Arbusow reaction

Tetra-p-tolylsilane, prepared via Wurtz-coupling of 4-bromotoluene and SiCU, was brominated with NBS according to a procedure described by Drefahl [13] yielding a mixture of the three- and four-fold benzylic bromides la, lb which can be separated by repeated crystallization from acetone. A more convenient way is to convert the crude mixture in a Michaelis-Arbusow reaction to the phosphonates 2a, 2b and to separate these via chromatography (SiOa/ethyl acetate/ethanol). A second Wohl-Ziegler bromination/Michaelis-Arbusow sequence allows one to transform 2a into the tetrahedral 2b in moderate yield. 

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