Transformations of steroidal neopentyl systems. Part V. Synthesis and proof of the configuration of 19a-methyl-19S-alcohols
The synthesis of steroidal 19a-methyl-19S-alcohols by lithium aluminium hydride reduction of the 19a-methyl-19-ketones is described. In contrast to the 19R-alcohol, the 19S-alcohol could not be converted, under standard conditions, to the 3α-methoxy-3β, 19-oxide (5α-H). The results are consistent with the hypothesis that the rotation around the C(10)–C(19) bond in 19a-methyl-19ξ-alcohols is severely restricted.