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Reductive Properties of (4R,5R)-2,2-Dimethyl-1,3-Dioxolane-4,5-Bis(Diphenylmethylstannane)
Abstract: Chiral organotin halides and hydrides have been widely investigated as chiral inductors for asymmetric synthesis. They have been used in a variety of reactions such as ketone reduction, alpha bromo esters reduction, radical cyclization of aldehydes, among others. Several chiral organotin hydrides are reported in literature, but to the best of our knowledge none of them have two tin hydrides moieties. So that, we were interested in the synthesis of (4R,5R)-2,2-dimethyl-1,3-dioxolane-4,5-bis(diphenylmethylstannane). The synthesis of this tin hydride was achieved in six steps starting from dimethyl-(L)-tartrate. The first attempt was to apply the new chiral organotin hydride in the reduction of prochiral ketones. We faced with several disadvantages in this reaction because stoichiometric amounts of the tin hydrides were needed to reduce ketones, and despite of this, the tin hydride was unable to reduce them completely. We decided to focus on the reduction of alpha bromo esters, inspired in the work of Metzger and co-workers. Alpha bromo esters can be reduced by using an organotin halide and NaCNBH3 as a source of hydride. In this condition, the organotin halide is used in catalytic amount. We permormed the reactions with 1, 5 and 10 mol% the organotin halide and the last conditions allowed the reaction to complete.
Keywords: Organotin hydrides; alpha bromo esters reduction