Bromine as the Ortho-Directing Group in the Aromatic Metalation/Silylation of Substituted Bromobenzenes

Article abstract of DOI:10.1021/jo034790h

The one-pot metalation/disilylation of selected bromobenzenes bearing electron-withdrawing substituents p-, m-, o-XC₆H₄Br (X = F, Cl, I, CN, CF₃) using 2 equiv of lithium diisopropylamide (LDA) and 2 equiv of chlorotrimethylsilane (TMSCl) was investigated. The best results of disilylation were obtained for para-substituted bromobenzenes, but the regioselectivity of the reaction is strongly influenced by the ortho-directing power of the substituent. On the contrary, the disilylation of metasubstituted bromobenzenes was not efficient or even failed in some cases and hence monosilylated derivatives were isolated as major or sole products. Diverse reactivity was observed for orthosubstituted bromobenzenes, e.g., 2-bromobenzonitrile and 2-bromochlorobenzene, were converted into corresponding disilylated derivatives in a high and moderate yield, respectively, whereas 1-bromo-2-(trifluoromethyl)benzene underwent only monosilylation.