BD fragments

In correspondence with the three methods of building up the steroid skeleton considered in this chapter, the exposition of the material is divided into three sections. The first of them comprises total syntheses from BC fragments with the initial formation of ring A and the second syntheses with the initial formation of ring D. The third section comprises syntheses of steroid compounds from BD fragments. 

At the same time, the syntheses from BD fragments described in the third section are mainly used for the production of model compounds and tricyclic intermediates. The only exception is the synthesis of etianic acids described in Scheme 83. 

The synthesis of compounds (185) and (186) has also been performed from BD fragments (Schemes 80 and 82). 

The method of synthesizing steroid compounds from tricyclic analogs in which rings B and D in the initial BD fragment are linked by a two-carbon bridge containing the Cjg and C13 atom has found fairly wide application (Schemes 81-83). 

A brief communication has recently been published [417] on the total synthesis of steroid compounds from BD fragments in which ring D is formed from acyclic precursors and is not introduced in the finished state, as in the preceding syntheses of this section (Scheme 83). The general route of the synthesis is close to that for the preparation of equilenin analogs described in Chapter II (Scheme 31). 

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