Stereoselectivity in reactions involving the hydrolysis of acetoxonium ions

Abstract

trans-2-Acetoxy-cis-4-t-butylcyclohexyl tosylate (VIIIa), on treatment with potassium acetate in acetic acid followed by ice–water, gave cis-2-acetoxy-trans-4-t-butylcyclohexanol (XIa) whilst under thermodynamic control it gave an equilibrium mixture of (XIa) and cis-2-acetoxy-trans-5-t-butylcyclohexanol (XIIb) with the latter predominating.

Similarly, trans-2-acetoxy-trans-5-t-butylcyclohexyl tosylate (VIIId) on treatment with potassium acetate in acetic acid followed by ice–water gave cis-2-acetoxy-cis-5-t-butylcyclohexanol (XIIa) whilst under thermodynamic control it gave an equilibrium mixture of (XIIa) and cis-2-acetoxy-cis-4-t-butylcyclohexanol (XIIb).

Although the cleavage of 2β-19-epoxy-5α-cholestan-3α-yl acetate (IV) with boron trifluoride followed by ice–water gave 3α,19-diacetoxy-5α-cholestan-2α-ol (Va), under thermodynamic control the major product was 2α,19-diacetoxy-5α-cholestan-3α-ol (Vb). Similarly, 4α,5α-epoxy-5α-cholestan-3β-yl acetate (XIII) was cleaved with sulphuric acid in acetone followed by cold water to give 4β-acetoxy-5α-cholestane-3β,5α-diol (XVIa) whereas under thermodynamic conditions the major product was 3β-acetoxy-5α-cholestane-4β,5α-diol (XVIb).