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DOI: 10.1055/sos-SD-026-00451

Salaün, J.Science of Synthesis, (200526641.

β,γ-Unsaturated ketones undergo a formal [1,2]-acyl shift from the lowest excited triplet state to give cyclopropyl ketones in high yields; this is sometimes termed an oxa-di-π-methane rearrangement.[‌175‌,‌176‌] Thus, acetone-sensitized irradiation of S-β,γ-unsaturated ketone 206 gives the R-cyclopropyl ketone 207 with 90% conversion (Scheme 72).[‌177‌] The optical purity of R-cyclopropyl ketone 207 is greater than 90% demonstrating its photo­stability. Due to the rearrangement occurring with inversion of configuration at the α-carbon, the excited state follows the allowed π2a + σ2a pathway.[‌177‌]

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