Intramolecular carbolithiation of 2,6-dilithio-1,6-heptadienes: an experimental and theoretical study.
2,6-Dilithio-1,6-heptadienes 3 undergo intramolecular carbolithiation in Et(2)O/N,N,N',N'-tetramethylethylenediamine (TMEDA) at the lithiated double bonds to afford 1,2-bis(lithiomethyl)cyclopentenes 5. Reaction of these dianions with electrophiles affords a number of 1,2-difunctionalized cyclopentene derivatives 7-10. The ease of carbolithiation of 2,6-dilithio-1,6-heptadiene (3a) compared to that of 2-lithio-1,6-heptadiene (14) has been studied experimentally. A series of ab initio molecular-orbital calculations on the course of the reaction were carried out and the results were compared to those for the corresponding intramolecular carbolithiation of an isolated double bond. The Li-C interactions found in the transition state by this theoretical study support a carbolithiation pathway for the cyclization of 2,6-dilithio-1,6-heptadienes.
Sanz
Roberto
R
Departamento de Química, Area de Química Orgánica, Facultad de Ciencias, Universidad de Burgos, Pza. Misael Bañuelos s/n, 09001-Burgos, Spain.
Ignacio
José M
JM
Rodríguez
Miguel A
MA
Fañanás
Francisco J
FJ
Barluenga
José
J