Asymmetric Synthesis Of Optically Active Azidoalcohols, Cyclic Carbonates And Epoxide Derivatives By Cobalt(Salen) Complexes

The development of chiral catalysts that are not only enantioselective and high yielding but also useful from a practical standpoint persists as a challenging goal in asymmetric synthesis. In the ideal case, a chiral catalyst could be readily available or easily synthesized on any scale and should display both high enantioselectivity and reactivity (turnover frequency).In this study, we have synthesized homogeneous and heterogeneous chiral dinuclear Co(salen) complexes and demonstrated their catalytic activity and selectivity for the asymmetric ring opening of terminal epoxides and asymmetric cyclization of chlorohydrins to afford both recovered epoxides and corresponding products in one step. Optically active Cobalt (salen) complexes show very high catalytic activity and enantioselectivity for the asymmetric ring opening of terminal epoxides using HN3 as azide source. It provides a facile and practical synthetic route to a wide range of chiral nonracemic 1, 2-azido alcohols and related compounds in one-pot synthesis with excellent selectivity and yield under mild conditions. After screening the catalysts, The dimeric catalysts exhibit not only remarkablely enhanced reactivity but also significantly higher enantioselectivity relative to monomeric catalysts. Organic solvent was found to have an crucial effect on the reaction rate of the present study, tert-Butyl methyl ether being found to be the most favorable solvent among CH₂Cl₂, CHCl₃ and THF under the same condition.Chiral (salen)Co complex bearing lewis acid of group 13 metal chloride itself or in the presence of alkali metal salts, quaternary ammonium halides, ionic liquids are effective catalyst systems for the cycloaddition of carbon dioxide to epoxide with excellent activity and enantioselectivity. The anions, cations and the catalytic amount of cocatalysts could play a significant role in determining the system's selectivity in addition to the activity. For the asymmetric cyclization of 1, 3-dichloro-2-propanol (DCP), A series of parallel experiments have been done using different bases, solvents and different ratios of the reactants. For the purpose of comparison, asymmetric cyclizations of racemic 1-chloro-2-propanol and...