Novel synthesis of indazoles from (eta(6)-arene)tricarbonylchromium complexes

Indazole chromium complexes and some of its derivatives were synthesised by two strategies: (1) by cyclisation of [eta(6)-2-(2'-phenylhydrazine)-1,3-d ioxolane]tricarbonylchromium (2) in acidic conditions which was converted i nto sigma-complex (ll), (2) by thermolysis of Cr(CO)(6) with 1-bis(trimethy lsilyl)methylindazole (3) and 2-bis(trimethylsilyl)methyl-3-trimethyl-silyl indazole (4), using bulky protecting groups at N(1) or simultaneously at N( 2) and C(3), to afford [eta(6)-1-bis(trimethylsilyl)methylindazole]tricarbo nylchromium (14) and [eta(6)-2-bis(trimethylsilyl)methyl-3 -trimethylsilyli ndazole] tricarbonylchromium (15), respectively. The deprotonation of compl ex 14 followed by electrophilic quench occurs at the C(4) and C(7) position s in a ratio of 3:1 and with complex 15 the deprotonation was completely re gioselective at the C(7) position. The position of this substitution was co nfirmed by n.O.e. difference spectroscopy and X-ray crystal structure deter mination of the [eta(6)-2-bis(trimethylsilyl)methyl-7-methyl-3-trimethylsil ylindazole]tricarbonylchromium (5). These complexes were decomplexed to pro duce new substituted indazole derivatives in good yield. (C) 2000 Elsevier Science S.A. All rights reserved.