Electron-deficient olehn

For example, the acyl-aryloxo bond cleavage (type b) is shown by the reaction of Ni(cod)2 with phenyl propionate in the presence of PPhs (Scheme 3.34) or 2,2 -bipyridine [65]. The reaction products are ethylene, phenol, and (car-bonyl)nickel complex. Formation of these products is conveniently understood by initial oxidative addition of EtC(0)-0Ph followed by decarbonylation, )S-hydrogen elimination and reductive elimination, though (acyl)(aryloxo)nickel(II) intermediate is not isolated. However, such an intermediate is isolated by the selective insertion of CO into the (alkyl)(aryloxo)nickel (or palladium) complexes, which smoothly affords esters by reductive elimination promoted by electron deficient olehns. The results suggest that the oxidative addition involving C-0 bond cleavage is essentially reversible. 

Nan ya et al. (97) also reported the synthesis of isoindolediones by the reaction of miinchnones with 1,4-benzoquinones. Reactions with an unsymmetrical mtinchnone were not regioselective. Several groups have examined the reactions of miinchnones with unsaturated nitriles, including 2-chloroacrylonitrile (98), cinna-monitrile (78,99) and fumaronitrile (78) to give unexpected products in several cases. Eguchi and co-workers (100) smdied the cycloaddition of several mtinch-nones with electron-deficient trifluoromethylated olehns. Thus, miinchnones 176... 

Early extensive accounts of the Air participation of o, j3-unsaturated carbonyl compounds in [4 -I- 2] cycloadditions detailed their reactions with electron-deficient dienophiles including a,/3-unsaturated nitriles, aldehydes, and ketones simple unactivated olehns including allylic alcohols and electron-rich dienophiles including enol ethers, enamines, vinyl carbamates, and vinyl ureas.Subsequent efforts have recognized the preferential participation of simple a.jS-unsaturated carbonyl compounds (o, j3-unsaturated aldehydes > ketones > esters) in inverse electron demand [4 + 2] cycloadditions and have further explored their [4 + 2]-cycloaddition reactions with enol ethers, acetylenic ethers, ke-tene acetals, enamines, " ynamines, " ketene aminals, and selected simple olefins (Scheme 7-1). Additional examples may be found in Table 7-1. 

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