Cyclohexenone, photochemical addition

Additions to Cyclohexenones and Related Systems - Caldwell and his coworkers have studied the photochemical addition of 1,1-diphenylethene to 4,4-dimethylcyclohex-2-enone. The products from this reaction, carried out in cyclohexane, are shown in Scheme 1. Although other evidence (see reference 9b above and references cited therein) has suggested that an exciplex is not a key interaction in such (2+2)-photocycloaddition reactions Caldwell et al. conclude from their detailed study of this system that a triplet exciplex is involved. Schuster and his coworkers have reported that a variety of cyclic enones (17) -(19) add photochemically to fullerene. The yields of the adducts vary but with some of the less heavily substituted enones the yields can be reasonable as shown by the data under the appropriate structure. Suginome et aO report the synthesis of the cycloadducts (20) by the photochemical addition of various ethenes to the enone (21). The adduct (22) was also synthesized by photochemical addition of methoxycyclohexene to the enone (20). 

Additions to Cyclopentenones and Related Systems. (2 + 2)-Cycloadditions are reported following the irradiation of mixtures of alkyl and aryl 2-thioxo-3/f-benzoxazole-3-carboxylates with alkenes. Cycloaddition also occurs to the CS double bond. The photochemical additions of arylalkenes to 3-phenylcyclo-pentenone and 3-phenyl cyclohexenone have been studied. The regio- and stereochemistry observed in the additions has been rationalized in terms of the stability of the intermediate biradicals. Photocycloaddition of allene to the cyclopentenone derivative (6) in methylene chloride solution at — 78°C affords... 

Additions to Cyclohexenones and Related Systems. Singh and Samanta have described the photochemical addition of substituted cyclohexa-2,4-dienones to cycloheptadiene as a route to 10,10-dimethyltricyclo[7.2.2.0 ]-... 

A full account of the photochemical addition of dienes to cyclohexenone and cyclopentenone has been reported.20-21 The addition process affords [2 + 2]... 

Margaretha and co-workers have described the cycloaddition of some cyclohex-2-enones to acrylonitrile. The addition reactions show moderate regioselectivity and form mixtures of exo- and ewJ6)-5-oxobicyclo[4.2.0]-octane-7-carbonitriles. Madhavan and Pitchumani have reported the dimerization of 2-cyclohexenone confined in clay interlayers (cation-exchanged bentonite). The reaction is remarkably regioselective and affords the head-to-head dimer almost exclusively. The cyclic alkene (24) undergoes photochemical addition to enones to afford the adducts (25) and (26) in the yields shown. 

The photosensitized addition of 1,3-dioxolane and 1,3,5-trioxane to, alkenes was developed a number of years ago as a route to a-alkylated ethers (68JOC805). It has now been shown that 2-methyl-l,3-dioxolane will undergo a photochemically induced conjugate addition reaction to cyclohexenone to afford an adduct (327) in 54% yield which can be hydrolyzed to the diketone (328) (77CJC3986). Functionalized dioxolane (330) was also... 

An additional example is a two-step approach to the preparation of 1,5-cyclo-decadiene. By a photochemical cycloaddition of a substituted cyclobutene and 2-cyclohexenone, a strained tricyclo[4.4.0.02,5]decane system is generated. Thermolysis of the tricycle gave 1,5-cyclodecadiene [52]. 

A review has discussed the photochemical cyclization of a variety of aryl- and heteroaryl-prop-2-enoic acids. Irradiation (A,>340nm) of the cyclohexenone (119) in argon purged benzene solution affords the cyclized derivatives (120) as a 3 1 mixture of diastereoisomers. The formation of the cyclopropyl group arises via the carbene (121) and insertion into a C-H bond of a neighbouring methyl group. This carbene is formed, presumably, from the biradical (122) which arises by addition of the alkene to the excited state of the enone. Further evidence for the carbene intermediate comes from a reaction in methanol when the diastereo-isomeric mixture of the ethers (123) and (124) is obtained." ... 

Additions to Cyclohexenones and Related Systems - Irradiation of 3-methylcyclohexenone in methanol solution in the presence of the ester (42) results in the synthesis of adduct (43) in moderate yields. This product was used as the starting material for an approach to the synthesis of trichodiene. The enone (44) undergoes photochemical reaction with 2,3-dimethylbut-2-ene in benzene or acetonitrile solution and using 350 nm light.The four products were identified as (45), (46), (47) and (48). The formation of the oxetane (45) follows the conventional route and the cycloadduct (48) arises via the biradical... 

Intramolecular Additions to Cyclohexenones and Related Systems. 3-Styrylcyclohex-2-enone undergoes photochemical cyclization to afford 2,3-dihydro-[177]-phenanthrene-4-one. Work carried out on the photostability of curcumin has also examined the photolability of the chalcone (38). This undergoes cyclization to (39) on irradiation. ... 

In the case of monosubstituted cyclobutenone 31, the adduct with lithiovinylsuofone 32 was reported to undergo an extraordinarily facile tandem 47r-67T electrocyclic process (33 34) at - 78 °C to give cyclohexenone 36 [70]. The photochemical process may oblige the opposite direction on a hydroxyl group to be oriented inwardly actually cyanohydrin 37 was reported to give butenolide 39 as a result of an intramolecular addition reaction of (Z)-hydroxyvinylketene 38 [71] (Scheme 6). 

Propellanes containing the bicyclo[4,2,0]octane moiety have been prepared by photochemical [2 + 2] additions. Addition of maleic anhydride or cyclohexenone to A -octalin gives the propellanes (314) and (315). Addition of the enone (316) to cyclohexene gives the propellane (317). ... 

Pioneering progress in the field of [5+1] cycloadditions was made by Sarel et al. [9]. When they treated 1,1-dicyclopro-pylethylene 1 with Fe(CO)s, they obtained unexpectedly cyclohexenone-Fe complex 3, in addition to the desired diene 7t-complex 2 (Scheme 17.1). Cyclohexenone-Fe complex 3 comes from [5+1 ] carbonylation of 1 with CO from Fe (CO)s followed by opening of the second cyclopropane ring. To achieve the [5+1] cycloaddition under mild conditions, they changed the original thermal reaction to a photochemical [5+1] reaction (Scheme 17.2). 

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