Mechanistic aspects of the Diels-Alder reaction between (E)-N-benzylidene-2,2-difluoro-1-phenylethenamine and 2-vinyl pyridine: A molecular electron density theory study

A MEDT study is carried out on dehydrofluorination of benzyltrifluoromethylketimine (BFK) to (E)-N-benzyli-dene-2,2-difluoro-1-phenylethenamine (BFPA), and the Diels-Alder (DA) reaction of BFPA with 2-vinylpyridine (2VP), which has been performed experimentally by Fu and co-workers. PES analysis indicated that in the dehydrofluorination reaction, the deprotonation of BFK is the RDS in the presence of 2,2,6,6-tetramethylpiper-idine (TMP), and the presence of 2,2,6,6-tetramethylpiperidinium ion generated in the deprotonation step, is essential for defluorination. In consistent with the experimental work, it was found that the formation of cis ortho disubstituted cycloadduct from the DA reaction is more favorable kinetically. The high activation barriers rationalize the performing of reactions in harsh conditions. The ELF analysis suggested that the DA reaction takes place through a two-stage one-step mechanism via the coupling of pseudoradical centers. IGM analysis confirmed the endo stereoselectivity predominance of the reaction. Finally, it was found that the BF3 Lewis acid makes the reaction unfavorable.