A pseudopericyclic [3,5]-sigmatropic rearrangement of a coumarin trichloroacetimidate derivativeElectronic supplementary information (ESI) available: Experimental section for synthesis and pyrolysis of 2 and 3; 1H- and 13C-NMR spectra for 3 and 8; X-ray crystallographic details for 8; computational details and Cartesian coordinates for all calculated structures; full citation for ref. 27 (PDF). CCDC 1568018. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c7o

Thermolysis of a coumarin trichloroacetimidate yields a single rearrangement product. The proposed mechanism is a pseudopericyclic allowed (Woodward-Hoffman forbidden) [3,5]-sigmatropic rearrangement to form the corresponding amide followed by a sigmatropic [1,5]-hydrogen migration. Transition state calculations at the B3LYP/6-31G(d,p) level support this mechanism and suggest the selectivity is influenced by the stability of the intermediates. A Woodward-Hoffmann forbidden, eight-centered transition state leads to the sole product of a pentadienyl imidate rearrangement.