Spiro heterocyclic compounds. V. Synthesis of spiro(homophthalimide-4,4'-(4'H-pyran)) compounds.

Abstract

The reaction of 2-methylphthalonimide (1) with malononitrile gave 4-dicyanomethylene-2-methylhomophthalimide (2) in 95% yield. The Michael reaction of 2 with compounds having an active methylene or methyl group (3a-d) afforded the corresponding spiro [2-methylhomophthalimide-4, 4'-(4'H-pyran)] compounds (4a-d). In contrast, the reaction of 2 with other active methylene compounds (3e-h) afforded only the same product, spiro [2-methylhomophthalimide-4, 1'-(3'-amino-2'-cyano-5', 6'-dihydro-5'-methyl-1'H-pyrano [2, 3-c] isoquinolin-6'-one)] (5), which was found to be produced by the reaction of 2 with homophthalimide in quantitative yield. All the latter reactions can be regarded as the results of retrograde Michael reactions between the reactants 2 and active methylenes (3e-h). By refluxing a methanol solution of 2 in the presence of a basic catalyst, the ringtrasformation product, methyl 1-dicyanomethyl-2-methyl-3-oxo-isoindoline-1-carboxylate (8) was obtained in 80% yield.