Paterno-Büchi Reaction

The photochemical [2+2] cycloaddition of a carbonyl with an olefin to give an oxetane.

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Mechanism of the Paterno-Buechi Reaction

The possible transitions (C=O) are shown below:

Once the carbonyl ground state has been photoexcited, either a singlet or triplet state may be formed:

n,π*-transition

Either type of transition (n,π* and π,π*) and electronic state (singlet, triplet) may participate in the first stage of this reaction, which is rationalized by invoking diradical intermediates:

Breaking of the new σ-bonds requires more energy, and the reverse reaction is not possible using same light frequency.

Recent Literature

Paternò-Büchi Reactions of Silyl Enol Ethers and Enamides
F. Vogt, K. Jödicke, J. Schröder, T. Bach, Synthesis, 2009, 4268-4273.