Steroids Having Fused Heterocyclic Rings

Derivatives of ketones—including oximes, imines, and hydrazones— have served as precursors to oxazoles, although many examples of such conversions are described for steroidal and other fused ring systems. A few examples of steroidal and fused heterocyclic oxazoles and monocyclic analogs are described in this section. 

An elegant one-step d -isoxazoline ring closure from /J-chloro-ketones has been published . Steroid derivatives have been prepared in this manner. A general stereospecific synthesis of zl -thia-zolines from episulfides and nitriles has been reported . The N-ethylbenzisoxazolium cation can combine rapidly with all nucleophilic elements of the first row of the periodic table and at least one member of the second to furnish, mostly in high yield, a variety of unusual intermediates for the synthesis of new benzo-fused heterocyclics, many of them hitherto inaccessible... 

X. Zhang and Z. Sui, Tetrahedron Lett., 44, 3071-3073 (2003). Steroids bearing heterocycles fused to the A-ring are of pharmaceutical interest. Researchers from Johnson Johnson have... 

Steroids bearing heterocycles fused to the A-ring of the steroid nucleus have been of pharmaceutical interest. Zhang at Johnson Johnson has synthesized novel compounds 43 and 44 using a modified Bischler-Mohlau method (PPA, toluene, reflux, 1 h). " ... 

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