allylsilane 3a with excellent diastereoselectivity. Dihydropyrans 2a and 2b were prepared from optically pure acyclic acetals via ring-closing metathesis. Coupling of 3a and 2a or 2b via the carbon-Ferrier protocol gave trans-2,6-disubstituted dihydropyrans 30 and 35 with complete stereoselectivity. Vanadium-based pinacol coupling reactions were explored for closure of the medium-sized carbocycle to yield
sequence that involves a SmI2-promoted stereoselective Reformatsky addition of chiral nonracemic α-bromo α′-sulfinyl ketones to various aldehydes followed by stereoselective reduction of the Reformatsky adduct. The absolute configuration of the products was determined by comparison with literature data and by 1H NMR NOESY experiments. The observed stereoselectivities can be explained in terms of a boat