title: Cycloaddition reactions of 1-lithio-1,3-dienes with aromatic nitriles affording multiply substituted pyridines, pyrroles, and linear butadienylimines.
abstract: Fully or partially substituted 1-iodo- or 1-bromo-1,3-dienes could be readily lithiated using t-BuLi or n-BuLi to afford their corresponding 1-lithio-1,3-diene derivatives in quantitative yields. When these in situ generated lithium reagents were treated with organonitriles, depending on the substitution patterns of the butadienyl skeletons, substituted pyridines, pyrroles, and/or linear butadienyl imines were formed in good to excellent yields via N-lithioketimine intermediates. In the cases of 1,2,3,4-tetrasubstituted and 2,3-disubstituted 1-lithio-1,3-dienes, pyridine derivatives or linear butadienyl imines were generally formed depending on the reaction temperatures. When 1,2,3,4-tetrasubstituted 4-halo-1-lithio-1,3-dienes and 1,2-disubstituted 1-lithio-1,3-dienes were treated with organonitriles, pyrrole derivatives or linear butadienyl imines were obtained. Competition between 5-exo and 6-endo cyclization was found to be responsible for the formation of either pyrroles or pyridines. Selective elimination of RLi from the lithiated cyclic N-containing intermediates was observed. The order of elimination was found to be LiCl > Me3SiLi > LiH.
authors.affiliation: Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Bioorganic Chemistry and Molecular Engineering of Ministry of Education, College of Chemistry, Peking University, Beijing 100871, China.
authors.forename: Congyang
authors.initials: C
authors.lastname: Wang
authors.forename: Zhihui
authors.initials: Z
authors.lastname: Wang
authors.forename: Lantao
authors.initials: L
authors.lastname: Liu
authors.forename: Chao
authors.initials: C
authors.lastname: Wang
authors.forename: Guangzhen
authors.initials: G
authors.lastname: Liu
authors.forename: Zhenfeng
authors.initials: Z
authors.lastname: Xi