Carboxylic Acid Derivatives as Nucleophiles

Backvall has reported the gold(III)-catalyzed cycloisomerization of allene-substituted malonic esters to form p,Y-unsaturated 6-lactones [115]. For example, treatment of allenyl malonate derivative 76 with a catalytic 1 3 mixture of AUCI3 and AgSbF in acetic acid at 70 °C led to isolation of 8-lactone 77 in 99% yield (Eq. (12.41)). The transformation was restricted to substrates that contained a terminally disubstituted allenyl moiety and presumably occurs via nucleophilic attack of the carbonyl oxygen atom on a gold-complexed allene followed by acetate-mediated demethylation and protodeauration. 

Shin has reported the gold(III)-catalyzed 5-endo cyclization of tert-butyl allenoates to form 2,4-disubstituted butenolides [116]. As an example, treatment of terf-butyl 2-benzyl-5-phenyl-2,3-pentadienoate with a catalytic amount of AUCI3 in dichloro-methane at room temperature for 1.5 h led to isolation of the butenolide 78 in 96% yield (Eq. (12.42)). The protocol tolerated a range of substitution at the allenyl carbon atoms. 

Gagosz has reported the stereoselective gold(I)-catalyzed isomerization of a-aHenyl esters to form l,3-butadien-2-ol esters [117]. As an example, treatment of a-aHenyl 

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