Oxidation of 1-Benzoylpyrrole and 1-Aroylindoles by Palladium Acetate

Oxidation of l-benzoylpyrrole and l-aroylindoles by palladium acetate in acetic acid gave the corresponding ring-closed products and dimerized compounds.Oxidative coupling of arenes and olefins by palladium(I1) salts is well known as a useful method for synthesis of aryl-substituted olefins.' Oxidation of olefinic compounds linked through carbon unit to aryl groups by palladium(I1) salts is, therefore, expected to result in intramolecular ring-closure.The reaction is applicable to synthesis of polycyclic heterocycles.Furthermore, we have already reported the intermolecular oxidative coupling of aromatic heterocycles such as l-substituted pyrroles and indoles and arenes by palladium(I1) acetate.'These observations led us to examine ring-closure of l-benzyl-and l-benzoylpyrrole and indoles by palladium(I1) acetate, depicted in Scheme 1. Scheme 1 Ac~, , OAC __L R -Pd R X X -2 AcOH X = H2 or 0 X Although oxidation of l-benzylpyrrole and -indole by palladium acetate in acetic acid gave complex reaction mixtures, the treatment of l-benzoylpyrrole and l-aroylindoles gave expected ring-closed products together with dimerized compounds.This paper describes the oxidation of l-benzoylpyrrole and l-aroylindoles such as l-benzoyl-, l-(4-methylbenzoy1)-. l-(l-naphthoy1)-, and l-(2-naphthoy1)-indoles, Treatment of l-benzoylpyrrole (1) with palladium acetate in acetic acid gave a -2 ring-closed product ( z ) , dimerized compounds (3) and (4).and benzoic acid.--9-~ethyl-ll-(l-(4-methylbenzoyl)indol-3-yl]-6~-isoind0lo(2,l-a]indol-6-one (7h) -Mp 203-205 'C: IR (Nujol) 1710, 1675, 1610 cm-l: 'H-NMR (CDC13) QZ.lO(s, 3H), 2.39 ( s , 3H), 6.63(d, 28, J=8 Hz), 6.96-7.83(m,13H), 8.04-8.25(m,1H): MS m/z ( 8 ) 467 ( ~+ + l , 14).466(~+, 38), 119(100), 91(23).Anal.Calcd for C32X22N202: C, 82.38; H, 4.75; N, 6.01.Found: C, 82.11; H, 4.60; N, 5.99.6~-~aphtho[l', 2' :3,4)pyrrolo(1,2-a) indol-+one (6c) -Mp 216-218 OC: IR (Nujol) 1710, 1595 cm-l: 'H-NMR (CDC13) S6.57(s, 1H).7.03-8.04(m, 9H), 8.8-9.03(m,1H): MS m / z (%) 270(Mf+l, 21), 269(~+, loo), 240(18), 135(12).Anal.Calcd for C19W11NO: C, 84.74; H, 4.12; N, 5.20.Found: C, 84.61; H, 3.99; N, 5.21.6H-Naphtho(2' ,3' :3,4]pyrrolo(l,2-a)indol-6-one (6d) -Mp 246-248 OC: IR (Nujol) 1725 cm-l: 'H-NMR (CDC13) s6.67(s, lH), 7.1-8.l(m,8H).7.89(s, lH), 8.26(s, 1H) : MS mjz (%) 270(~++l, 22), 269(~+, loo), 24O(ZO), 135(l3).