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Trifluoroacetohydroximoyl bromide etherate (1) reacted with an excess of malononitrile in the presence of sodium methoxide, giving a fused isoxazolopyridine 3, participated by two molecules of malononitrile, along with the conventional isoxazole 2. Similar concomitant formation of 7 and the fused pyrazolopyridines 8 was also recognized from the hydrazonoyl bromides 6 and their product ratio was found to depend on the reaction conditions, particularly on the concentration of malononitrile used.
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Tanaka et al. (1987) studied this question.
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