Acrylonitrile photocycloadditions

Similar effects were observed in the photocycloaddition of isoprene and a-acetoxyacrylonitrile(55b,56) but not in the cross-addition of the acrylonitrile and cyclopentadiene.[Pg.230]

Acenaphthylene undergoes photocycloaddition to cyclopentadiene(87> and acrylonitrile<68) to yield the following products ... 

A heavy-atom effect on the photocycloaddition of acenaphthylene to acrylonitrile has also been observed.<68) The effect of heavy atoms in this case is seen as an apparent increase in the quantum yield of product formation in heavy-atom solvents as opposed to cyclohexane (the time to achieve about 42% reaction in cyclohexane is greater than that required to produce the same conversion in dibromoethane by a factor of ten). An increase in the rate of acenaphthylene intersystem crossing due to heavy-atom perturbation was proposed to explain this increase in reaction rate. 

Several Ar-alkyl-2-oxo-l,2,3,4-tetrahydroazocine-3-carbonitriles and -carboxylates (88) have been obtained in very low yields by an unusual photocycloaddition of 2-pyridinones and acrylonitrile or methyl acrylate (80T81). The major products are the bicyclo[4.2.0] adducts (89). 

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). 

McCullough and co-workers first reported the photocycloaddition of acrylonitrile (33a) to naphthalene in 1970 [94,95], They systematically investigated the photocycloaddition of 33a to mono- and di-methylnaphthalenes however, the yields and selectivity were not high and usually a complex mixture was produced [128] (Scheme 18). 

Photocycloaddition of phenyl triphenylsilyl thioketones with electron poor olefins (e.g. acrylonitrile) yield thietanes (e.g. 39) in a... 

Photocycloaddition of acrylonitrile in benzene gives a mixture of seven [2+2] cycloadducts, of which the three minor trans-fused components are rapidly isomerized. The major r-fused cyclobuta[ ]thiopyran products arise by head-to-tail addition which places the nitrile group at the 8-position. In the corresponding reaction with 2,3-dimethylbut-2-ene, the trans-iuscd adduct is the major product <2005HCA1922>. 

The formation of trans-products is observed to a lesser extent in the reaction of 3-alkoxycarbonyl-substituted cyclohexenones, in the reaction with electron-deficient alkenes and in the reaction with olefinic reaction partners, such as alkynes and allenes, in which the four-membered ring is highly strained (Scheme 6.11). The ester 26 reacted with cyclopentene upon irradiation in toluene to only two diastereomeric products 27 [36]. The exo-product 27a (cis-anti-cis) prevailed over the endo-product 27b (cis-syn-cis) the formation of trans-products was not observed. The well-known [2 + 2]-photocycloaddition of cyclohexenone (24) to acrylonitrile was recently reinvestigated in connection with a comprehensive study [37]. The product distribution, with the two major products 28a and 28b being isolated in 90% purity, nicely illustrates the preferential formation of HH (head-to-head) cyclobutanes with electron-acceptor substituted olefins. The low simple diastereoselectivity can be interpreted by the fact that the cyano group is relatively small and does not exhibit a significant preference for being positioned in an exo-fashion. 

In the preparative application of [2 + 2]-photocycloadditions of cyclic enones to (substituted) alkenes, two factors concerning product formation are of decisive relevance, namely the regioselectivity and the (overall) rate of conversion. Regarding the regioselectivity in the addition to mono- and 1,1-disubstituted alkenes, Corey had shown that the preferred addition mode of cyclohex-2-enone to isobutene or 1,1-dimethoxyethylene was the one leading to—both cis- and trans-fused—bicyclo[4.2.0]octan-2-ones with the substituents on C(7) [8]. In contrast, in the reaction with acrylonitrile, the alternate orientation was observed to occur preferentially. Similar results were also reported by Cantrell for the photocycloaddition of 3-methyl-cyclohex-2-enone to differently substituted alkenes [14]. No significant differences in the overall rates of product formation for the different alkenes were observed in these studies. In order to explain these observed... 

However, the photocycloaddition of ketones to Z-substituted alkenes does not fit the explanation based on the relative stability of the diradicals. Irradiation of a solution of acrylonitrile 8.22 in acetone 8.21 gives the adduct 8.23, together with dimers of acrylonitrile. This regioselectivity is consistent with a frontier orbital argument. 

The photocycloaddition of acrylonitrile to acenaphthylene is found to be competitive with photodimerization in the non-ionic detergent Nippol PBC-34, while... 

The cycloaddition of acrylonitrile to 4,4-dimethylcyclohexenone yields a mixture of [2 + 2] adducts (38)." These adducts can be chemically converted into the bicyclononane (39). Photocycloaddition of 1,1-diethoxyethylene to the... 

However, the photocycloaddition of ketones to Z-substituted olefins is anomalous if this argument is used but their behaviour is entirely consistent with the frontier orbital argument. Irradiation of acrylonitrile (469) in acetone (468) solution gives the adduct (470), together with dimers of acrylonitrile.378... 

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). 

The photocycloaddition of acrylonitrile to various methyl substituted naphthalenes has been reported. The reactions proceed in poor yield and the products generally result from 1,2-addition to the naphthalene ring. For example, 2-methylnaphthalene gives adduct (72) in 8% yield. This is in contrast to the photochemical reaction of acylnaphthalenes with a-substituted acrylonitriles, which mainly yield products of 1,4-addition of the alkene to the naphthalene... 

The presence of both electron-donor (alkoxy) and electron-acceptor (cyano or carbomethoxy) substituents at the 2- and 3-positions respectively of the pyridine ring, have unlocked its photocycloaddition chemistry, and in recent years several such reactions of these heteroarenes have been described. Previously reported additions of ethenes involved acrylonitrile derivatives, but similar processes are now described with vinyl ethers as the addend. In these systems, however, it seems that the regiochemistry of addition is very sensitive to steric influences. Thus, although the dihydroazocine (48) is formed selectively from the 3-cyano-... 

The 1,2-photocycloaddition of acrylonitrile to naphthols or their methyl or trimethylsilyl ethers produces cyclobutane adducts e,g., 45), and these can be cleaved with base. This provides a synthetic route to (1- or 2-cyanoethyl)-substituted derivatives of the original naphthol. 1-Cyanonaphthalene (46) gives both 1,2-cycloadducts to the ring and a C N cycloadduct on irradiation with 1,2-dimethylcyclopentene, and the two reactions proceed by way of different singlet excited states of the aromatic nitrile. The photophysics of this system has been studied previously, but this is the first report in which the photoproducts are characterized. An intramolecular version of the reaction starting with the substituted 1-cyanonaphthalene (47) gives two 1,2-cycloadducts, the major one... 

Addition of simple ethylenes to polynuclear aromatic compounds has been reported for a variety of systems in recent years.10 The light-induced 1,2-addition of acrylonitrile to naphthalene has been intensively studied by McCullough and co-workers.ei It is, however, now interesting to read that polymerization of the ethylene can occur under such conditions.82 and his group have carried out several studies in this area and they have now described the stereospecific 1,2-photocycloaddition of 1-naphthonitrile with cis- and //wts-l-phenoxypropenes.88... 

Table 10.11. Photocycloaddition of Phenanthrene with Dichloroethylenes and Acrylonitrile ...

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