Acrylonitrile ortho-photocycloaddition

The carbon-nitrogen triple bond can also undergo ortho photocycloaddition to derivatives of benzene. Al-Jalal et al. [86] found that irradiation of 4-cyanoanisole in acrylonitrile produced three 1 1 adducts. Two of these were formed by the addition of the carbon-carbon double bond of acrylonitrile to positions 1,2 and 3,4, respectively, of 4-cyanoanisole. The third product was an aza-cyclooctatetraene, apparently formed by the addition of the carbon-nitrogen triple bond to the arene, followed by ring opening [87],... 

Ohashi et al. [128] found that the yields of ortho photoaddition of acrylonitrile and methacrylonitrile to benzene and that of acrylonitrile to toluene are considerable increased when zinc(II) chloride is present in the solution. This was ascribed to increased electron affinity of (meth)acrylonitrile by complex formation with ZnCl2 and it confirmed the occurrence of charge transfer during ortho photocycloaddition. This was further explored by investigating solvent effects on ortho additions of acceptor olefins and donor arenes [136,139], Irradiation of anisole and acrylonitrile in acetonitrile at 254 nm yielded a mixture of stereoisomers of l-methoxy-8-cyanobicyclo[4.2.0]octa-2,4-diene as a major product. A similar reaction occurred in ethyl acetate. However, irradiation of a mixture of anisole and acrylonitrile in methanol under similar conditions gave the substitution products 4-methoxy-a-methylbenzeneacetonitrile (49%) and 2-methoxy-a-methylbenzeneacetonitrile (10%) solely (Scheme 43). 

Intermolecular photocycloaddition also occurs between alkenes and simple phenols. The swing from meta addition illustrated above in the [3 + 2]-mode to ortho-addition is a result of charge-transfer interactions between the alkene and the phenol and a greater charge transfer favours the ortto-addition mode. These aspects have been the subjects of reviews . This reaction mode is exemplified by the addition of acrylonitrile... 

Azocine formation by photocycloaddition of acrylonitrile to arenas is also observed when cyanobenzenes and cyanonaphthalenes are irradiated with ultra-violet light in the presence of phenols. The products have the structure (70) and are presumed to be formed by thermal ring opening of the primary ortho adducts (71). 

---