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An iridium atom in a bridgehead position is the most unusual feature of 2, which was obtained in place of the anticipated carbene vinylidene complex upon reaction of 1 with propiolic acid. Equally surprising is the fact that 2 must be regarded as an oxonium system rather than as a carbene, the most obvious resonance alternative. R CO2CH3.
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O’Connor et al. (1990) studied this question.
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