Hexenes photolysis

The reaction of EtsSiH with [l.l.l]propellane under photolytical decomposition of di-tert-butyl peroxide afforded products 17 and 18 in 1 3 ratio (Reaction 5.15) [36]. A rate constant of 6.0 x 10 M s at 19 °C for the addition EtsSi radical to [l.l.l]propellane was determined by laser flash photolysis [37]. Thus, it would appear that [l.l.l]propellane is slightly more reactive toward attack by EtsSi radicals than is styrene, and significantly more reactive than 1-hexene (cf. Table 5.1). 

Photolysis of octafluorohexa-1.3,5-triene in the gas phase gives bicyclic hexene 24 as the major product (53 % yield) along with perfluoro(3-vinylcyclobutene) (30 % yield).19 Bicyclic product 24 is presumed to be formed via cyclohexadiene 23. Mercury-vapor sensitization accelerates the reaction and leads to a higher percentage of bicyclic product. Photolysis of octafluorohexa-1,3,5-triene in solution gives only EjZ isomerization. Heating octafluorohexa-1,3,5-triene at 400 to 500 C provides perfluorocyclohexa-1,3-diene (23) as the sole product in 60 to 80% conversion.19... 

It is essential to note that the mechanism which involves diradical intermediates is based purely on analogy and as such remains to be proved. If tetramethylene diradicals are formed, it is surprising that, unlike monoradicals, they do not recombine with each other or abstract hydrogen atoms from other molecules. It has been claimed that photolysis of cyclopentanone in the presence of ethylene leads to cyclohexane and hexenes as products presumably through the reactions 5 and 6 (17). 

Photolysis of cyclohexanone gives rise to carbon monoxide, ethylene, propylene (1), cyclopentane, 1-pentene (3), and 5-hexenal (29). Cyclo-hexenyl cyclohexanone, water, and a polymer have also been reported as products, especially when the photolysis is conducted in the temperature range from 100°-300° in the presence of short wavelength radiation (3). At 3130 A. and over the temperature range of 100°-300° the ketone that is decomposed is almost fully accounted for in the products (5) and the stoichiometry of the products fits the eq. 15-18 (3,27) ... 

The products of the photolysis of cycloheptanone are carbon monoxide, propylene, a hydrocarbon fraction of the molecular formula C Hu (l),and 6-heptenal (31). The hydrocarbon fraction consists of 1-hexene and cyclohexane in the ratio of 1 4.7. A trace of ethylene has also been observed among the products. From a consideration of mass balance, the following reactions may represent the stoichiometry of the photolysis. 

The photolysis of cyclohexanone has been studied by several workers. The formation of 5-hexenal, presumably by an intramolecular rearrangement as in the vapor phase by eq. 18, has been observed in the pure liquid (36) and in 1-octene solution (21). 

Photolysis of various diazabicyclo[3.1.0]hexenes related to (300) leads to mixtures of dienes and bicyclo[1.1.0]butanes, eg. ... 

Rates of reaction of CO with (arene)Mo(CO)2 (alkane) and M(C0)5 (alkane), where M = Cr, Mo, W, have demonstrated that the reaction with Cr(CO)5 (alkane) involves an interchange mechanism while for Mo and W the mechanism is more associative. These resnlts are consistent with the known ability of the higher homologs to expand beyond a coordination number of 6. Flash photolysis and ultra high speed detection (0.4 ps, 4cm resolution) have allowed direct observation (Figure 6) of the vibrational cooling of CpCo(CO)(n-hexane), CpCo(CO)(n-hexene), and the group VI carbonyls. ... 

Photolysis of cyclotrisilane 72 in the presence of l,6-bis(trimethylsilyl)-(Z)-3-hexene-l,5-diyne resulted in the formation of yellow crystals of bis(silirene) 101 with an olefinic double bond linkage in 76% yield (Equation 26) <20020M636>. 

The photolysis of higher olefins has not received a lot of attention. The reader is referred to the original literature for the following compounds m-pentene-2, Borrell and Cashmore cw-hexene, Chesick . ... 

