Cyclopropane photolysis

C3H0 + CjD suggests its formation by a molecular elimination and this is the most important primary process in cyclopropane photolysis. 

B.iv. Photolysis of Cyclopropanes. Photolysis of cyclopropanes generates carbenes via elimination of an alkene.254 photolysis of 1,1-dimethylcyclopropane in the gas phase, for example, gave dimethylmethyl-ene (Me2C ) and ethene. s Similarly, irradiation of 9,10-dihydro-9,10-methanophenanthrene (318) gave carbene and phenanthrene.256 Oxiranes can be photolyzed to carbenes as well.257... 

Bicyclo[4.1.1] or [3.2.1]octenones and cyclopropanes have resulted from decomplexation of the iron tricarbonyl group from the alkyl-allyliron tricarbonyl complex, using oxidative (i.e., GO atmosphere) or carbonylative methods for the bicyclooctenones and ceric ammonium nitrate (GAN) for the cyclopropanes. Photolysis of analogous tricarbonyl iron complexes leads to monoolefmic hydrocarbons or aldehydes. The kinetics of GO substitution in reactions of 77 -cyclopropenyl complexes of iron is also reported. " A number of comprehensive reviews have appeared since 1992, illustrating the chemistry of ry -allyliron complexes. 

Ring contraction to cyclopropanes (413) with the formation of azo side-chains is observed in the photolysis of 5-phenylpyrazolines (71BSF1925) and to azetidinones (414) in the photolysis of 5-pyrazolidones (69JCS(C)2624, 83JCS(P2)llll). 

Photolysis of the parent compound (44) yields singlet methylene, as evidenced by its stereospecific addition to ( )-butene. The cyclopropane is formed together with the characteristic insertion products of methylene (62MI50800, 64PAC(9)527)... 

Cyclopropanations by carbenes from chlorodiazirines were observed in several cases, e.g. with the r-butyl compound. Cyclopropanation and stabilization by ring enlargement and by elimination compete in chlorocyclobutyldiazirine photolysis. 

The photolysis of a-diazosulfones dissolved in alkenes provides sulfonyl-substituted cyclopropanes in high yields. This is exemplified by the preparation of l-(p-methoxyphenylsulfonyl)-2,2,3,3-tetra-methylcyclopropane in 75% yield from -methoxybenzenesulfonyl-diazomethane and 2,3-dimethyl-2-butene. A similar addition to [Pg.101]

Thermolysis of (24) gives 4-methylcholest-4-ene-3,6-dione (25) as the sole product,whereas photolysis provides the 4,5-cyclopropane (26) in addition to (25).2°2... 

There has been new information on the products of photolysis of derivatives of compound 1. Low temperature irradiation of the ester 254 gives a ketene (93JACS8621) the isolation of an isomeric ketene from a 3-pyridyldiazo ester suggests the involvement of the open chain form 255. Photolysis of the 3-phenyl derivative 256 in the presence of cyclopentadiene gives exo and endo cyclopropanes and a dipyridylstilhene, suggesting the intermediacy of the carhene 257 (99JOC6635). 

The methylethylcarbene which is formed thermally from methyl-ethyldiazirine at 160°C gives the same products as that from butanone p-toluenesulfonylhydrazone and bases in aprotic solvents." However, photolysis of the same diazirine gives a different mixture of C4H8 hydrocarbons. Considerable amounts of 1-butene are formed, the trans-butene content is reduced by half, and the amount of methyl cyclopropane increased fivefold. ... 

Photolysis of the sulphinyl-3H-pyrazole 587 in ether or methylene chloride leads to the formation of a relatively stable carbene 588 that can be identified by physical methods. When the irradiation is performed in ethyl vinyl ether or in furan, the expected cyclopropanes are formed smoothly and stereospecifically683 (equation 374). 

One of the earliest reported thermal reactions of Fischer carbene complexes was the reaction with olefins to give cyclopropanes [127]. More recently it has been shown that photolysis accelerates inter molecular cydopropanation of electron-poor alkenes [128]. Photolysis of Group 6 imine carbenes with alkenes... 

