Stereoselective reduction of the bioactive 19- nor-clerodane trans-dehydrocrotonin by using sodium borohydride and cerium (III) chloride as a catalyst

摘要

AbstractThe bioactive 19-nor-clerodanetrans-dehydrocrotonin (t-DCTN) is herein used as starting material to afford an epimeric derivative mixture so calledt-DCTN-α and β-OL, which is a diastereoisomeric pair. The stereoselective reduction oft-DCTN was performed in methanol medium by using NaBH4and CeCl3·7H2O which react reducing the C2 carbonyl group on thet-DCTN decalin ring moiety. Thet-DCTN-diastereoisomeric compounds were characterized by chromatographic HPLC analyses and by NMR data. The crystal structure oft-DCTN-α-OL was confirmed employing X-ray diffraction. Additionally, an experimental and theoretical NMR chemical shifts study applied to thet-DCTN diastereoisomeric derivatives lead favorable coefficients of correlation (R?>?0.98) by using B3LYP combined with 6–311++G(d,p) basis set. Furthermore, a modified Gemal and Luche's mechanism in stepwise fashion is proposed. Agreement between theoretical and experimental higher reactivity of NaBH4/Ce3+towards NaBH4was found and the theoretical results explicit the participation of the reaction solvent (methanol) on transition state by using NaBH4unlike that involving NaBH4/Ce3+. It was found that the proposed modified mechanism only occurs in 0.8 eq. of C