Preparation of 1-substituted-3,4-dihydronaphthalene-2-carboxaldehyde N,N-dimethylhydrazones by palladium(0) coupling, and their electrocyclic ring closure

Article abstract of DOI:10.1016/S0040-4020(01)86333-X

1-Bromo-3,4-dihydronaphthalene-2-carboxaldehyde 2 has been converted by three methods, each involving halogen-metal exchange and palladium(0) catalysed cross coupling, into N,N-dimethylhydrazones of 1-aryl- and 1-vinyl-3,4-dihydronaphthalene-2- carboxaldehydes. The N,N-dimethylhydrazone 10 of the aldehyde 2 undergoes efficient bromine-lithium exchange with butyllithium, as does 2-bromobenzaldehyde N,N-dimethylhydrazone 17. The dimethylhydrazones of 1-vinyl-3,4-dihydronaphthalene-2-carboxaldehydes were not isolated by underwent electrocyclic ring closure followed by loss of dimethylamine in solution to give 5,6-dihydrobenz[f]isoquinolines. 1-Aryl-3,4-dihydronaphthalene-2- carboxaldehyde N,N-dimethylhydrazones also cyclised in the same way when subjected to vapour phase pyrolysis.