Addition of stannylated carboxylic acid derivatives to the carbonyl group of aldehydes

Abstract

Addition reactions of Bu 3SnCH 2COOEt with PhCHO at 75°C in the presence of Bu 3SnI and reactions of Et 3SnCH 2X (X = COOEt, CN, CONMe 2) with benzaldehyde, cinnamaldehyde and furfural at 20°C in DMSO in the presence of Me 4NF (2 mol %) were investigated. Adducts obtained in high yield in these reactions readily undergo hydrolysis (when treated with aqueous KF) and acetolysis (when treated with AcCl) with quantative formation of 3-hydroxy and 3-acetoxy derivatives of esters, nitriles and amides. We show that interaction of Et 3SnCH 2COOEt with the above-mentioned aldehydes and isovaleraldehyde in the presence of equimolar amounts of Et 4NCl in CH 2Cl 2/HMPTA ( 10 1 ) at 20°C followed by treatment of the reaction mixture with AcCl readily gives 3-acetoxyesters. Reactions of PhCH(SnMe 3)COOEt with acrolein, crotonaldehyde and cinnamaldehyde and the hydrolysis of the obtained adducts lead exclusively to 1,2-addition products, these reactions are virtually non-stereoselective. The reaction of PhCH(SnMe 3)COOEt with benzaldehyde at 20°C in DMF, CH 2Cl 2 or without solvent gives mainly threo-ethyl(2,3-diphenyl-3-hydroxy)propionate whereas at −78°C in CH 2Cl 2 in the presence of BF 3 · Et 2O erythro isomer is mainly formed. The data obtained are discussed within the framework of the mechanism involving the participation of the O-isomer CH 2C(OEt)OSnR 3. This active intermediate is formed via metallotropic rearrangement of the starting organotin compound.