The Oxa Di-n-methane Reaction and Related Processes

1 The Oxa Di-n-methane Reaction and Related Processes - A detailed examination of the triplet and singlet state reactions of a series of P,y-unsaturated enones has been reported. Many examples are cited and are typified by the conversion of the enone (140) into (141) on sensitized irradiation. This reaction is a typical example of the well known oxa-di-n-methane process, which fundamentally involves a 1,2-migration of the acyl group. Direct irradiation populates the singlet state of the enone (140) and this yields (142) by a 1,3-acyl migration. The oxa-di-n-methane reaction of chiral bicyclo[2.2.2]oct-5-en-2-one systems has been used as a path to tricyclic ketones. 

1 PhotoreactifHis of Pyridones - Previously Sieburth and his colleagues have demonstrated that the photochemical cyclization of tethered pyridones such as 

The X-ray crystal structures of a series of Dewar pyrimidones (151), obtained by the irradiation of the pyrimidones (152), have been determined. The photochemical reactivity of l-methyl-4,6-diaryl-2(///)pyrimidinone derivatives in the presence of various thiols has been studied.  

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The Oxa-Di-n-methane reaction and Related Processes. Interestingly, some P,y-unsaturated ketones do not undergo 1,3-acyl shifts or the oxa-di-Ti-methane rearrangement. An example of this is compound (61), which on irradiation undergoes only a Norrish Type II hydrogen abstraction. ... 

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