Oxidation of bicyclic monoterpene ketones with Caro’s acid

Previously unknown seven-membered lactones, (1 R ,1′ R ,5 S ,5′ S )-5,5′-oxybis(1,8,8-trimethyl-2-oxabicyclo[3.2.1]octan-3-one), 2,2-dimethyl-1,6-dioxaspiro[2.6]nonan-7-one, 4-(1-hydroxy-1-methylethyl)-7-methyloxepan-2-one, and (4 R ,4′ R ,7 S ,7′ S )-4,4′-[oxybis(propane-2,2-diyl)]bis(7-methyloxepan-2-one), were synthesized by the Baeyer-Villiger reaction using Caro’s acid as a result of oxidative and skeletal transformations of bicyclic monoterpene ketones, (+)-camphor, (+)-nopinone, and (−)-isocaranone.