Synthesis of sterically congested acetic acid derivatives: The reaction of hindered α-oxo esters with pentasubstituted aryl Grignard reagents

Article abstract of DOI:10.1055/s-1993-25911

The reactions of pentamethylphenylmagnesium bromide and pentachlorophenylmagnesium chloride with tert-butyl 2-oxo-3,3-dimethylbutanoate to give the 2-aryl-2-hydroxy-3,3-dimethylbutanoate esters were investigated. Attempted acid catalysed dealkylation of the tert-butyl 2-hydroxy-3,3-dimethyl-2-(pentamethylphenyl)butanoate to the corresponding acid was accompanied by skeletal rearrangement, while the corresponding pentachlorophenyl ester reacted normally. The corresponding α-pentachlorophenyl α-tertbutyl acetic acid 15 was synthesised without rearrangement. The reaction of pentachlorophenylmagnesium chloride with diisopropyl oxalate gave the α-oxo ester 18, which reacted with pentamethylphenylmagnesium bromide to afford the unsymmetrical diarylacetate ester 22. The corresponding acid chloride 25 could not be converted to the interesting unsymmetrical diarylketene 26.