(A) stereoselective synthesis of tetrahydropyran moiety in lanomycin and restricticin

Abstract

A highly stereoselective synthesis of the key intermediate 7 to the synthesis of restricticin and lanomycin was accomplished over 13 steps starting from the known diol 104. Starting diol 104 was readily obtained from D-tartaric acid over 3 steps in 74% overall yield. Alcohol 114 was oxidized by Swern conditions followed by coupling with (E)-crotylboronate 118 to give the desired alcohol 116 in 70% yield along with 10% of the isomeric alcohol 117. Alcohol 116 was subjected to etherification with methyl iodide, deprotection to triol, regioselective sulfonation of the primary hydroxyl group, epoxide formation and silylation with TBSCI in sequence to furnish epoxide 32 in 75% overall yield. Olefin 31 was ozonized and the resulting aldehyde was reduced to alcohol, which was converted into tetrahydropyran 6 in 81% overall yield in the presence of boron trifluoride etherate. The desired key intermediate 7 was obtained from 6 by the known procedure.