Stereoselectivity of electrophile-promoted oxacyclizations of 1,4-dihydroxy-5-alkenes to 3-hydroxytetrahydropyrans

Stereoinduction from the allylic hydroxyl group of 1,4-dihydroxy-5-alkenes has been systematically explored with various alkene substitution patterns and electrophilic reagents. For formation of erythro-diastereomers of 2-substituted 3-hydroxytetrahydropyrans, mercuric trifluoroacetate-promoted cyclizations of cis- and (Z)-alkenyldiols generally give the highest diastereoselectivities. For the corresponding 1,4-dihydroxy-5-alkyne, mercuric triflate-catalyzed cyclization followed by triethylsilane reduction affords an alternative route to the erythro-diastereomer.