Novel Synthesis and Properties of 1,6-Methanocycloundeca[b]pyrimido[5,4-d]pyrrole-12,14-dione Derivatives: Autorecycling Oxidation of Some Amines and Alcohols

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Abstract
Novel 1,6-methanocycloundeca[b]pyrimido[5,4-d]pyrrole-12,14-dione derivatives 6a,b and 7a − c were synthesized in moderate to good yields by the enamine alkylation and dehydrating condensation reactions of 11-chloro-3,8-methano[11]annulenone (8) with 6-amino-3-substituted uracil derivatives and subsequent elimination of HCl. The 1H NMR spectra clarified that compounds 6a,b and 7a − c are aromatic molecules having a diatropic π-system, which is suggested by the chemical shifts of the bridge methylene protons and peripheral protons. The electrochemical reduction exhibited more positive reduction potentials as compared with those of the vinylogous compounds of cyclohepta[b]pyrimido[5,4-d]pyrrole derivatives. In a search for the oxidizing function of 6a,b and 7a − c, compounds 6a and 7b were demonstrated to oxidize benzylamines, cyclohexylamine, and benzyl alcohol to give the corresponding carbonyl compounds in more than 100% yield under aerobic and photoirradiation conditions, while only benzylamine was oxidized under aerobic and thermal conditions at 100 °C. Thus, compounds 6a and 7b oxidize amines and alcohols in an autorecyling process, and the efficiency is higher under photoirradiation as compared with the thermal process, suggesting the oxidation reaction probably proceeds via electron transfer from amine and alcohol to the excited and ground states of compounds 6a and 7b.

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