[reaction--see text] Carboxylic acids possessing strongly electron withdrawing substituents in the alpha-position in the presence of DCC acylate sterically hindered and chemically sensitive alcohols. The pattern of reactivity, the deuteration experiments, and the formation of a product derived from a [4 + 2] cycloaddition reaction corroborate the existence of ketene intermediates in the reaction.
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Nahmany et al. (2001) studied this question.
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