Alcohol inversion of 17β-steroids

Inversion of 17β-steroids has been accomplished using a modified Mitsunobu protocol in which 4-nitrobenzoic acid is employed as the acidic component. Excellent yields of inverted product were obtained for a number of representative steroid families including estrogens, equilenins, and androgens. Application of this methodology to the synthesis of 17α-dihydroequilenin is described.