Synthesis of Some Five- and Six-Membered Oxasteroids of Cholestane Series by Ring Contraction and the Mass Spectrometric Fragmentations of Oxasteroids

Synthesis of several new five- and six-membered oxasteroids of the cholestane series by the ring contraction of those oxasteroids whose oxygen-containing ring is larger by one member has been achieved. Ring contraction utilizes a series of reactions recently developed by us for the transformation of cyclic ketones into cyclic ethers; it involves a regioselective β-scission of the alkoxyl radical generated by irradiation of the lactol hypoiodite derived from the starting oxasteroid to give the iodoformate followed by its cyclization. The present work demonstrates the versatility of our new method for the synthesis of cyclic ethers and extends the scope of its application. The mass spectral fragmentation of some oxasteroids synthesized in the present and previous work is discussed.