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

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Skup
Gordon Research Conference on Organic Photochemistry

Mjesto i datum
Andover (NH), Sjedinjene Američke Države, 02.07.1987. - 17.07.1987

Vrsta sudjelovanja
Poster

Vrsta recenzije
Nije recenziran

Ključne riječi
[2+2] and [4+2] photocycloaddition of alkenes and dienes

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 l, l-dimethoxyethylene (DME) gave [2 + 2] cycloadducts 5, 6 and 7, respewctively. The x-ray crystal structures of 4– 7 show that the four- and six-memtered 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 higly twisted triplet excited state, which is the likely precursor of both [4 + 2] and [2 + 2] 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

Napomena
Rad je kao poster prezentiran i na skupu XII IUPAC Symposium on Photochemistry, održanom od 17-22.07.1988.g., Bologna, Italija.

POVEZANOST RADA