In the mol-ecule of the title compound, C(9)H(8)ClNO(4), an intra-molecular C-H⋯O hydrogen bond results in the formation of a planar five-membered ring, which is nearly coplanar with the adjacent six-membered ring, the rings being oriented at a dihedral angle of 4.40 (3)°. In the crystal structure, inter-molecular C-H⋯O hydrogen bonds link the mol-ecules.

protonation of the reactive intermediate produced in the  reaction between trimethyl phosphite and dimethyl acetylenedicarboxylate or diethyl acetylenedicarboxylate by resorcinol, 5-methylresorcinol, 2,5-dihydroxyacetophenone, 4-chloro-2-methylphenol, 4-chloro-3,5-dimethy-lphenol, 4-hydroxypyridine, 2-hydroxypyridine, 3-hydroxypyridine, or 8-hydroxyquinoline leads to vinylphosphonium salts, whi...

Protonation of the reactive intermediate produced in the  reaction between trimethyl phosphite and dimethyl acetylenedicarboxylate or diethyl acetylenedicarboxylate by resorcinol, 5-methylresorcinol, 2,5-dihydroxyacetophenone, 4-chloro-2-methylphenol, 4-chloro-3,5-dimethy-lphenol, 4-hydroxypyridine, 2-hydroxypyridine, 3-hydroxypyridine, or 8-hydroxyquinoline leads to vinylphosphonium salts,...

The title compound, C(10)H(12)ClNO(3), crystallizes with four independent mol-ecules in the asymmetric unit which are linked by inter-molecular N-H⋯O hydrogen bonds.