Chem. Pharm. Bull. 55(10) 1540—1543 (2007)

biological structures and functions. It is suitable for the analysis of biological interactions because it is based on the affinity of the ligand moiety. Various photophors, such as phenyldiazirine, arylazide and benzophenone, were used. Comparative irradiation studies of these three photophors in living cells suggested that a carbene precursor, (3-trifluoromethyl) phenyldiazirine, is the most promising, but complicated synthesis of the diazirinyl three-membered ring prevented the application of the photophor. Post-functional synthesis of TPD derivatives is one of problems to be solved. It is well known that catalytic transfer hydrogenation followed by Wittig reaction is a useful method for general purpose carbon elongation, but the synthetic route does not apply for diazirinyl compounds, because it was reported that the diazirinyl nitrogen–nitrogen double bond was not tolerated under a hydrogen atmosphere in the presence of Pd–C for more than 1 h. Although the selective hydrogenation of alkene in diazirinyl and other photophors containing photo ligand in the presence of Pd/C was reported very recently, the hydrogenation of diazirinyl derivatives is low yield compared with other photophors due to the presence of the homogeneous N N double bond. Furthermore, the applications of the method were not reported. Wilkinson’s catalyst (RhCl(PPh3)3) was used as a homogeneous catalyst for alkene hydrogenation. The catalyst seems suitable for catalytic hydrogenation in diazirinyl compounds, because we have already established that the triphenylphosphine moiety does not affect diazirinyl compounds and it was reported as a selective carbon–carbon double bond over a heterogeneous multiple bond (nitro, carboxylic acid, and ester). We will describe selective hydrogenation of the carbon–carbon double bond in the presence of a nitrogen–nitrogen double bond in diazirinyl moiety with Wilkinson’s catalyst. Diazirinyl cinnamyl derivatives were prepared from aldehydes 1 and 2 with corresponding Wittig reagents in moderate yield (Fig. 1). The reaction afforded predominantly trans isomer calculated by H-NMR signals. Ethyl esters 3a and 4a were hydrolyzed with aqueous sodium hydroxide to afford cinnamic acid derivatives Selective hydrogenation of diazirinyl compounds with Wilkinson’s catalyst was examined in THF-tert-butanol or methanol in a similar manner as described in the reference (Fig. 2). Little difference was observed between these two solvents. The results gave the hydrogenated proportion of the reaction mixture, which was directly monitored by H-NMR in CD3OD. Table 1 shows the degree of hydrogenation of typical compound 3a with various amounts of Wilkinson’s catalyst at room temperature. Although slightly larger amounts of the catalyst than in 1540 Vol. 55, No. 10