Photochemical nucleophile-olefin combination, aromatic substitution (photo-NOCAS) reaction. Part 9: methanol-2,6-dimethyl-1,6-heptadiene, and 1,4-dicyanobenzene

• Published in: Canadian journal of chemistry Vol. 73; no. 6; pp. 762 - 771
• Main Authors: Connor, Dennis A, Arnold, Donald R, Bakshi, Pradip K, Cameron, T. Stanley
• Format: Journal Article
• Language: English
• Published: Ottawa, Canada NRC Research Press 01.06.1995
• ISSN: 0008-4042; 1480-3291
• DOI: 10.1139/v95-096

The photochemical nucleophile-olefin combination, aromatic substitution (photo-NOCAS) reaction of methanol, 2,6-dimethyl-1,6-heptadiene, and 1,4-dicyanobenzene yields three distinct types of 1:1:1 adducts: an acyclic product, 4-(1-methoxymethyl-1,5-dimethyl-5-hexenyl)benzonitrile ( 8 , 5%); a cis-trans pair of cyclohexanes, 4-(3-methoxymethyl-1,3-dimethylcyclohexyl)benzonitrile ( 9 cis (12%) and 9 trans (11%)); and a cis-trans pair of cycloheptanes, 4-(4-methoxy-1,4-dimethylcycloheptyl)benzonitrile ( 10 cis (12%) and 10 trans (10%)). Variation in the concentration of the nucleophile, methanol, and codonor, biphenyl, affects the product ratio and it has been possible to establish the mechanisms for the formation of these products. The acyclic product is formed by a typical photo-NOCAS reaction, that is, addition (anti-Markovnikov) across one of the heptadiene double bonds. The cyclohexane products are formed following 1,6-endo cyclization of the intermediate β-alkoxy radical. And the cycloheptane products result from 1,7-endo,endo cyclization of the initially formed 2,6-dimethyl-1,6-heptadiene radical cation. Comparison of the relative rates of these cyclization processes can be made with those of the next smaller homolog, 2,5-dimethyl-1,5-hexadiene. Keywords: photochemistry, photoinduced electron transfer, radical ions, radicals, cyclization.