Thermal Reactions of Epoxyenones and Epoxydienes in the Ionone Series

Article abstract of DOI:10.1002/hlca.19850680503

On flash vacuum thermolysis at temperatures between 390 and 585 deg C, the epoxyenones 1-9 and the epoxydienes 10-12 undergo various types of reactions involving C-C and/or C-O bond cleavage in the oxirane ring.Thus, the compounds 1, 4-9, 11, and 12 were transformed to the divinyl ethers 13, 20, 21, 24, 25, 29, and 38 by a reversible <1,5> homosigmatropic H-shift.On thermolysis of the epoxides 1-12, several products formed via carbonyl-ylide intermediates were also isolated.The extent of the formation of ylide products is clearly related to the conjugating ability of the functional groups neighboring the oxirane.Thus, the epoxides 3, 5, and 7-10 bearing a C(3)=C(4) bond, a 5-oxo function, a 3,4-epoxy or a 3,4-methano group, preferentially underwent reactions via a carbonyl-ylide intermediate.As a further reaction pathway, the epoxides 1-12 undergo cleavage of the C-O bonds of the oxirane, which, however, is presumably an acid-catalyzed rather than a thermal reacion.