2-BORAINDANES AND 2-(DIALKYLAMINO)-2-BENZOBOROLE DIANIONS

ortho-Xylene reacts with the Lochmann-Schlosser base to produce a mixture of the potassium derivatives K2[1,2-C6H4(CH2)2] (2) and K[2-MeC6H4CH2] (3). Condensation of 1 + 2 with BCl2(NR2) (R = Me, Et, iPr) affords 2-(dialkylamino)-2-boraindanes (1a-c) (50%). Treatment of 1a, b with LiTMP/TMEDA in THF yields dilithio derivatives [Li(tmeda)]2[C6H4(CH)2BNR2] (8a, b) (40%) which show tripledecked structures consisting of an aromatic 10pi-electron 2-benzoborole dianion and two [Li(tmeda)]+ units facially bound to the borole ring. 1 a reacts with HCl/Et2O/hexane to give C6H4(CH2)2BCl . OEt2 (1d . OEt2) (76%) which decomposes in vacuo to give the chloro derivative 1d. The methyl derivative C6H4(CH2)2BMe (1e) is obtained from 1a by treatment with LiMe/Et2O at -78-degrees-C and subsequently with HCl/Et2O at -78-degrees-C (41%). 1a, b react with MeOH at -78-degrees-C to give solid adducts C6H4(CH2)2BOMe . NHR2 (12a, b) while 1c affords C6H4(CH2)2BOMe (1f). Subsequent ring-opening produces 2-MeC6H4CH2B(OMe)2 (13). With the exception of 1b the 2-boraindanes 1 are crystalline solids. The silylation of the 2-benzoborole dianions and various (2-methylbenzyl)borane derivatives is also described.