Cross-conjugated s. Dienones

Cross-conjugated s. Dienones, cross-conjugated Cross-coupling with Grignard compds. 26,875... 

Cross-conjugated cyclic dienones with 6-, 7-, and 8-membered rings exhibit a rich and diverse photochemistry. The deep-seated photochemical rearrangements found in these systems have attracted numerous mechanistic studies. Cydohexadienones have received the most attention and provide the general framework for the mechanistic understanding of the photochemistry for this class of compounds. The key intermediate in these systems is an oxyallyl transient that is formed by ring closure across the P, P -carbons in the dienone s) tems A —> B. 

As just described, Zimmerman has reported one instance of a dienone rearrangement which definitely does not fit Chapman s general picture. Schuster has provided two reports410,411 of cross-conjugated cyclohexadienones which eliminate radical species. With the trichloro-methyl-substituted ketone 34, both cleavage to the cresol and rearrangement to lumiproduct are quenched by dienes.411 Stern-Volmer quenching plots indicate that the rate at which the excited triplet reacts exceeds 10° sec"1 for both reactions.412... 

A soln. of 2-methyl-l-methoxymethyl-3-morpholinobuta-1,3-diene in THE added slowly under argon to 2 eqs. benzaldehyde and MgBr2 Et20 in the same solvent with ice-cooling, the mixture allowed to warm to room temp., stirred overnight (12 h), then hydrolysed with 50% aq. AcOH for 1 h - product. Y 68%. F.e.s. J. Barluenga et al., J. Chem. Soc. Chem. Commun. 1988,1247-9 cross-conjugated dienones in acetonitrile cf. Tetrahedron Letters 30, 1413-6 (1989). 

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