Extremely mild conditions are required for an intramolecular thermal [2+2] cycloaddition in the swivel-cruciform molecule 1. As a result of the relatively free rotation about the biphenyl bond in 1 (see picture, left) a conformation is accessible in which the alkene bonds of the two ortho substituents are brought into proximity in the required orthogonal arrangement, and the intramolecular cycloadduct (right) is formed at room temperature.
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Tian et al. (2007) studied this question.
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