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Metalla-cycloaddition: An unprecedented formal [4+2] cycloaddition reaction takes place when osmium hydrido alkenylcarbyne 1 reacts with acetonitrile to afford the first metallapyridinium complex 2 in high yield (see scheme). Deprotonation of 2 gives the first osmapyridine compound 3. Treatment of 3 with HBF4 can regenerate 2 in almost quantitative yield.
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Liu et al. (2009) studied this question.
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