INTRAMOLECULAR PHOTOCYCLOADDITIONS OF 6,6'-DIMETHYL-4,4'-POLYMETHYLENEDIOXY-DI-2-PYRONES

Photosensitized reactions of 4,4'-polymethylene-di-2-pyrones 2b-e affo rded [2+2]-cycloadducts 3-5, site-selectively, The selectivity depende d upon the methylene chain length. Namely, the three carbon chain gave a syn head-to-head adduct 3b at the 3,4-position of the 2-pyrone ring , the four to six carbon chains gave syn head-to-head adducts 4c-e at the 5,6-position and/or anti head-to-head adducts 5d,e at the 5,6-posi tion, respectively. The intramolecular cycloaddition mechanism was als o explained from results calculated by means of PM3-CI method.