Sodium cyanoborohydride-tributyltin chloride

Tributyltin hydride, 316 Zinc iodide, 280 From alkyl halides Lithium aluminum hydride-Ceri-um(III) chloride, 159 Palladium catalysts, 230 Sodium cyanoborohydride-Tin(II) chloride, 280 From alkyl sulfonates Lithium triethylborohydride, 153 From thiols... 

Catalytic procedures (introduced by Kuivila and Menapace92) are easier to conduct and the tin hydride concentration is more easily controlled. A catalytic amount of tributyltin hydride or tributyltin chloride is mixed with the radical precursor, the alkene acceptor and a stoichiometric quantity of a coreductant such as sodium borohydride93 or sodium cyanoborohydride.29 Over the course of the reaction, the borohydride continuously converts the tin halide to tin hydride. The use of the catalytic procedure is probably restricted to halide precursors (tin products derived from other precursors may not be reduced to tin hydrides). This method has several advantages over the standard procedures (i) it is simple to conduct (ii) most functional groups are stable to the coreductants (especially sodium cyanoborohydride) (iii) the tin hydride concentration is known, is stationary (assuming that the tin halide is rapidly reduced to tin hydride), and can be varied by either changing the concentration of the reaction or the quantity of the tin reagent (10% is a typical value, but lower quantities can be used) and finally, (iv) the amount of tin hydride precursor that is added limits the amount of tin by-product that must be removed at the end of the reaction. 

Generating tin hydride in situ by using a catalytic amount of tributyltin chloride and sodium cyanoborohydride [24] did not solve the problem. Although this method inherently produces the desired low concentration of n-BujSnH to promote cyclization over direct reduction of the starting material and reduces drastically the amount of tin residue, a displacement reaction between solvent and the benzylic hydroxyl group takes place. Eventually, the best method was the use of high dilution conditions at approximately 70 °C in benzene followed by the KF workup. 

Perhaps the interplay between sugar amino acids and a-amino acids is more clearly demonstrated in the synthesis of a-D-glucosyl-(i )-alanine reported by Axon and Beckwith [33]. In the reaction, (27 )-methyleneoxazolidinone was treated with 2,3,4,6-tetra-O-acetyl glucosyl iodide in the presence of sodium cyanoborohydride and tributyltin chloride to give the a-C-glycoside in 88% yield (Fig. 15). 

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