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The Diels-Alder reaction of 2-substituted 4-(trimethylsilyloxy)oxazoles, which were prepared in situ from trimethylsilyldiazomethane and acyl isocyanates, with dimethyl acetylenedicarboxylate or ethyl propiolate gave furan-3,4-dicarboxylic or furan-3-carboxylic esters in good yields.
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Aoyama et al. (2004) studied this question.
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