(3-Alkoxycarbonyl-2-oxo-propylidene)triphenylphosphorane reacts with 1,2-diacylethylenes to give cyclopentenones in a single operation. Use of a chiral acylmethylenemalonate led to formation of optically active cyclopentenone in a highly diastereoselective fashion.
Hatanaka, M., Ishida, A., Tanaka, Y., & Ueda, I. (1996). Single-step synthesis of cyclopentenones from (3-alkoxycarbonyl-2-oxo-propylidene)triphenylphosphorane and 1,2-diacylethylenes. Tetrahedron Letters, 37(3), 401–404. https://doi.org/10.1016/0040-4039(95)02186-8