Functionalized Benzylic Magnesium Reagents through a Sulfur-Magnesium Exchange

摘要

The preparation of benzylic magnesium compounds has been studied extensively because of the high reactivity and synthetic utility of these reagents.[1] Although the direct insertion of magnesium into benzylic bromides is possible, the formation of Wurtz homocoupling products complicates this approach, especially when electron-rich benzylic halides are used as substrates. Herein, we report the preparation of functionalized benzylic magnesium reagents by using a new sulfur-magnesium exchange reaction.[2], [3] We prepared o-(o-iodophenyl)phenylthio derivatives[4] of type 1 because a range of functionalized benzylic derivatives are readily available through the reaction of thiosulfonates 2 with the monomagnesium derivative 3 of 2,2-diiodobiphenyl (4) (Scheme 1).[5], [6] The required thiosulfonates 2 were prepared either by the reaction of PhSO2Na with disulfides[7] or by the reaction of PhSO2SNa with various benzylic halides in N,N-dimethylformamide[8] (see Supporting Information). Alternatively, the benzylic o-(o-iodophenyl)phenylthio derivatives 1 can also be synthesized from 4 through the two-step preparation of the chloromethyl thioether 5, which was obtained in 72 % overall yield.[9] Treatment of 5 with various aryl copper derivatives (ArCu, 1.5 equiv; -40 ?CRT, 20 h), in the presence of Bu4NI (1.0 equiv), directly produces the benzylic thioethers 1 in satisfactory yields.