Prepn from ethyl cholanate: Wieland et al., Z. Physiol. Chem. 161, 80 (1926); from 3,7-diketonorcholanic acid: Windaus, van Schoor, ibid. 173, 312 (1928); from 12-ketonorcholanic acid: Cook, Haslewood, J. Chem. Soc. 1934, 428; from 3α,23-dihydroxycholanic acid: Yanuka et al., Tetrahedron Lett. 1968, 1725.