Studies on the construction of abutasterone-type and 24-epi-abutasterone-type side chains employing asymmetric dihydroxylation of (E)-20(22),24-cholestadiene

The synthesis of abutasterone-type side chain, (20R,22R,24S)-20,22,24,25-tetrahydroxy-6β-methoxy-3α,5-cyclo-5α-cholestane 4, and 24-epi-abutasterone-type side chain, (20R,22R,24R)-20,22,24,25-tetrahydroxy-6β-methoxy-3α,5-cyclo-5α-cholestane 6, by means of Sharpless asymmetric dihydroxylation of (E)-20(22),24-cholestadiene 1 is described. Construction of abutasterone-type side chain 4 was carried out by selective mono-dihydroxylation of diene 1 with (DHQ)2AQN, followed by dihydroxylation of the corresponding (24S)-hydroxy-20(22)-cholestene 2 with (DHQD)2AQN. In contrast, bis-dihydroxylation of 1 with either (DHQD)2PHAL or (DHQD)2AQN preferentially occurs to produce 24-epi-abutasterone-type side chain 6.