Enone cycloadditions

A very remote secondary H/D isotope effect has been measured for the 2 + 2-cycloaddition of TCNE to 2,7-dimethylocta-2,fran -4,6-triene. The reaction of nitric oxide with iV-benzylidene-4-methoxyaniline to produce 4-methoxybenzenediazonium nitrate and benzaldehyde is thought to proceed via a 2 + 2-cycloaddition between nitric oxide and the imine double bond. A novel mechanism for the stepwise dimerization of the parent silaethylene to 1,3-disilacyclobutane involves a low-barrier [1,2]-sigmatropic shift. Density functional, correlated ab initio calculations, and frontier MO analysis support a concerted 2 + 2-pathway for the addition of SO3 to alkenes. " The enone cycloaddition reactions of dienones and quinones have been reviewed. The 2 + 2-photocycloadditions of homochiral 2(5H)-furanones to vinylene carbonate are highly diastereoisomeric. ... 

Enone cycloadditions, 44, 2 Enzymatic reduction, 52, 2 Enzymatic resolution, 37, 1 Epoxidation ... 

It is fortunate that the kinetic complexities and mechanistic ambiguities in enone cycloadditions, which promise to remain with us for some time, have not prevented some really elegant synthetic applications 140,142,150,151). 

Enone Cycloadditions and Rearrangements Photoreactions of Dienones and Quinones... 

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