Oxetan Formation

The gas-phase irradiation of hexafluoroacetone and 1,2-dichlorofluoroethylene (mixture of Z and E isomers) gives the two oxetans (86) and (87) in a ratio of 

Photoaddition of benzophenone to the methylene ketone derivatives (88) yields the oxetan derivatives (89a) in 28 and 26% yield, respectively. The biradical (90) is presumed to be the intermediate in the formation of these compounds. The authors suggest that there are two competing pathways for reaction within this biradical, one leading to the oxetans (89), and another by rearrangement through 

A detailed study of the photoaddition of tran -dicyanoethylene to the ketones (99—101) has been published. The results indicate that the cycloaddition is 

Reasonable yields of the adducts (103) are obtained when acetone is irradiated in the presence of 2,3-dihydro- and 2-methyl-2,3-dihydro-furan. Compounds of this structure can also be obtained by the photocyclization of the vinyloxy ketones (104a) and (104b),. which yields the adducts (105a) and (105b), respectively. Intramolecular cycloaddition is also encountered in the photoreactions of the cyclic alkanones (106). However the reaction favours the formation of the crossed adduct (107) in all the cases studied. The accompanying products are the alternative oxetan (108) and the products from Norrish Type I fission. 

The photochenical addition of benzaldehyde to cyclic alkenes (62, 63) has been studied. The products produced from these reactions are the oxetans shown in scheme 7. In addition to the 

However, the important result from this study relates to the stereochemistry of the oxetans. Thus, there is a preference in all of the cases studied for the formation of the encfo-isomer and the ratios obtained are shown under the appropriate structures. 

The authors reason that the preference shown is attributable to 

Kagan et ai. reported that the irradiation of neat acetone 

and t-Bu) on irradiation in acetonitrile and aqueous solutions of 0-cyclodextrin with fumaronitrile. The influence of environment on the formation of the syn- and the anti-oxetans (76) and (77) respectively was studied. 

The mixture of products (87) and (88) is formed on irradiation of furan and benzophenone in benzene at 0°C. The structures of the products were established by X-ray and by chemical and spectral studies. Biacetyl adds photochemically to the 

Abdul et al. have reported the remarkable isomerization of the ketone (100) into the compound (101).  

The benzoxazinone (107) deceu-bonylates to yield (108) on irradiation. Photodecarboxylation of (109) provides a route to exaltolide The photochemical decarboxylation of the lactones (110) provides a convenient method for the synthesis of 1-azabicyclobutemes (ill). The reaction is, however, restricted to those compounds with two aryl groups on C-2. The norbornadienone (112) has been produced in a matrix by the irradiation of the azo compound (113). These authors point out that the outcome of the irradiation is dependent to a large extent on the material of which the matrix is composed.  

Acknowledgements.- 1 would like to express my sincere thanks to Dr. Stephen Bell and to Mr. Mike Whitehead of the Department of Chemistry and the Computing Centre respectively of the University of Dundee for invaluable assistance with the computer compiling programs used in these reviews. 

Fetizon, H. Colin, and J.-C. Diez-Masa, J. Chem. Soc., Chem. Common., 

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With aromatic carbonyls, oxetane formation appears to arise from the carbonyl triplet state, as evidenced by quenching studies. For example, benzaldehyde irradiated in the presence of cyclohexene yields products indicative of hydrogen abstraction reactions and an oxetane ... 

The reaction of carbonyl compounds to olefins often yields products difficult to obtain synthetically by other routes. The excellent yields obtainable under proper conditions make this reaction of definite preparative interest. Examples of some synthetic applications of oxetane formation follow ... 

For oxetane formation from formaldehyde and ethylene, we should consider the following four transition states and intermediates for the reaction<181) ... 

Yang has observed that cis-trans isomerization of 3-methyl-2-pentenes is accompanied by oxetane formation and concluded that intermediates such as (22) are common to both isomerization and oxetane formation/825 Deuterium isotope effects are also consistent with the involvement of this type of intermediate/83,845 ... 

The other photochemical reactions of simple carbonyls mentioned earlier in this chapter—type I cleavage (a-cleavage) and oxetane formation—will be discussed in Chapter 4. 

The Photochemistry of Simple Carbonyl Compounds Type I Cleavage and Oxetane Formation... 

In Chapter 3 we discussed two photochemical reactions characteristic of simple carbonyl compounds, namely type II cleavage and photoreduction. We saw that photoreduction appears to arise only from carbonyl triplet states, whereas type II cleavage often arises from both the excited singlet and triplet states. Each process was found to occur from discrete biradical intermediates. In this chapter we will discuss two other reactions observed in the photochemistry of carbonyls, type I cleavage and oxetane formation. 

Table 4.10. Reactivity of Various Aromatic Carbonyls toward Oxetane Formation and Photoreduction Compared to the Nature of the Lowest TripletiB3,9 Bm...

In a recent study of intramolecular oxetane formation in naphthoylnor-bornenes Sauers and Rousseau provided evidence that two distinct excited states are involved<99) ... 

Lange and Bosch<109) reported the interesting intramolecular oxetane formation shown below. Reduction with lithium aluminum hydride afforded m is-9-decalol (32%) ... 

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