Oxetan Formation and Addition Reactions

Kawase, S. Yamaguchi, H. Ochiai, and H. Horita, Bull. Chem. Soc. Japan, 1974,47,2660. 

Cantrell102 suggests that the triplet excited state of the acetylthiophen may be predominantly in character, rather than mr. This proposal is backed up by the observation that the long-lived phosphorescence at 77 is mr in character. Similar products are isolated from the reaction of the same ketone with isobutene. 

2-Benzoylthiophen gave the oxetan (146a) when it was irradiated with 2,3-dimethylbut-2-ene. Unstable oxetans (146b—d) are also obtained from the 

3-Aroylthiophens behave similarly. The oxetans were identified by n.m,r. spectroscopy but could not be isolated since they all lost formaldehyde to yield methylene derivatives. Surprisingly, although all the ketones give good yields of oxetans, only the 3-benzoylthiophen exhibits a lowest excited state of mr character from which oxetans are usually formed. The 2-benzoylthiophens exhibit lowest excited states with inr character, a conclusion which was also reached for 2-acetylthiophen.102 

Oxetans (147) have been reported to be produced from photochemical addition of 1-naphthaldehyde, 2-, 3-, and 4-benzoylpyridine, and 2-benzoylthiophen to 

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