Crystal structure of a cyclopentenylidenephosphorane isolated from the reaction of tri-p-tolylphosphine and dimethyl acetylenedicarboxylate

Abstract

The product from the reaction of tri-p-tolylphosphine and excess of dimethyl acetylenedicarboxylate has been shown by X-ray crystallography to be trimethyl 3-methoxy-4-oxo-5-(tri-p-tolylphosphoranylidene)cyclopentene-1,2,3-tricarboxylate. The crystals were monoclinic with a= 17·60(1), b= 11·439(6), c= 31·67(2)Å, β= 107·11(2)°, and Z= 8 in space group C2/c. The refinement was terminated at an R factor of 14·8% by use of isotropic temperature parameters and with toluene residues treated as rigid groups. The PC bond of length 1·728(8)Å is part of a conjugated system involving CC in the cyclopentenyl ring, the 2-methoxycarbonyl substituent, and the carbonyl group at C(4). Some bond angles are larger than normal owing to mutual repulsion of adjacent substituents of the cyclopentenyl ring.