Aryl trialkylsilyl ketenes:: Acid-catalyzed synthesis from 1-aryl-2-diazo-2-trialkylsilylethanones and their conversion into 3-silyl-1-silyloxyallenes

Aryl-substituted alpha-silyl alpha-diazo ketones are readily transformed into aryl silyl ketenes in the presence of a catalytic amount of triflic acid. Thus, a convenient method to prepare these silyl ketenes becomes available, which combines two steps, silylation of an aryl diazomethyl ketone and acid-induced Wolff rearrangement of the formed a-silyl a-diazo ketone, in a one-pot procedure. It appears that the trialkyl-ammonium salt, which is formed in the silylation step, can also catalyze the Wolff rearrangement, but distinctly more slowly than the proton acid. The silyl ketenes react smoothly with alpha-silyl alpha-diazo ketones to form 3-silyl-1-silyloxyallenes in fairly good yields. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008.