Carretero, J. C., De Lombaert, S., & Ghosez, L. (1987). Methyl 3-phenylsulfonyl Orthopropionate - An Efficient Reagent for the Synthesis of Gamma-lactones and Butenolides. Tetrahedron Letters, 28(19), 2135-2138. https://doi.org/10.1016/S0040-4039(00)96063-5 (Original work published 1987)