AN EFFICIENT STEREOSELECTIVE SYNTHESIS OF A RACEMIC CD-INTERMEDIATE OF VITAMIN-D

A highly efficient four-step approach to the racemic CD-intermediate 8 from the racemic hydrindenone 10 has been developed. In the key step, the hydrindenone 10 is converted stereoselectively into the (+/-)-bro mohydrindenone 17. Oxygen transposition from C-9 to C-8 is effected by means of conversion of 17 to the epoxide 20 and regioselective reduct ive ring opening of 20 with DIBALH. The resulting (+/-)-hydrindanol 8 was converted by the Horner-Wittig reaction with alpha-methacrolein in to the diene 24, hydrogenation of which provided the racemic hydrindan ol 25. This is a direct precursor of racemic Grundmann's ketone 9 and bears the alkyl side chain and the correct relative configuration at C 13, C14, C17, and C20 of Vitamin D.