Chiral phthalimido thioxo-stabilised phosphonium ylides, prepared starting from (S)-alanine and (S)-phenylalanine, undergo intramolecular Wittig reaction upon pyrolysis leading to the previously unknown pyrrolo[2,1-a]isoindol-5-one-2-thiones, rather than the expected P to S migration of a phenyl group. Pyrolysis of thioxo-stabilised ylides with three different groups on phosphorus gave some evidence of the required migration, but led in one case to unexpected formation of a 1,4-benzoxaphosphininium salt.
Aitken, R. A., Barker, G., Cleghorn, L. P., Reid, E. J., & Roberts, S. S. (2014). Formation of Unexpected Heterocyclic Products from Pyrolysis of Thiocarbonyl Stabilised Phosphonium Ylides. Heterocycles, 88(2), 1135-1147. https://doi.org/10.3987/COM-13-S(S)70