title: Highly efficient and site-selective [3 + 2] cycloaddition of carbene-derived ambident dipoles with ketenes for a straightforward synthesis of spiro-pyrrolidones.
abstract: The [3 + 2] cycloaddition reaction of 2-arylthiocarbamoyl benzimidazolium, -imidazolinium, and -triazolium inner salts (the ambident C-C-N and C-C-S 1,3-dipoles derived from carbenes) with ketenes proceeded efficiently in a highly site-selective manner to produce the C-C-N cycloaddition products benzimidazoline-, imidazolidine-, or triazoline spiro-pyrrolidones in 58-93% yields. Theoretical calculation suggests a stepwise mechanism for the reaction and indicates that the C-C-N cycloaddition of the dipoles with ketenes is both a dynamically and thermodynamically favored reaction pathway. Their easy availability, high reactivity, and reaction selectivity render the benzimidazolium, -imidazolinium, and -triazolium inner salts powerful and versatile 1,3-dipoles in the construction of novel spiro heterocyclic systems, which are not easily accessible by other methods.
authors.affiliation: Chemistry Department, Beijing Normal University, Beijing 100875, China.
authors.forename: Jia-Qi
authors.initials: JQ
authors.lastname: Li
authors.forename: Rong-Zhen
authors.initials: RZ
authors.lastname: Liao
authors.forename: Wan-Jian
authors.initials: WJ
authors.lastname: Ding
authors.forename: Ying
authors.initials: Y
authors.lastname: Cheng