The photolyses of 5,6,7,12,13,14-hexahydro-6,13-methanodibenzo[A,F]cyclodecen-l5-ones 1 , 2 and 3 have been investigated. After Norrish type 1 cleavage, diester 1 gave the alkenes E-5 and 2-5 via loss of carbon monoxide and hydrogen transfer, while 2 and 3 gave ketenes 10a and l o b , respectively, by transannular migration of an a-hydrogen, which was quenched with MeOH, giving the monoester 6 and diesters cis-11 and trans-11, respectively. Photolysis of deuteriated 2 and 3 revealed that the hydrogen transfer is an intramolecular process and the Norrish type 1 cleavage is the rate-determining step (K,/K, = 1.09 & 0.05). Naphthalene was effective in quenching the photolysis of 1 , 2 and 3 at -70 "C, but quenching was incomplete at 5 "C. It was postulated that the two annulated benzene rings might circumscribe the carbonyl group by stereodynamic inversion and that the naphthalene molecule could not come close enough for the energy transfer.Previously, it was reported 2*3 that 3,6-methanodibenzo[aflcyclodecen-15-one and the dinaphtho-and benzonaphthoderivatives exist in a stereodynamic equilibrium between the two chair-boat forms at room temperature. From the measured AG value (10-15 kcal mol-'), it was suggested that the inversion between C-B and B-C is a stepwise process occurring via an intermediate twin-chair conformer, T-C (Scheme 1).

No abstract

No abstract

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.