BETA-FUNCTIONALIZED RADICALS IN ORGANIC-SYNTHESIS - 2-ACYLOXYALKYL RADICALS FROM 2-ACYLOXYALKYL IODIDES BY THE TIN ROUTE

The reaction of iodoesters 1a-c with electrophilic olefins 2a-d and in situ generated tributyltin hydride (from a substoichiometric amount of tributyltin chloride and an excess of sodium borohydride) in the presence of a catalytic amount of AIBN in ethanol at 0 to 20 degrees C yields the expected coupling products 3aa-3cd. Products 4 resulting from an iodine/hydrogen exchange are also obtained as by-products in variable amounts. The stereochemistry of the coupling reaction is studied: starting from trans-2-iodocyclohexyl acetate (1d) and methyl acrylate (2a) a 1/3 mixture of the corresponding cis/trans diastereoisomers is obtained. This result indicates that the corresponding radical coupling is not stereospecific.