Propargylic carbonate reaction with malonate

No reaction of soft carbon nucleophiles takes place with propargylic acet-ates[37], but soft carbon nucleophiles, such as / -keto esters and malonates, react with propargylic carbonates under neutral conditions using dppe as a ligand. The carbon nucleophile attacks the central carbon of the cr-allenylpal-ladium complex 81 to form the rr-allylpalladium complex 82, which reacts further with the carbon nucleophile to give the alkene 83. Thus two molecules of the a-monosubstituted /3-keto ester 84, which has one active proton, are... 

Type III reaction proceeds by an attack of a nucleophile at the central sp carbon of the allenylpalladium. Soft carbon nucleophiles such as / -keto esters and malonates react with propargylic carbonates under neutral conditions using DPPE as a ligand [35], The 2,3-disubstituted propenes 151 and 152 are obtained by the reaction of 2-propynyl carbonate (145) with two moles of malonate under neutral conditions in... 

In addition to softer neutral nucleophiles, harder anionic nucleophiles also alkylate the r/3-allcnyl/propargyl central carbon. The rhenium 7 3-2-butynyl complex reacts with malonate and lithium ferZ-butylacetylide to give rhenacyclo-butene complexes (Scheme 31) <1998JA722>. The reaction of sodium amide with an r/ -allenylplatinum complex similarly yields the platinacyclobutene complex, which does not further equilibrate (Equation 60) <1998JOM39>. 

Scheme 11.48 Mechanism of the reaction of propargyl carbonate with malonate.

In contrast to facile Pd(0)-catalyzed reactions of allyl esters with soft carbon nucleophiles via r-allylpalladium intermediate, propargyl esters such as acetate are less reactive toward soft carbon nucleophiles. However, /3-keto esters and malonates react under neutral conditions with propargyl carbonates using DPPE as a ligand [37], Acetoacetate reacts with meAyl propargyl carbonate (119) in THF at room temperature to afford 4-(methoxycarbonyl)-5-methyl-3-methylene-2,3-dihydrofuran (120) in 88 % yield. The furan 121 was obtained by isomerization of the methylenefuran 120 under slightly acidic conditions. 

When the reaction conditions were applied to allylic carbonate 8, the palladium-mediated cyclization occurred to form the 11-membered ketone 9 in 86% yield (eq 30). When the palladiun-catalyzed allylation of propargyl malonate 10 in the presence of BSA was combined with the rhodium-catalyzed Pauson-Khand t)fpe reaction, the tandem action of the two catalysts gave an excellent yield (92%) of bicyclopentenone 11 in one-pot (eq 31). ... 

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