Nucleophilic substitution on α-mesyloxy-O-alkyloximes—II. Enantiospecific synthesis of 2-(imidazol-1-yl)-1-cyclohexyl-3-phenylpropan-1-one O-alkyloximes
作者:Antonio Giordani、Alberto Carera、Vittorio Pinciroli、Paolo Cozzi
DOI:10.1016/s0957-4166(96)00506-x
日期:1997.1
An enantiospecific synthesis of (S)- and (R)-(E)-5-[1-cyclohexyl-3-phenyl-2(imidazol-1-yl)propylidene]aminooxypentanoic acids 2 using homochiral phenylalanines as starting material is described. Protected alpha-hydroxy-N,O-dimethylamides 4, obtained from alpha-hydroxyacids 3 were coupled with 1-cyclohexenyllithium to afford alpha,beta-enones 5, which were in turn converted to alpha-hydroxyketones 6. Configurational liability of compound 11, prompted us to attempt imidazole introduction on the alpha-hydroxy-O-alkyloxymes 12 which proved to be configurationally more stable. Thus nucleophilic substitution on alpha-mesyloxy-O-alkyloxymes 14 led, after ester removal, to homochiral compounds 2. The use of hydrogenolysis for 14b deblocking provided 2a with 97% ee. Considerations on the stereochemical outcome of this hitherto undescribed nucleophilic substitution on alpha-mesyloxy-O-alkyloxymes are reported. (C) 1997 Elsevier Science Ltd.