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Synthesis 1993; 1993(6): 606-610
DOI: 10.1055/s-1993-25911
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Synthesis of Sterically Congested Acetic Acid Derivatives: The Reaction of Hindered α-Oxo Esters with Pentasubstituted Aryl Grignard Reagents

A. F. Hegarty* , P. O'Neill
  • *Chemistry Department, University College Dublin, Dublin 4, Ireland
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Publication Date:
17 September 2002 (online)

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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-α-tert-butyl 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.