Carbene insertion into [2.2]metacyclophane-1,10-dione: a convenient route to [3.2]- and [3.3]-metacyclophanes

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Abstract
Ring enlargement of [2.2]metacyclophane-1,10-dione (1) with diazomethane conveniently affords [3.2] and [3.3]-metacyclophanes. The homologues [3.2]metacyclophane-1,11- and -2,11-diones (2a and b), thus obtained, were used for the synthesis of [3.2]metacyclophane-1,10-diene (5) and the parent hydrocarbon [3.2] metacyclophane (4). [3.3] Metacyclophane-1,12-, -1,11-, and -2,11-diones (6a-c), prepared by regioselective carbene insertion into (2a) and (2b) with diazomethane, served as intermediates in the synthesis of [3.3]metacyclophane (8). The reactivity of the carbonyl groups of oxometacyclophanes decreases with ring size and thus correlates with ring strain. In contrast to (6a-c), the [3.2]metacyclophanediones (2a and b) form hemiacetals when dissolved in methanol.

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