2- cyclobutanones, photolysis

Solvent Dependence of Product Formation from Cyclobutanone Photolysis (313 nm Excitation)... 

Figure IX-E-6. Plot of the quantum yields of the primary processes in cyclobutanone photolysis as a function of wavelength data from McGee (1968) figure from Calvert et al. (2008).

Photochemical transformations of conjugated cyclohexenones, 317 Photochemical transformations of non-conjugatea ketones, 292 Photochemistry of cyclobutanones, 293 Photolysis of nitrites, 253... 

As stated previously, the photolysis of cyclobutanone in ethanol solution results in an 8% yield of an acetal, presumably formed from ethanol addition to a carbene intermediate. Alkylation of the a positions of cyclobutanone increases the yield of this rearrangement product,(22)... 

In ethanol solution 1,2-benzocyclobutenedione undergoes reaction to produce a lactol ether, the analog of the products produced upon photolysis of the tricyclic ketones and cyclobutanones discussed above,<30)... 

Photolysis of pentacarbonylcarbenechromium complexes produce species that react as if they were ketenes. although no evidence for the generation of free ketenes has been observed. Indeed, photolysis of chromium (alkoxy) carbenes in the presence of a range of simple alkenes produced cyclobutanones 1 in good to very good yield.8,9... 

Similarly, photolysis of chromium complex (CO)5Cr=C(OMe)(c-Pr) in the presence of two equivalents of the optically active 3-ethenyl-6(S)-phenyl-2-oxazolidinone under 90 psi CO pressure produced in high regio- and diastereo-selectively the 3-oxazolidine-substitued (2i ,3S)-cyclobutanone, in optical purity of > 97% de (equation 75)148. 

Exercise 28-10 Write a mechanism for formation of cyclobutane from the photolysis of cyclopentanone, and ketene from the photolysis of cyclobutanone. 

Photolysis of cyclobutanone leads to the formation of ethylene, ketene, carbon monoxide, propylene (3), and cyclopropane (5). The formation of an isomeric product, presumed to be 3-butenal, in small yield has been reported (31). The yields of ethylene and ketene have been found to be approximately equivalent (6). The yield of carbon monoxide is in excess of the yield of hydrocarbons (5,6). The discrepancy has been attributed to the formation of a polymer (5) although no direct evidence to substantiate this explanation has been obtained. The stoichiometry of the decomposition may be represented by the following equations ... 

The photolysis of cyclobutanone in the presence of 20- to 50-fold excess of ethylene has been reported (17). In this instance various five-carbon olefins but not cyclopentane are said to be observed among the products. The hydrocarbons are believed to be formed by a reaction between a tri-... 

Hegedus, L.S., Bates, R.W., and Soderberg, B.C. (1991) Synthesis of optically active cyclobutanones by photolysis of chromium-alkoxycarbene complexes in the presence of optically active ene-carbamates. Journal of the American Chemical Society, 113, 923—927. 

Similar to the thermal reaction of ketenes with alkenes, the photolysis of alkoxycarbenes 18 in the presence of (electron-rich) olefins 19 leads to cyclobutanones (Scheme 6) [9]. In these reactions the sterically more strained [2 + 2] cycloadducts of type rac-17 are generally formed with good regio- and diastereoselectivity. Starting from complexes of type 21, the intramolecular version of this reaction affords bicyclic products of type rac-20 (Scheme 7) [9]. 

Ground-state triplet dicarbenes in photochemical systems have also been extensively studied by ESR. Dowd and coworkers (304) examined the interesting, frequently postulated ground triplet trimethylenemethane obtained by photolysis of either 4-methylene-A -pyrazoline or a single crystal of 3-methylene-cyclobutanone. This triplet molecule is axially symmetrical and the proton hyperfine splittings of 8.9 gauss observed in single-crystal experiments indicate that all protons in the molecule are equivalent when the axis perpendicular to the plane... 

The photochemistry of cyclobutanones possessing a spiro-fused three-membered ring at the a-position has also been reported (15b). Spiro[2.3]hexan-4-one[64a], for example, undergoes photolysis in methanol solution to cyclic acetals [65a] and [66a] in addition to 3-cleavage ester [67]. The dialkylated derivative [64b], on the other hand, affords ring-expanded acetals [65b] and [66b]... 

In addition to serving as substrates with which to further study the effects of various substituents on the photochemical transformations of cyclobutanones, 3-methylenecyclobutanones are capable of generating the theoretically interesting trimethylenemethane biradical species (32) by way of the photodecarbonylation reaction. Indeed, Dowd and Sachdev (33) observed a triplet ESR spectrum upon photolysis of 3-methylenecyclobutanone [69]... 

Irradiation of alkoxycarbene complexes in the presence of aUcenes and carbon monoxide produces cyclobutanones. A variety of inter- and intramolecular [2 + 2]cycloadditions have been reported. The regioselectivity is comparable with those obtained in reactions of ketenes generated from carboxylic acid derivatives. Cyclobutanones can be obtained with a high degree of diastereoselectivity upon reaction of alkoxy carbenes with chiral A-vinyloxazolidinones. For example, photolysis of (19) in the presence of (20) gives cyclobutanone (21) (Scheme 31). In addition to aUcoxycarbenes, carbenes having a thioether or pyrrole substituent can also be employed. Related intramolecular cycloadditions of y,5-unsaturated chromimn carbenes afford bicyclo[2.1. IJhexanones (Scheme 32). 

The products of the photolysis of cyclobutanone are CO, C2H4, CH2CO, as well as some 3-butenaP . The value of 0c2H4 is approximately equal to that of chjco In contrast to the results of Blacet and Miller , Klemm et found that the ratio (C3H6-t-cyclo-C3H6)/CO was 1.1 +0.1 at 3130 A and 100 °C for the C2H4/CO ratio they gave a value of 1.7+0.1. The quantum yield of 3-butenal was estimated to be 0.004. 

Reaction I (in a peculiar form), as well as reactions II, III and IV all occur in the photolysis of cyclobutanone, though the quantum yield of step IV is very low. The occurrence of reaction III in the photolysis of cyclopentanone was not reported however, in that of cyclohexanone and cycloheptanone again all four reactions seemed to take place. 

McGee also found the cyclopropane/propene ratio to decrease with increasing pressure in the photolysis of cyclobutanone. However, his data indicated that the change is entirely due to an increase in propene formation, while cyclopropane formation is claimed to be independent of pressure. McGee suggested, on the basis of these results, that propene and cyclopropane were not formed from the same excited state. The deuterium content of the olefin, formed in the photolysis of cyclopentanone-2,2,5,5-rf4, also indicates that the hot cycloalkane is not the only source of the CH2 = CH(CH2) 4CH3 product - . 

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