Direct synthesis of substituted tetrahydrofurans via regioselective dehydrative polyol cyclization cascades

A one-pot procedure for the conversion of 1,2,4,5-tetraols into substituted tetrahydrofuran moieties has been developed. This involves the regioselective sulfonylation of the terminal hydroxyl of the polyol array followed by sequential oxirane and oxolane formation under basic conditions. A survey of reaction conditions has defined the use of N-(2,4,6-triisopropylbenzenesulfonyl)imidazole as sulfonylation reagent, potassium tert-butoxide as base, and tert-butanol as solvent to be optimal. Under these conditions, 8-O-benzyl-octan-1,2,4,5,8-pentaol was converted stereospecifically into tetrahydrofurans in 62% yield. Polyol substrates were derived from Sharpless asymmetric dihydroxylation of 1,4-dienes. Hence, substituted tetrahydrofurans could be obtained stereospecifically from diene substrates in two operations.