The photochemistry of 1-cyano-2,3-benzobicyclo[4.2.0]octa-2,4,7-triene

Abstract

The title compound (10) wasprepared, along with the4-cyano isomer (11), by the direct irradiation of 5-cyanobenzocyclooctatetraene (9); the yields were 82% (Dlo = 0.0030) and 12% (@,, = 0.0004) respectively. Triene 10 was thermally and photochemically reactive. Heating solutions of 10 at 150°C for 1 h gave COT 9 quantitatively. On direct irradiation 10 forms 5-cyanobenzosernibullvalene (12; 5%, @ = 0.019), COT 9 (70%, @ = 0.56), and 1-cyanonaphthalene (14%, @ = 0.078). Sensitized irradiation of 10 gave 9 exclusively (92%, @ = 0.88). COT 9 was also produced by the direct irradiation of semibullvalene 12 (75%, @ = 0.13). Studies with deuterium labelled 10 suggest that the photoformation of COT 9 involves a simple electrocyclic opening of the cyclobutene ring of the triene. Additionally, the labelling results indicate that the formation of semibullvalene 12 from 10 derives from the operation of two reaction pathways, the major one of which appears to be a Zimmerman di-T-methane rearrangement. The mechanism proposed for the minor pathway to 12 has not been observed in other bicyclo A 150"C, des solutions de 10 se transforment en 9 en rendements quantitatifs. Par irradiation directe, 10 conduit au cyano-5 benzo semi-bullvaltne (12; 5%, @ = 0.019), a 9 (70%, @ = 0.56) et au cyano-1 naphtalkne (l4%, @ = 0.078). Par irradiation sensibiliste, 10 conduit a 9 uniquement (92%, @ = 0.88). Le compose 9 se forme aussi de la photolyse directe du semi-bullvaltne 12 (75%, @ = 0.13). Des ttudes de marquages au deuterium suggkrent que 9 se produit photochirniquement du tritne par un mtcanisme qui comporte l'ouverture electrocyclique de l'anneau du cyclobuttne de 10. De plus, des etudes de marquages dtmontrent qu'il y a deux mecanismes qui entrent en jeux dans la transformation 10-12. Le mkcanisme majeur derive d'une transposition di-T-mithane de Zimmerman. Un nouveau mtcanisme est propos6 pour la voie mineure qui fournit 12.

5.06 Di-π-methane, Oxa-di-π-methane, and Aza-di-π-methane Photoisomerization

“…The complex reaction mechanisms of the photochemical transformations of such cyano substituted tricyclic compounds have been systematically investigated. 67,68 Similar studies have also been performed with the unsubstituted core structure and a methyl derivative. 69 A photochemical rearrangement observed with C 60 fullerene derivatives has been explained by a di-p-methane photoisomerization.…”

Relationships between the aqueous acidities of some carbon, oxygen, and nitrogen acids and the calculated surface local ionization energies of their conjugate bases

“…The calculation of solution acidities is even more demanding since quantum chemical approaches must be supplemented by statistical mechanical considerations. 2 We have recently shown, for a series of azines and azoles, that an excellent correlation exists between the lowest values of the average local ionization energies 7(r), computed on their gas-phase three-dimensional molecular surfaces, and the aqueous solution acidities (p7ft's) of their conjugate acids.3 45In this study, we explore possible extensions of this relationship to other classes of acids. We show that there exist linear relationships between our calculated 7(r) values and the experimentally determined pKa's of the conjugate bases of a variety of carbon, nitrogen, and oxygen acids.…”

(5Z,7Z,9Z)-5,10-Dibromobenzo[8]annulene

“…For general background to photochemical conversions of benzocyclooctatetraenes, see: Bender et al (1982Bender et al ( , 1986Bender et al ( , 1988Bender et al ( , 1991. For details of the synthesis, see: Barton et al (1964).…”

“…The title compound was prepared as a starting material for synthesis of the corresponding dinitrile derivative, which was of interest in connection with studies of the photochemical conversions of benzocyclooctatetraenes (Bender et al, 1982;1986;1988;1991). In view of the paucity of structures that are crystallographically established for mono-benzofused cyclo-octatetraenes, we decided to undertake a crystallographic study of (I).…”