Trimethylsilylimidazoles have received much attention because of their synthetic and application challenges. 1,2 Moreover, the trimethylsilyl group is characterised by chemical inertness and a large molecular volume, which makes it useful in a number of applications. [3][4][5] Trimethylsilylimidazoles are used as silyl protecting and derivatisation reagents, 6,7 reducing agents, 8 in cross-coupling chemistry 9 and to stabilise α-carbanions and β-carbocations. 9 Previously we studied the reactions of the active phosphacumulenes, phosphallenes, stabilised phosphonium ylides, Lawesson and Japanese reagents to prepare new heterocyclic and homocyclic compounds containing phosphorus moieties of industrial and biological interest. [10][11][12][13][14][15][16][17][18][19]
Results and discussionWe now report the reaction of 1-trimethylsilyl-1H-imidazole (1) with (N-phenyliminovinylidene)triphenylphosphorane (2a), (2-oxovinylidene)triphenylphosphorane (2b), hexaphenylcarbodiphosphorane (5), Lawesson's reagent (8a) and Japanese reagent 9a (Schemes 1-4). The phosphacumulene ylides (2a and 2b) can each be described by the resonance structures 2A and 2B (Scheme 1). Accordingly, treatment of 1 with 1 equiv. of 2a in dry toluene led to the formation of imidazolesilylphosphoranylidene aniline 3a. When the reaction was performed in hot THF and the product was chromatographed on silica gel, the new compound imidazolephosphoranylidene aniline 4a was isolated. Adduct 3a was formed by nucleophilic attack of 2a on 1 and fast exchange