Successive [4 + 2] cycloadditions of dimethyl 1,2-cyclobutadienedicarboxylate (1), first with itself and then with the next highest adducts 2 and 3, result in the [7]-ladderane 4. The [n]-ladderanes 2–4 are of interest because of their weak σ framework and the very different polarities of the two sides of the molecule. R = CO2Me.
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Mehta et al. (1992) studied this question.
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