A new synthetic route to 2-boratanaphthalenes

Double kaliation of 1-isopropenyl-2-methylbenzene (4) and subsequent ring c losure with BCl2(NR2) (R = Me, iPr) provides a new and efficient access to 1,2-dihydro-2-boranaphthalenes 6' and, after metalation with LDA in Et2O or with LiN(SiMe3)(2) in hexane, to lithium 2-boratanaphthalenes 7. The subst ituent at boron may be modified. Treatment of the B-dialkylamino compounds with BCl3 affords the highly reactive beta-chloro derivative 6c', and subse quent methylation with ZnMe2 in toluene affords the B-methyl compound 6d'. The lithium 2-boratanaphthalenes 7 readily form transition metal complexes such as Cp*Fe(4-MeC9H6BNMe2) (9) and Cp*ZrCl2(4-MeC9H6BMe) (10) with hexaha pto coordination of the metal to the boron-containing ring. (C) 1999 Elsevi er Science S.A. All rights reserved.