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Tricarbonylcyclohexadienyliron salts of type (2; R2=+), after reaction successively with a β-diketone or a β-keto-ester and manganese dioxide or lead dioxide, give tricarbonyl-cis-3a,7a-dihydrofuraniron complexes of type (3). Use of deuteriated intermediates indicated that the cyclisation occurs with specific loss of the 6-endo-proton.
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Birch et al. (1973) studied this question.
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