Pyrazolines (51) can be converted to cyclopropane and N2 on photolysis""" or pyroiysis. The tautomeric 2-pyrazolines (52), which are more stable than 51 also give the reaction, but in this case an acidic or basic catalyst is required, the function of which is to convert 52 to 51." In the absence of such catalysts, 52 do not react/ In a similar manner, triazolines (53) are converted to aziridines." Side reactions are frequent with both 51 and 53, and some substrates do not give the reaction at all. However, the reaction has proved synthetically useful in many cases. In general, photolysis gives better yields and fewer side reactions than pyrolysis with both 51 and 53. S/Z-Pyrazoles" " (54) are stable to heat, but in some cases can be converted to... 

Tl(III) < Pb(IV), and this conclusion has been confirmed recently with reference to the oxythallation of olefins 124) and the cleavage of cyclopropanes 127). It is also predictable that oxidations of unsaturated systems by Tl(III) will exhibit characteristics commonly associated with analogous oxidations by Hg(II) and Pb(IV). There is, however, one important difference between Pb(IV) and Tl(III) redox reactions, namely that in the latter case reduction of the metal ion is believed to proceed only by a direct two-electron transfer mechanism (70). Thallium(II) has been detected by y-irradiation 10), pulse radiolysis 17, 107), and flash photolysis 144a) studies, butis completely unstable with respect to Tl(III) and T1(I) the rate constant for the process 2T1(II) Tl(III) + T1(I), 2.3 x 10 liter mole sec , is in fact close to diffusion control of the reaction 17). 

Cyclopropylchlorocarbene [20] has been generated by UV photolysis (A = 335 nm) of cyclopropylchlorodiazirine [21] frozen in a nitrogen matrix at 12 K (Ho et al., 1989). IR and UV spectra of [20] have been recorded. The reaction of [20] with HCl resulted in the formation of (dichloromethyl)-cyclopropane [22], and annealing of the matrix gave (dicyclopropyl)dichloro-ethene [23]. Subsequent irradiation (A = 450 nm) of the carbene [20] led to its isomerization to 1-chlorocyclobutene [24], which was partialy destroyed to give ethene and chloroacetylene. Ab initio calculations predict the existence of two carbene conformers, but attempts to distinguish them in IR or UV spectra were unsuccessful. 

A. N. Tarnovsky, V. Sundstrom, E. Akesson, and T. Pascher, Photochemistry of diiodomethane in solution studied by femtosecond and nanosecond laser photolysis. Formation and dark reactions of the CH2I-I isomer photoproduct and its role in cyclopropanation of olefins. J. Phys. Chem. A 108(2), 237-249 (2004). 

D. L. Phillips, W.H. Fang, and X. Zheng, Isodiiodomethane is the methylene transfer agent in cyclopropanation reactions with olefins using ultraviolet photolysis of diiodomethane in solutions a density functional theory investigation of the reactions of isodiiodomethane, iodomethyl radical, and iodomethyl cation with ethylene. J. Am. Chem. Soc. 123(18), 4197-4203 (2001). 

The nature of the photochemically produced methylene has been the subject of considerable study. Evidence tends to indicate that this species is produced in its singlet state photochemically. Photolysis of diazomethane in the gas phase or in solution in the presence of excess cis- or trans-2-butene produces cyclopropane products due to methylene insertion in which the... 

Photolysis of phenyldiazomethane in cis- or trans-butene leads to nearly stereospecific cyclopropane formation, although some C—H insertion occurs<2W ... 

The yield of trans product (18) is decreased by the presence of a radical scavenger such as 1,1-diphenylethylene and increased by dilution of the reactants with methylene chloride or butane, indicating this product to result from the triplet carbene. A heavy-atom effect on the carbene intermediate was observed by photolysis of a-methylmercuridiazoacetonitrile. With c/s-2-butene as the trapping agent either direct photolysis or triplet benzophenone-sensitized decomposition results in formation of cyclopropanes (19) and (20) in a 1 1 ratio ... 

The yields of cyclopropanes in this case are low in relation to the amount of acetophenone formed. However, similar cyclopropane product ratios are obtained when photolysis is carried out in the presence of Michler s ketone as sensitizer. Thus the carbene intermediate produced in the direct irradiation is thought to be a triplet, as suggested by the nonstereospecificity of its addition. Whether this intermediate arose from singlet diazoacetophenone (via singlet decomposition and intersystem crossing of the singlet carbene) or by decomposition of the triplet molecule was not determined. 

The photochemistry of l,l,5,5-tetraphenyl-3,3-dimethyl-l,4 pentadiene (1) has been studied in detail by Zimmerman and Mariano.<7) Photolysis of compound (1) gave 1,1-diphenyl-2,2-dimethyl-3-(2,2-diphenylvinyl) cyclopropane ... 

