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Chemoselective construction of novel steroid derivatives
Luigino Troisi1, Saverio Florio, Catia Granito
1Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali, University of Lecce, Via Prov.le Lecce, Monteroni, I- 73100 Lecce, Italy. luigino.troisi@unile.it
Abstract:
Alpha-halo-alpha-heteroarylalkyllithiums, generated by deprotonation of the corresponding halides, when added promptly to steroids with C=O or C=NR groups, lead to epoxides and aziridines. The reactions are regio- and stereoselective; in fact, in the presence of more than one C=O group, the oxido or aziridino functions are formed uniquely at the C=O of C-17 (or C-20 depending on its position in the starting molecule), and the C-20(R) stereoisomer is often the only product isolated. Protection of the hydroxyl group present on several considered steroids was required, and it was accomplished through derivatization in acetyl, ether, or lactone.