The products of the photolysis of cyclohexanone are CO, C2H4, C3H6, cyclo-C5H10, as well as 5-hexenal . Cyclohexenyl cyclo-... 

The reactions taking place in the vapour phase also occur in the condensed phase, and their mechanisms are probably similar. However, as may be expected on the basis of the results obtained for the gas phase photolysis, the formation of olefins, cycloparaffins, and CO is of less importance, while that of the saturated aldehydes is more important in the liquid phase or solution, where energy dissipation by collision is more efficient. The decarbonylation products were shown to be only of minor importance in the photolysis of liquid cyclopentanone and cyclohexanone . The unsaturated aldehyde was found to be the main product in the liquid-phase photolysis of cyclopentanone (methyl cyclohexanone . Unsaturated aldehydes were also identified in the photolysis products of other cyclic ketones in the liquid phase as well as in solution . ... 

An additional and noteworthy feature of the 3-allylcyclopropene photochemistry is side chain cleavage-recombination with retention of the three-membered ring. The photolysis of 246b delivers, in addition to the bicyclo[3.1.0]hexene 248b, the rearranged cyclopropenes 249 and 250. Homolytic cleavage of the cyclopropenyl-allyl bond and subsequent radical recombination at a phenyl-substituted centre accounts for these observations (equation 80). 

Proof for the triplet character of the hydrogen abstracting species is obtained in sensitization experiments. Thus, direct photolysis of ethyl azidoformate in cyclohexene results in the formation of only 3% of the hydrogen abstraction product (urethane) and a trace of 6w-cyclo-hexene -. In the sensitized photoreaction, where triplet nitrene is produced directly, the urethane yield increases to 74%, the yield of Aw-cyclohexene to 63%. 

Photolysis of the cyclic vinyl ketone 5,5-dimethyl-3-azido-2-cyclo-hexene-l-one (61) in aqueous tetrahydrofuran resulted in ring enlargement to the azepine (62). Irradiation of the same azide in benzene did not however lead to photodecomposition. A reaction path involving a cyclic ketene-imine was put forward. 

Under the same conditions, photolysis in benzene of 9,10-deoxytridachione (6), isolated from Tridachiella diomedea, " a marine mollusc, using a 450-W Hanovia lamp for three hours gave a simple photoproduct 7 (R = H) in 85% yield having the bicyclo[3.1.0]hexene ring system of crispatene (R = COEt) found in Tridachia crispata, another mollusc from the Caribbean. 

As mentioned earlier, direct irradiation of 1,2-dihydronaphthalenes leads to a variety of photoisomerization reactions which can be attributed to the initial formation of the )-vinyl-orf/ o-quinodimethane isomer by electrocyclic ring opening. For example, irradiation of the parent compound 115 with an intense, broad-band light source yields the isomeric benzobicyclo[3.1.0]hexene derivative (158) as the main photoproduct, via secondary photolysis of the initially-produced cu-vinyl-orf/zo-quinodimethane isomer 116 (equation Such compounds are short-lived due to rapid thermal ring closure to... 

Photolysis rates and subsequent product branching ratios of unsaturated -dicarbonyls (an important source of radicals) have been adjusted according to Thuener et al. (2003) for butenedial and 4-oxo-2-pentenal, and Graedler and Barnes (1997) for 3-hexene-2,5-dione. The photolysis rates of the epoxydicarbonylene products have also been increased as they were originally estimated by analogy with the unsaturated -dicarbonyls. 

While many examples are available demonstrating the mechanism-based stereoselectivity in carbene transfer reactions, knowledge of the simple diastereoselectivity exhibited by alkylcarbenoids is rather limited. A few typical reactions (Table 1) arc sufficient to demonstrate the basic principles (for further examples, see Vol. E 19h, pp 165-390). Thus, photolysis of diiodomethane in the presence of (E)- or (Z)-3-hexene stereospecifically provides /r ns-l,2-diethylcyclopropane and cM-l,2-diethylcyclopropane, respectively1. For a general procedure for this photocyclopropa-nation method, which proceeds via the iodomethyl cation, see Vol. E 19b, p 190. 

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