Cerium(IV) oxidation of 1,2,3,4-tetrahydronaphthalene lignans

Ipso-nitration was confirmed by the reaction of dimethylanhydro-alpha-conidendryl alcohol (1) and dimethylanhydro-beta-conidendryl alcohol ( 2) with ceric ammonium nitrate (CAN) in neat HOAc. Reaction of compound 1 and 2 with CAN in neat HOAc gave mono and dinitroburseran-type lignan acetates. Oxidation of compounds 1 and 2 with other Ce(IV) reagents was also explored. Reaction of compound 1 and 2 with cerium (IV) pyridinium nitrate (CPN), cerium (IV)-3,5-dimethylpyrazolium nitrate (CDPN) and cerium (IV)-4-dimethylaminopyridinium nitrate (CDMAPN) in HOAc also confirmed ipso-nitration. Furthermore, reactions of 1 and 2 with CDPN in propionic acid afforded the nitroburseran type-lignans as propionate esters.;The structural requirements for ipso-nitration with CAN was studied by reacting high and low electron density model compounds with CAN. The yield in many cases was small and complete analysis of the crude product was not made in some cases. However, analysis of the isolated products or the GC/MS of the crude product demonstrated the following results. The low electron density model compounds, gave one or more products mainly from benzylic oxidation. From the high electron density model compounds, 3,3 '4,4'-tetramethoxydiphenylmethane ( 86), 1-(4-methoxyphenyl)-6,7-dimethoxy-1,2,3,4-tetrahydronaphthalene (95) and, 2-methyl-3',4',4,5-tetramethoxy diphenylmethane (87) gave at least one of the products due to ipso-nitration followed by debenzylation. The formation of benzophenone (72) from triphenylcarbinol (114) and (3,4-dimethoxy)-diphenylmethane (91) is assumed to be due to oxidative cleavage and not ipso-nitration. The results of oxidation with CAN of the various compounds studied showed that ipso-nitration and debenzylation take place only when a diphenylmethane unit is part of the model compound. Both aromatic rings should be well substituted by electron donating groups. Also, when these structural conditions are met, ipso-nitration takes place at the more substituted aromatic ring.;The yield of the esters prepared by benzylic oxygenation of simple diphenyl-methanes with CAN in various carboxylic acids seemed to depend on the type and size of the carboxylic acid used. C2-C5 Straight chain carboxylic acids gave esters yields ranging from 58% to 100% while hexanoic acid gave 40% on oxidation of 106.