CHEMISTRY OF PHOSPHORYLMETHYL ISOCYANIDES .5. INTRODUCTION OF 20-KETOSIDE-CHAINS IN 17-OXOSTEROIDS - WITTIG-HORNER-EMMONS REACTIONS OF ONO)ISOCYANOMETHYLENE]-3-METHOXYANDROSTA-3,5-DIENE

The synthesis is described of a series of polyfunctional unsaturated D ELTA16,20-20-isocyanosteroids 5a-f by the Wittig-Horner-Emmons reactio n of (E)-17-[(diethylphosphono)isocyanomethylene] steroid 4 with sever al aldehydes and with acetone. Hydrolysis of the isocyanosteroids 5a-f with dilute sulfuric acid gave DELTA16-20-ketosteroids 6a-f in high y ield. Hydrolysis of 5a was also possible under neutral conditions, via the intermediate DELTA16-20-20-isocyanatosteroid 7a, leading to A-rin g protected 16-dehydroprogesterone 8a. The Wittig-Horner-Emmons reacti on, together with the described hydrolyses, provides a new method for the introduction of steroid side chains. The method is particularly su ited for side chains of different size, structure, and functionality.