Trimethyl(3-Oxido-1-Oxoinden-2-Yl)Ammonium, a New 1,4-Dipolar Ylide

Abstract

Reaction of isobenzofuran-1(3H)-one ( phthalide ) and its derivatives with dimethylformamide dimethyl acetal in the presence of base gives small amounts (c. 10%)¹ of the ylid trimethyl (3-oxido-1-oxoinden-2- yl )ammonium (3). The same compound is formed in higher yield from the corresponding 3-dimethylaminomethyleneisobenzofuran-1(3H)-one. Support for this structure comes from chemical degradation and its mode of synthesis, but relies mainly on X-ray crystallography. The title compound crystallizes as clear prisms in the monoclinic space group P2₁/n with a 15.992(2), b 9.329(4), c 7.112(3)Ǻ, β 90.15(3)° and Z 4. The structural final refinement of a full-matrix least-squares calculation converged with R 0.044 and R_w 0.045.