Diels–Alder adducts of 2-acetoxyfuran as a route to 2,3-functionalized 4-hydroxycyclohexanones. Application of X-ray diffraction to the problem of regio- and stereochemistry

Abstract

The Diels–Alder adducts of 2-acetoxyfuran and maleic anhydride and 2-acetoxyfuran and chloromethylmaleic anhydride have been obtained and their dihydro derivatives manipulated in high yield to various 2,3-functionalized 4-hydroxycyclohexanones. In all cases the hemiketal acetate bridge of the oxabicyclo[2.2.1] derivatives was cleaved smoothly using sodium methoxide in methanol at 0 °C; however, in the case of the chloromethyl compounds the reaction proceeds further to give an almost quantitative yield of the corresponding fused cyclopropane derivatives. These sequences, starting from the readily accessible but seldom used 2-acetoxyfuran, are therefore extremely advantageous to gain rapid and efficient access to a number of 2,3-functionalized 4-hydroxycyclohexanones. In the case of the adduct involving chloromethylmaleic anhydride, stereochemistry and regiochemistry were established by X-ray diffraction on the dihydro derivative.