Phenyl ethers reactions with 1.3-dicarbonyl

After these initial results by Tsuji, this elementary step was incorporated into a catalytic process by Hata and co-workers at Toray Industries and by Atkins and co-workers at Union Carbide. These groups reported reactions of allylic phenyl ethers, allylic alcohols, and allylic acetates with carboxylates, alcohols, primary and secondary amines, and methyl acetoacetate catalyzed by Pd(0) complexes and precursors to Pd(0) complexes (Equation 20.3). - After these initial reports, early developments focused on reactions of "soft" carbanions derived from 3-dicarbonyl compounds, cyanoesters, and related compounds containing two electron-withdrawing groups attached to the nucleophilic carbon. Although these reactions occur with allylic halides in the absence of a catalyst, these reactions are greatly accelerated by palladium catalysts. Thus, the palladium catalyst allows these reactions to occur under mild conditions with allylic acfetates, which are more accessible than allylic halides, and with selectivities that are altered by the metal catalyst. 

Kita et al. further developed PIFA-induced CDC reactions between phenyl ether derivatives and cyclic 1,3-dicarbonyl compounds as nucleophiles (Scheme 8.2). The reactions with 1 equiv. of PIFA in hexafluoro-2-propyl alcohol attach nucleophiles onto the ort/jo-position of para-substituted phenyl ethers to afford the dehydrogenative coupling products 8 in moderate yields. UV and electron spin resonance (ESR) spectroscopic studies support a reaction mechanism involving the formation of the charge-transfer complex 9 followed by the generation of the cation radical intermediate 10. This is the first example of the reaction of aromatic compounds with PIFA that involves the formation not of diatyliodonium(m) salt 11 but the cation radical intermediate 10 as a key intermediate. 

Reactions of unsymmetrical methylene 1,3-dicarbonyl compounds with enol ethers have been investigated by Yamauchi et al. [137]. As we have mentioned earlier, the a,/ -unsaturated ketone moiety in alkylidene-/ -ketoesters reacts exclusively as the oxabutadiene. However, high regioselectivity is also observed with mixed alkyl-phenyl-1,3-diketones with exclusive reaction of the aliphatic carbonyl group, whereas in alkylidene-1,3-dicarbonyl compounds bearing an aldehyde and a keto-moiety, the a,/J-unsaturated aldehyde reacts preferentially as oxabutadiene, but not exclusively [130a]. 

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