Synthesis of 6-Bromo-3a,4-dihydrobenzo[f]isoindolinium Bromides and Their Aqueous-Alkaline Cleavage

Cyclization of allyl[3-(4-bromophenyl)prop-2-ynyl]ammonium bromides under basic catalysis conditions, unlike their propargyl analogs, occurs under heating of the reaction mixture at 90–92°C. Cyclization, which is the main reaction route, is accompanied by rearrangement-cleavage to form 1-allyl- p -bromocinnamaldehyde. A favorable effect of the substituents on the nitrogen atom and the presence of the bromine atom in the 4 position of the aromatic ring on the cyclization and rearrangement-cleavage reactions is established.