Methods of Synthesis of Thia Analogues of Gonasteroids

Abstract

The voluminous literature that appeared on thiasteroids, especially after the publication of our earlier review on this subject,¹ prompted us to highlight exclusively the recent progress achieved in the total syntheses of a large variety of thia analogues of gonasteroids otherwise known as thiagonanes. These modified steroids have drawn the attention of steroid chemists for the following reasons: (i) their preparation itself constitutes a stimulating exercise to the organic chemist, often demanding development of new synthetic approaches of general utilitarian value; (ii) the investigations concerning the reaction mechanisms and stereochemistry, based on the steroidal framework, provide fundamentally significant and often fascinating chemical problems; (iii) as common with conformationally rigid molecules, the spectral properties, especially in ¹H and ¹³C NMR, of these heterogonasteroids may reveal quite interesting features. The introduction of a heteroatom like sulfur, oxygen or nitrogen in place of a methylene group at various positions in the steroid skeleton has recently been achieved by partial and total syntheses. The present review on the syntheses of thiagonanes is divided for convenience into eight sections (I VIII), mainly based on the position of the sulfur atom in the steroidal nucleus.