Active MnO2. Oxidative Dehydrogenations

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Abstract
We recently required substantial quantities of 5,8-disubstituted naphthoquinone IV as a precursor for the synthesis of a cyclophane. The sequence chosen to provide the necessary intermediate (IV) utilized a Diels-Alder reaction, between I and p-benzo-quinone, followed by aromatization. Several attempts however at dehydrogenating adduct II (Br2;2 air;3 DDQ or chloranil4) failed, or afforded poor conversions (10–25%). During our research, a report appeared describing the use of commercial grade MnO2in the oxidation of hydroquinones to quinones. 5 Encouraged by the results described in the publication we attempted the oxidation of II with MnO2. When adduct II was stirred in benzene with ordinary MRO2