In this reaction photoinduced oxetane is formed by the photochemical [2+2] cycloaddition of a carbonyl with an olefin.
Mechanism:
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:
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.
Application:
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