamines are formed, respectively. " The products show mainly syn diastereoselectivity. BF3-OEt2 is the only Lewis acid which produces hydroxy- rather than halo-tetrahydropyrans from the reaction of aUyl-stannanes with pyranosides. The BF3-OEt2 mediated condensations of y-oxygenated allylstannanes with aldehydes (eq Ic) and with activated imines (eq Id) affords vicinal diol derivatives and 1,2-amino alcohols, respectively, with syn diastereoselectivity. The activated imines are obtained from... 

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