Oxetane formation, Paterno-Biichi reaction

Carbonyl Compounds Oxetane Formation (Paterno-Biichi Reaction)... 

With many other ketones and aldehydes, reaction between the photoexcited carbonyl chromophore and alkene can result in formation of four-membered cyclic ethers (oxetanes). This reaction is often referred to as the Paterno-Biichi reaction.127 128 129... 

The concentration dependence of the photocycloaddition of cis- and trans-cyclo-cocetene 136 with aliphatic aldehydes was studied in order to test the spin-selectivity with respect to the cis/trans oxetane ratio and/or the eftdo/exo-selectivity relevant for the cis-photoadduct [156]. The results indicate a moderate but still significant spin correlation effect in the Paterno-Biichi reaction of cyclo-octene with aliphatic aldehydes. The exo-diastereoisomers were formed with similar probability as the e do-diastereo-isomers in the singlet carbonyl manifold, whereas the triplet excited aldehydes preferred the formation of the e Jo-diastereoisomer and trans fused products. 

The Paterno-Biichi reaction between excited carbonyl groups and olefins leads to the formation of four-membered cyclic ethers (oxetanes). This reaction has been reviewed by Arnold [94], Jones [95], Wilson [96]. The scope of the Paterno-Buchi reaction is impressive. It might be initiated by either singlet or triplet, n, re or, less frequently re, n excited carbonyls, and both electron-rich as well as extremely electron-poor olefins participate. It is now widely accepted that the initial intermediate in the oxetane formation is an exciplex between the excited carbonyl triplet and the olefin. The exciplex is then thought to decay to the triplet 1,4-diradical which, upon ISC to the singlet diradical, may either fragment back to the starting components or cyclize to oxetanes. 

Funke, C. W., Cerfontain, H. Photochemical oxetane formation the Paterno-Biichi reaction of aliphatic aldehydes and ketones with alkenes and dienes. J. Chem. Soc., Perkin Trans. 2 1976, 1902-1908. 

An extensive review of the selective formation of oxetanes using photochemical 2 + 2-cycloaddition reaction (Paterno-Biichi reaction) has been published. Methods that describe the control of stereo- and regio-selectivity of synthetically important oxetanes have been discussed. The bicyclic guanidine, l,5,7-triazabicyclo[4.4.0]dec-5-ene, catalyses the 2 -l- 2-cycloaddition of allenoates with trifluoromethylaryl ketones to yield highly substituted 3-alkyl-oxetan-2-ylidenes in high yields. ... 

Another photocycloaddition reaction that has been known for a long time is the Paterno-Biichi reaction, which involves the formation of oxetanes through the addition of an excited carbonyl compound to olefins ... 

Oxetane formation from (n,7C ) have also been reported. The reaction differs from the usual Paterno-Biichi reaction because the olefin is highly electronegatively substituted. 

The photocycloaddition of triplet benzophenone to norbornene was originally reported by Scharf and Korte. The photoproduct 101 that is formed in high exo-selectivity could be thermally cleaved to the 5,e-unsaturated ketone 102, an appHcation of the carbonyl-olefin metathesis (COM) concept. The 1,4-biradical formed in the interaction of norbornene with o-dibenzoyl-benzene was trapped in an intramolecular fashion by the second carbonyl moiety. A highly regioselective reaction of triplet benzophenone was reported with 5-methylenenorborn-2-ene, with preferential attack toward the exo CC double bond. A number of publications have discussed the photocycloaddition reactions of triplet carbonyl compounds to norbornadiene and quadricyclane, as weU as the competition between the Paterno-Biichi reaction and the sensitized norbornadiene/quadricyclane interconversion. Oxetane formation has also been reported for the photoreaction of biacetyl and para-quinones with benzvalene. ... 

Abe, M. and Nojima, M., The Paterno-Biichi photocydoaddition reactions of silyl ketene acetals controlling factors on the regio- and stereoselectivity in the oxetane formation,/. Synth. Org. Chem. Jpn., 59, 855, 2001. 

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