An interesting gas-phase study of the photolysis of ftmy-l-phenyl-2-butene has been published by Comtet.(39,40) He has found that (a) it was not possible to quench the formation of the cyclopropane product under conditions that reduced the fluorescence quantum yield, (b) sensitization by acetophenone only gave cis-trans isomerization, and (c) the quantum yield of cyclopropane formation in the direct photolysis decreases as n-butane is added to the reaction mixture. Comtet suggests that the data are consistent with a reaction from the second triplet state. 

While direct photolysis of (46) gave (48), the sensitized photolysis of (46) with acetophenone gave only the cyclopropane product (>93%). These authors favor a stepwise oxa-di-w-methane reaction mechanism (8.69) inasmuch as a concerted reaction should produce the product without a change in multiplicity. That is, the product would have to be formed in the triplet state and not enough energy is available for the product to be formed in an excited state ... 

Diazobutane yields 1-butene, cis- and mz/w-2-butene, and methyl-cyclopropane on gas-phase photolysis. Product distributions are independent of pressure (50-200 mm Hg) and the presence of nitrogen up to 2 atm(24) ... 

Photolysis of diazocyclopentadiene in trans- and cw-methyl-2-pentene results in products (12) and (13), respectively, in an essentially stereospecific manner (1-2% of the t/ww-cyclopropane was observed to result from addition to the cis olefin)<26> ... 

EPR studies of diphenylmethylene and a number of other arylmethylenes have indicated that these carbenes have triplet ground states.<30) Photolysis of diphenyldiazomethane in olefin matrices results in the formation of triplet diphenylmethylene, which undergoes primarily abstraction reactions with the olefins. Cyclopropanes are produced as minor products. 

Photolysis of this azoketone in olefinic solutions yields no cyclopropane product. However, a recent report by Skell and Velenty<36) indicates that methylmercuridiazoacetone produces high yields of cyclopropanes upon photolysis in olefinic solution ... 

The compound 251 decarbonylates on photolysis to bis(4-hydroxyaryl) acetylene 253, which is easily oxidized to the quinonoid cumulene 254. This is also obtained by thermal decarbonylation of the product of oxidation of cyclopropenone 251, the diquinocyclopropanone 252. Likewise, the blue derivative of 3-radialene 256 (a phenylogue of triketo cyclopropane) is formed from tris-(4-hydroxyaryl) cyclopropenium cation 255 by oxidation34. ... 

The Y-intercept ( 3 /k Eq. 13) of the reciprocal correlation for the photolysis of diazirine 21-C1 in TME was 2.18, which translated into a 68% incursion of diazirine excited state in the genesis of the rearrangement products, 22-C1 and 23-C1 carbene 17-C1 only accounted for 32% of these products.28 A similar conclusion followed from the ratio of rearr/addn (68 32) at a high concentration (6.7 M) of TME in pentane, where carbene 17-C1 was almost completely diverted to the cyclopropane, and 22 and 23 were exclusively derived from the excited diazirine.28... 

In addition, 18-19% of isobutene and chloroacetylene formed via fragmentation. Photolysis of the diazirine in up to 9 M trimethylethylene in pentane led to a sharp decrease in 27 and 28 (to 32% and 8.5%), along with 40% of cyclopropanes formed via the capture of 19. However, the yield of isobutene and chloroacetylene was unchanged, indicating that these products did not stem from the carbene, but arose directly by fragmentation of its excited diazirine precursor.45... 

Cyclopropanated phenanthrenes revert to phenanthrene and carbenes on photolysis CH2,49 CC12,50 CBr2,51 CBrCl,51 and f-BuCH15d have been generated this way. Platz et al.25 used 37 (R=PhCH2) to generate benzylchlorocarbene (10a) for comparison with 10a generated from diazirine 9a cf. Scheme 2. 

Repetition25 of the 9a photolysis in the presence of TME in either isooctane or CH2C12 confirmed that correlations of addn/rearr vs. [TME] were indeed curved, as previously observed.17,19,33 However, generation of PhCH2CCl from 37 by photolysis at 308 nm gave linear correlations of addn/rearr vs. [TME].25 Thus, curvature in the addn/rearr correlations is precursor dependent, and is not due to the intervention of a CAC. If such a complex does form, it must continue on to cyclopropane faster than it reverts or rearranges to fl-chlorostyrene by... 

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