Silyl Paterno Buchi reaction

This peculiar stereoselectivity might be attributed to a memory effect from the approach geometry between the triplet excited benzaldehyde and the alkene. Abe and coworkers have also observed a comparable stereochemical effect in the Paterno-Buchi reaction of 4-cycanobenzalde-hyde with O-silylated thioketene acetals 129 (Sch. 43) resulting in the highly functionalized oxetanes 130 [64]. 

Abe, M., Tachibana, K., Fujimoto, K., Nojima, M. Regioselective formation of 3-selanyl-3-siloxyoxetanes in the Paterno-Buchi reaction of silyl 0,Se-ketene acetals (0,Se-SKA). Synthesis 2001, 1243-1247. 

Bach, T., Jodicke, K., and Wibbehng, B., Reversal of the facial diastereoselectivity in the Paterno-BUchi reaction of silyl enol ethers carrying a chiral substituent in a-position. Tetrahedron, 52, 10861,1996. 

The Paterno-Buchi photocycloaddition of silyl 0,X-ketene acetals (with X—O, S, Se) and aromatic aldehydes was intensively investigated by Abe and coworkers in the last decade [62]. The regioselectivity of the reaction (71 vs. 72) is highly affected by the heteroatom (Sch. 19) [63,64]. The regioselectivity is rationalized by (a) the relative stability of the 1,4-biradicals and (b) the relative nucleophilicity of sp2-carbons in the respective 0,X-ketene acetal. 

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