Efficient Control of the Stereoselectivity in Reactions of 2-Oxy-Substituted Benzylic Radicals

The stereoselectivity in reactions of 2‐oxy‐substituted radicals of type B was investigated. As expected, minimization of allylic 1,3‐strain was the major controlling factor. Under standard conditions, only a modest level of stereoselectivity was observed. E.g., deuteration of the benzylated radical (R1 = benzyl) gave diastereoisomer ratios ≤ 2:1. Use of a bulky protective group on the O‐atom (R1 = (t‐Bu)Ph2Si) enhanced slightly the selectivity (ratio 4.1:1). However, a dramatic increase of the stereoselectivity (ratio 13:1) was obtained, when the reaction was performed with the free alcohol after treatment with bulky methylaluminium bis(phenoxide) derivatives (methyl‐aluminium bis[2,6‐di(tert‐butyl)‐4‐methylphenoxide] (MAD) and methylaluminium bis(2,6‐diphenylphenoxide) (MAPH)).