Oxidative benzylic substitution of azulene-1-azo(4 '-methylbenzene)s

Treatment of azulene-1-azo(4'-methylbenzene) with position 3 blocked by dif ferent substituents X (2) or by steric hindrance (3), with FeCl3 in benzene , resulted in the substitution of one or two benzyl hydrogens by phenyl gro ups. Starting either from 2 (X=CH3, Cl) or from 3, triarylmethane derivativ es 7 or 10 and corresponding alcohols 9 or 11 are the main separated produc ts while starting from 2 (X=OCH3), diarylmethanol 8 as well as the related benzophenone and ether, 13 and 14, respectively, are isolated as major prod ucts. Diphenylmethane and triphenylmethane also result from almost all reac tions. Conversion of the starting materials was good and the products that were separated and characterised are obtained in 43.5-60.5% overall yields. Single-electron transfer oxidation was thought to be the first reaction st ep with the generation of the radical cation 2(.+). As a result of the prot on and electron transfer or hydrogen atom transfer from 2(.+), the cation 1 6 with some benzylic character was formed. The cation 16 alkylated benzene in the subsequent reaction and diarylmethane derivatives were formed. A sim ilar reaction pathway can be proposed for triarylmethane products generatio n.