Miscellaneous Reactions Involving Three-membered Ring Compounds

2 Miscellaneous Reactions Involving Three-membered Ring Compounds - 

Armesto and co-workers have reported the photochemical behaviour of the vinylcyclopropane derivatives (98) under w-methoxyacetophenone sensitisation in methylene chloride as the solvent. A variety of products are formed, the nature of which is dependent upon the substituent on the cyclopropyl ring. The key intermediate is believed to be the biradical (99) that is formed following energy transfer. A study of the effect of wavelength on the outcome of the irradiation of (100) has been reported. At short wavelengths (250 and 254 nm), it is thought that the S2 state of (100) is populated and this results in the formation of the three products (101), (102) and (103) in a ratio of 6 1 1. 

A report by Radzig et alP has given details of the control exercised by silica surfaces on the photochemical conversion of the allyl radicals (104) into the isomeric cyclopropyl radicals. Free radicals are involved in the photoreaction of phenylcyclopropane with trifluoromethylsulfenyl chloride and many products are obtained.  

Cyclopropyl cyanide is photoreactive on irradiation at 193 nm. This treatment brings about elimination of a cyano radical with the fission of the cyclopropane 

A vibrationally excited biradical is a key intermediate in the photochemical ring opening of 3-methyl-2-(l-naphthyl)2//-azirine to afford a ketene imine. Calculations have been carried out in a study of the mechanism of ring opening of 2//-azirines.  

Asymmetric induction within 1,2-diphenylcyclopropane on photolysis in P-cyclodextrin has been studied.Recent research has shown that cis-2,3-diphenylcyclopropane-1-carboxylic acid does not undergo ISC on direct irradiation. The reaction encountered is isomerization to the corresponding trans isomer via a 1,3-biradical intermediate. Exothermic bond cleavage is the dominant reaction within radical cations of cyclopropylamines formed by SET to DCA. The photoheterolysis of 9-cyclopropyl-9-fluorenol has been studied in non-acidic zeolites. The rate of formation of the resultant cation is dependent upon the alkali metal counterion. 

A detailed spectroscopic and calorimetric study of the photorearrangements of (93) has shown that both zwitterionic and biradical species are involved in the isomerization.DCA-sensitized irradiation of the bicyclopropenyl compounds (94) results in conversion into Dewar benzene derivatives (95) and (96) and eventually into the corresponding benzene derivatives (97). The irradiation 

The two-bond photochemical cleavage product, 1,5-hexadiene, obtained from bicyclo[3.1.0]hexane arises from the first excited singlet state of the starting material. This proposal has been substantiated by calculations at the CASSCF level.Both cis- and /raw -9-diphenylvinylidene-bicyclo[6.1.0]nonanes undergo isomerization on irradiation in the presence of Michler s ketone. 

2 Miscellaneous Reactions Involving Three-membered Ring Compounds -Pincock et al have observed the photochemical conversion of the cyclopropane derivative (60) into the cyclobutane (61, 75%). This reaction is proposed as an example of a cyclopropyl-Jt-methane process involving an aryl 

The direct irradiation at 254 nm of the aUenes (67) in hexane gives the molecule in its triplet state. Bridging within this state affords the intermediate biradical (68). Bond formation then yields the major products (69) and (70). Minor products (71) and (72) are also formed. Irradiation at k 280 nm fails to yield products. However, acetophenone sensitization is effective. The authors suggest that in this instance the vinyl moiety is the chromophore which is excited and that intramolecular energy transfer is involved. The yields obtained from the reactions are shown in Table 1. 

A two-photon process has been identified following the flash photolysis of 1,3-dichloro-l,3-diphenylpropane. The 1,3-biradical (73) yields 1,2-diphenylcyclo-propane. 

The cyclopropane derivative (85) undergoes photochemical reduction when 

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