Higher selectivity at higher temperatures! Effect of precursor stereochemistry on diastereoselectivity in radical allylations. Insight into the role of the Lewis acid

A derailed investigation of the effects of Lewis acid, temperature, and tra pping efficiency of functionalized allylstannanes on diastereoselective rad ical allylation reactions of alpha-bromoxazolidinone imides 1 and 2 was con ducted. Results indicate that despite the addition of Lewis acids, a bident ate chelated radical intermediate 21 may be accessible from only one diaste reomer of starting material due to steric interactions in 20 that are not p resent in chelated intermediate 17. It is shown that application of the app ropriate Lewis acid, increasing temperatures, and slower allylstannane trap s all facilitate formation of 21. Thus highly stereoselective radical allyl ations (>50:1, Tables 2 and 3) can be performed at room temperature as well as low temperatures.