Synthesis of some 2′‐(3‐Oxopregn‐4‐en‐20‐yl)oxazolidines and ‐thiazolidines

Abstract

Previous efforts to construct oxazolidine' -4 ) or thia~olidine'-~) rings on steroid skeleton led to pharmacologically active compounds. With one exception:) all these examples involved a ring keto group, giving rise therefore to spiranic structures. oxazolidines and thiazolidines attached to the steroidal side chain by bringing 3-0x0-pregn-4-ene-20(3-carboxaldehyde (1) to react with various aminoalcohols and aminothiols.The condensations of 1 with the amino alcohols were effected by azeotropic removal of the water liberated under conditions indicated in Table 1 .') Free forms of 2 and 8 were found to be unstable, but could be isolated and characterized in their corresponding N-acetyl derivatives 7 and 9. In the nmr spectrum 2 e h b i t e d a doublet at 6 7.39 ppm (J = 7 Hz 1/2 H) attributable to the aldiminic proton and a broad signal at S 4.25 ppm (1/2 H) assigned t o H 2' of the oxazolidine ring. From these, and from the presence of two resonances attributable to (2-18 methyl group protons in the nmr spectrum of 2 it was inferred that the product from 2-aminoethanol is a mixture of ring-chain tautomers in a ratio of approximately 1 : 1. The spectra of oxazolidines, containing tertiary nitrogen atoms do not show signals around 4.2 ppm. In analogy to To extend existing knowledge in this area, we deemed it of interest to prepare new