CYCLOMETALATION OF INDOLE-DERIVATIVES - CYCLOPALLADATION OF GRAMINE AND 1-METHYL GRAMINE AND CO INSERTION

Li2PdCl4, in methanol, with gramine 1 and 1-methyl gramine 2 gave the dimeric complexes 1a and 2a with chlorine bridges and having the indol e nucleus metallated at position 2. The corresponding bromo derivative s 1b and 2b were isolated from the reactions of Pd(OAc)(2) with 1 and 2, followed by treatment with LiBr. Complexes 1a,b and 2a,b gave the m onomeric, cyclometallated derivatives 3a-d by reaction with PPh(3) in methylene chloride. When the cyclopalladation of I-methyl gramine 1 wa s attempted by reacting PdCl2, PPh(3) and 2 in methanol in the presenc e of AcONa, an unexpected compound 4 was obtained. A structural determ ination of 4 showed it consisted of the known [Pd(PPh(3))Cl-3](-) anio n packed with the dimethyl-bis(3-methylene-1-methyl indole) ammonium c ation. When compounds 1a and 2a were reacted with carbon monoxide at a tmospheric pressure in methanol or ethanol and in the presence of NEt( 3), the corresponding 2-carboalkoxy indole derivatives 5 and 6 were is olated in high yields.