Facile synthesis of indolizinoindolone, indolylepoxypyrrolooxazole, indolylpyrrolooxazolone and isoindolopyrazinoindolone heterocycles from indole and imide derivatives.

Chemo-, regio- and diastereoselective coupling reactions of indole with imide derivatives leading to unique heterocyclic systems are demonstrated. Acid-induced 3-position coupling reactions of indole with cyclic imide derived lactamols followed by acid promoted 2-position cyclizations with the corresponding aldehydes are described to obtain the indolizinoindolones and benzoindolizinoindolones. Base induced 2-position coupling reactions of N-tosylindole with N-(2-iodoethyl)imides and the subsequent cyclizations provide indolylepoxypyrrolooxazole, indolylpyrrolooxazolone and indolyloxazoloisoindolone. Reductive cleavage of indolyloxazoloisoindolone to the corresponding alcohol followed by mesylation and base promoted N-cyclization affords the in situ air-oxidized pentacyclic product hydroxyisoindolopyrazinoindolone. A regioisomeric structural revision of the natural product from 1,2,5,6,7,11c-hexahydro-3H-indolizino[7,8-b]indol-3-one to 1,2,5,6,11,11b-hexahydro-3H-indolizino(8,7-b)indol-3-one is also reported in the present studies focussed on the methodologies for heterocyclic synthesis.

Regioselective oxidation of indoles to 2-oxindoles.

Facile regioselective oxidation of indoles to 2-oxindoles promoted by sulfuric acid adsorbed on silica gel is reported. The demonstrated practical site-selective heterogeneous oxidation reactions conveniently take place with a broad substrate scope and functional group tolerances. The present oxidation strategy is also employed to accomplish the total synthesis of natural products donaxaridine and donaxarine. On the basis of analytical and spectral data it is evidenced that donaxarine stays in equilibrium with its hydrated ring opened form. The structural features essential for this type of oxidation and plausible mechanism are discussed in brief.

Total Synthesis of Bioactive Canthine Alkaloid Cordatanine Comprising in Situ Double Oxidative Aromatization of Tetrahydrocarbazole.

Starting from tryptamine and methoxymaleic anhydride, concise and efficient total synthesis of cordatanine has been accomplished via regioselective reduction of methoxymaleimide, acid-catalyzed intramolecular cyclization of the formed lactamol, in situ stepwise oxidations leading to aromatization, and intramolecular cyclization with the exchange of N-regioselectivity. An attempted synthesis of regioisomeric natural product zanthochilone has been described in brief with reversal of reduction selectivity.