“…Xanthene was proposed to form by intramolecular electrocyclic addition reaction of o- 2 followed by a 1,3 hydrogen shift (Scheme 5B). 15 The photochemical decarbonylation of 2,4,5-trimethylhomogenistic lactone gives the 2-hydroxy-1,3,4-trimethyl- o -quinone methide. 16 The o -thioquinone methide has been generated by decarbonylation of benzothiolactone (Scheme 4B, X = S) and trapped by N-ethylmaleimide.…”