PREPARATION OF 1-SUBSTITUTED-3,4-DIHYDRONAPHTHALENE-2-CARBOXALDEHYDE N,N-DIMETHYLHYDRAZONES BY PALLADIUM(0) COUPLING, AND THEIR ELECTROCYCLIC RING-CLOSURE

I-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 NN-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 but 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 NN-dimethylhydrazones also cyclised in the same way when subjected to vapour phase pyrolysis.