| Abstract
| - PdCl2(CH3CN)2 (10 mol %) catalyzed reactions of non-3-ene-2,8-diols 1 and 2 gave 2,6-disubstitutedtetrahydropyrans 3 and 4 in excellent yields with high diastereoselectivities (>20:1). Intramolecularcyclizations of the hydroxy nucleophile to the chiral allylic alcohol take place efficiently under mildconditions. A new stereogenic center is generated on the tetrahydropyran ring by 1,3-chirality transferfrom the chiral allylic alcohol via a syn-SN2‘ type process. Cis tetrahydropyran 3E was formed fromsyn-2,8-diols 1a and 2a, and trans tetrahydropyran 4E was formed from anti-2,8-diol 1b, stereospecifically.Cis tetrahydropyran bearing a cis alkene 3Z was obtained from 2b at −40 °C, while 4E was formed from2b in the presence of catalytic amount of water at −40 °C. The face selectivity of these cyclizations canbe rationalized by taking a favorable conformation of the intermediary Pd π-complex with allylic alcohols,escaping the allylic strain and 1,3-diaxial interactions. A stereocontrolled synthesis of optically pure2-alkenyl-6-methyltetrahydropyran 17 was achieved efficently in four steps from 6-silyloxy-1-heptyne13 with an aldehyde and included asymmetric alkynylation, partial reduction of alkyne, deprotection ofthe silyl group, and the stereospecific cyclization.
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