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Eight, not six: The intramolecular frustrated Lewis pair 1 reacts with conjugated enynes and diynes by 1,4-addition to yield the corresponding eight-membered cyclic allenes 2 and cumulenes 3, respectively. The thermodynamically more favorable 1,2-addition (formation of six-membered-ring products) is not observed, which indicates that the observed addition is a kinetically controlled reaction.
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Momming et al. (2010) studied this question.
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