Naslov
Stereochemistry and mechanism of the [2 + 2] and [4 + 2] photocycloaddition of alkenes and dienes to pummerer's ketone

Autori
Mintas, Mladen ; Schuster, David I. ; Williard, Paul G.

Izvornik
Tetrahedron (0040-4020) 44 (1988), 19; 6001-6012

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
Pummerer's ketone ; photocycloaddition of alkenes and dienes ; stereochemistry and mechanism ; nanosecond flash photolysis

Sažetak
Irradiation of Pummerer's ketone (PK) in furan gave the trans-fused [4+2] cycloadducts 2 and 3, whose structures were determined by their 1H NMR spectra and confirmed by X-ray crystallography. Irradiation of PK in the presence of tetramethylethylene (TME) gave cycloadduct 4 and with 1, 1- dimethoxyethylene (DME) gave [2+2] cycloadducts 5, 6 and 7, respectively. The X-ray crystal structures of 4-7 show that the four- and six-membered rings of 4 and 7 are trans-fused, and 5 and 6 are cis-fused, respectively. Differential quenching of the formation of cycloadducts 2-5 and 7 by the free radical TEMPO was observed. Formation of cycloadducts 2-4 was also quenched differentially by O2. A short lived (15 nsec) transient observed on nanosecond flash photolysis of PK is suggested to be a highly twisted triplet excited adducts. It is proposed that stepwise addition of furan and alkenes to PK triplets gives triplet biradicals, which can be intercepted by TEMPO and O2, and that these reactions probably do not involve a ground state trans-cyclohexenone intermediate.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

POVEZANOST RADA