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The [3 + 2] cycloaddition reaction of 2-arylthiocarbamoylbenzimidazolium, -imidazolinium, and -triazolium inner salts(the ambident C-C-N and C-C-S 1,3-dipoles derivedfrom carbenes) with ketenes proceeded efficiently in a highlysite-selective manner to produce the C-C-N cycloadditionproducts benzimidazoline-, imidazolidine-, or triazoline spiro-pyrrolidones in 58-93% yields. Theoretical calculationsuggests a stepwise mechanism for the reaction and indicatesthat the C-C-N cycloaddition of the dipoles with ketenesis both a dynamically and thermodynamically favoredreaction pathway. Their easy availability, high reactivity, andreaction selectivity render the benzimidazolium, -imidazolinium, and -triazolium inner salts powerful and versatile 1,3-dipoles in the construction of novel spiro heterocyclicsystems, which are not easily accessible by other methods.
