Spiro Heterocyclic Compounds. IV. Synthesis of Spiro [oxindole-3, 4'-(2', 3'-dihydro-4'H-pyran)] and Spiro [oxindole-3, 4'-(1', 4'-dihydropyridine)] Compounds

Abstract

The Michael reaction of 3-(carboethoxy-cyano) methyleneoxindole (Ia) or 3-dicyanomethyleneoxindole (Ib) with active methyl groups, e.g., acetophenone and acetone, afforded, the corresponding normal Michael adducts (IIa-c). The reduction of IIa with NaBH₄ gave the spiro [oxindole-3, 4'-(2', 3'-dihydro-4'H-pyran)] compound (III), which on reaction with diazomethane afforded two methoxy derivatives (IVa, b) diastereomeric at C-2' of the 2', 3'-dihydropyran ring. The reduction of IIb, c with NaBH₄ gave similar spiro compounds (V-VI), which gave similar diastereoisomers, Va, b and VIa, b, respectively. Refluxing of IIc with NH₂OH gave the spiro [oxindole-3, 4'-(1', 4'-dihydropyridine)] compound (X). When the same reaction was carried out at 0°, compound (IX), the precursor of X, was obtained.