D-homo-steroids. Part III. The preparation of D-homoandrostane derivatives: a study of the reactions of steroidal C(17)-spiro-oxirans and their derivatives

Abstract

The readily availability of steroidal C(l7)-spirooxirans (VI), by the action of either dimethylsulphonium methylide or dimethyloxosulphonium methylide on 17-ketonesJg made the oxirans attractive as precursors of D-homoandrostane derivatives.l0 We envisaged either (a) the conversion of the oxiran into the amino-alcohol (HI), with subsequent use of nitrous acid as in the older route, or (b) the formation of a different 17,20-disubstituted compound (VII) suitable for a pinacolic or semipinacolic type of rearrangement. The requirement here was an effective ' leaving group ' (X) at C(20). We therefore studied the behaviour of the C(17)-spiro-oxirans with a variety of reagents providing nucleophilic species which might attack C(20).Pye$ayation of 3p-Hyd~oxy-~-homoandrost-5-en-l7a-one and -17-one.-The conversion of 3 p-hydroxyandrost-5-en-17-one into the C(17)-spiro-oxirans (VIa and b) followed essentially the published procedures>~~ though with minor modifications (see Experimental section). Incidentally we found that prolonged contact of the 3p-hydroxy-17-ketone with dimethylsulphonium methylide in the presence of an excess of trimethylsulphonium iodide gave the 3~-methoxy-compound in high yield. O-Methylation by this salt does not appear to have been reported previously, although trimethyloxosulphonium iodide is described as a methylating agent for phenols.11 This side reaction was avoided by limiting the reaction time to 1 h, after which the product no longer showed i.r. absorption at 1740 cm-l due to the 17-ketone.

Unimolecular micelles: Synthesis and characterization of amphiphilic polymer systems

“…Briefly, triethylene glycol monomethyl ether was mesylated, 25 treated with sodium azide, 26 and reduced by zinc/acetic acid 27 to give the monomethyl triethylene glycol amine.…”

Studies Toward the Total Synthesis of Pluraflavin A

“…No reaction was observed with many known reducing agents, such as propanedithiol, [32] dithiothreitol, [Et 3 NH][SnSPh 3 ], [33] SnCl 2 •2H 2 O, [34] HSnBu 3 , and H 2 SnBu 2 . [33] Reduction did occur with H 2 in the presence of Pd/C or Lindlar’s catalyst [35] and Zinc/acetic acid [36] but these conditions were incompatible with the pluraflavin core, resulting in decomposition.…”

Recent Applications and Developments of Organic Azides in Total Synthesis of Natural Products

“…Typical procedures of azide reduction to amine, and the conditions azides are tolerant.A notable example of selective azide reduction in natural product synthesis was reported byMolander et al in 1999 (Scheme 36) [84].In their total synthesis of cylindricin C 193, azide moiety in 190 had to be reduced to amine in the presence of carbonyl and conjugated olefins. After investigations, freshly prepared chromium (II) chloride solution[85][86][87] successfully reduced the azide chemoselectively to give primary amine 191 which gave double aza-Michael addition product spontaneously. The obtained 192 was deprotected to afford cylindricin C 193.…”