A route to 1, 4-prop[2]enoisoquinolines via the cyclisation of triene-conjugated nitrile ylides~1

摘要

Triene-conjugated nitrile ylides of the types 18 and 20 with #alpha#, #beta# aromatic and #gamma#, #delta#; #epsilon#, #xi# olefinic unsaturation undergo intramolecular cyclisation on to the #gamma#, #delta# bond via a formal 1, 1-cycloaddition reaction to give respectively endo- and exo-1-alkenylcyclopropa[c]isoquinolines 23 and 25 as primary products. The endo-isomers 23 rearrange spontaneously at 0 deg C to give 1, 4-dihydro-1, 4-prop[2]enoisoquinolines 24 via an aza-Cope reaction. The exo-isomers 25 give the same product on heating at 70 deg C via equilibration with the endo form 26 as the primary step, provided that the concentration of the latter at equilibrium is not strongly disfavoured by the steric effect of substituents R~1 and R~2. If it is then an alternative rearrangement also occurs to give the azabenzo[3, 4]barbaralane derivative 29.