Synthetic applications of conjugated nitrones, 5. A novel entry to the 13-azasteroid system

Article abstract of DOI:10.1002/jlac.199619961120

A synthetic approach to 13-azasteroid and C-nor-13-azasteroid derivatives (type 17/18) as well as to the 4,13-diaza analogues 27/28 is described. For the construction of the tetracyclic compounds precursors with preformed rings A, B and D containing a conjugated nitrone system were used (16/26). These were prepared from the annulated cyclohexenones 10/ 20a, b in six steps according to slightly modified standard procedures. The failure in obtaining the terminal silyl alkynes 15b by Michael addition of the enolate of 14b to nitrostyrene is explained on the basis of a strong Si-O complexation. After replacement of the trimethylsilyl substituent by the sterically more demanding triisopropylsilyl group the formation of 15c was accomplished as expected. Upon thermally induced 1,7-cyclization of the nitrones 16/26 a multistep rearrangement of the primary cycloallenic intermediates takes place resulting in the formation of the corresponding 6,6,6,5- and 6,6,5,5-ring steroids (17/27 and 18/28) in 55-86% yield. VCH Verlagsgesellschaft mbH, 1996.