The ring opening
of 2α,3α- and 2β,3β-epoxy-5α-androstan-17-one
with halide reagents (AlCl3, TMSCl, LiCl, and LiBr) was
investigated using imidazolium ionic liquids in the dual role of solvent
and catalyst. The application of the ionic liquid was shown to result
in an increase in the amount of the unusual diequatorial halohydrins
especially at temperatures above 100 °C. With a careful choice
of reaction conditions, the latter derivatives could be produced with
43–96% selectivity depending on the nature of the halide ion.
Moreover, the usual diaxial products could also be isolated in 70–85%
yields by a proper change in the reaction conditions. The reusability
of the ionic liquid was demonstrated in both types of reactions. The
structures of the products were proved unequivocally by nuclear magnetic
resonance (NMR) measurements including two-dimensional (2D) techniques
as well as high-resolution mass spectrometry (HRMS). Based on quantum
chemical calculations, the effect of the ionic liquid could be explained
by the stabilization of the transition state leading to the diequatorial
product.
In the catalytic addition of thiols to 16‐dehydropregnenolone fourteen thioethers were prepared via thiol‐Michael addition reaction in the presence of different aliphatic and aromatic thiols as reagents. [HDBU][OAc] was proved to be an efficient catalyst and solvent providing thioether derivatives in good to excellent yields. The ionic liquid could be reused for five times without noticeable loss of activity. The structures of compounds were confirmed by 1H‐, 13C NMR and IR spectroscopy and mass spectral analysis. A series of these pregnenolone derivatives were evaluated for their cytotoxic activity on breast cancer (MDA‐MB‐231, MCF7) cell lines.
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