Solid-state and solution photocycloadditions of 4-acyloxy-2-pyrones with maleimide

Effect of Ring Size on theExo/EndoSelectivity of a Thermal Double Cycloaddition of Fused Pyran-2-ones

“…The presented results are very interesting, as it was not possible to anticipate (at least not from previous literature reports) that the interplay between the size of the ring ( 1A , B vs. 1C ), the type and size of the substituent on the cyclic dienophile 2 (NR 1 vs. O), and the stabilities of products would have such a strong effect on the stereo outcome of these thermal cycloadditions. Similar exo , endo products were so far obtained only under photochemical conditions; however, an effect of the structure of the starting compounds on the stereo outcome of the cycloaddition was not reported; only the effects of various reaction conditions were presented.…”

Organic photochemistry

“…22 Photochemistry in the solid state is important in stereoselective reactions, and photosensitized reactions of 4-acyloxy-2-pyrones with maleimide gave the endo-endo double-[4 + 2] cycloadducts 27 (R = Me, Ph, Ar) with high stereoselectivity, for R = Ph and Tol (Scheme 9). 23 In solution, the exo-endo double-[4 + 2] cycloadducts were obtained, and without sensitizer photolysis to carboxylic acids was dominant. These The diphenyl-substituted methylenecyclopropane was found to undergo a photochemical rearrangement to 28.…”

Two pairs of enantiomeric α-pyrone dimers from the endophytic fungus Phoma sp. YN02-P-3

“…7,8 a-Pyrone is a simple heterocyclic dienone system, 9 which is frequently used as the substrate of intramolecular photochemical reactions, in order to investigate the intermolecular cycloaddition reactivity. [10][11][12] During our continuing search for novel bioactive secondary metabolites from endophytic fungi, Phoma sp. was obtained from the sample collected in the plant Sumbaviopsis J. J. Smith from Yunnan Province, China.…”