Nitrones-III: Reaction of 3,4-dihydroisoquinoline n-oxide with phosphonoylids

Reaction of 3,4-dihydroisoquinoline N-oxide 1 with diethyl cyanomethylphosphonate 2 gave the enaminonitrile 1-cyanomethylene-1,2,3,4-tetrahydroisoquinoline 3. Reaction of 1 with trialkyl phosphonoacetate 4 gave 5, the fused aziridine derivative 7 - exo - carbethoxy -1 - aza - 4,5 - benzo - bicyclo[4.1.0]heptene - 4, and the enaminoester 1-carbalkoxymethylene-1,2,3,4-tetrahydroisoquinoline 6. The ratio of 5:6 depends on the reaction conditions. While using 1,2-dimethoxyethane the aziridine 5 is the major product; using alcoholic solvents the yield of 6 increases at the expense of 5 with increasing acidity of the solvent.