Intramolecular Carbolithiation of 2,6‐Dilithio‐1,6‐heptadienes: An Experimental and Theoretical Study

Abstract 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 ( 3 a ) 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.