Indoles having an ester functionality in the 3-position were prepared from 2-(2-nitrophenyl)propenoic acid derivatives via a palladium-catalyzed reductive N-heteroannulation using carbon monoxide as the ultimate reducing agent. The starting materials were prepared either by a Stille coupling of 2-halo-1-nitrobenzenes with ethyl 2-(tributylstannyl)-2-propenoate or by vicarious nucleophilic substitution of nitrobenzenes followed by a Knoevenageltype condensation with an aldehyde. Synthesis of an example of a 3-nitrile-and a 3-sulfone-substituted indole is also described using the same type of methodologies.

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A flexible route to both symmetrical and unsymmetrical 1H,8H-pyrrolo­[3,2-g]­indole has been developed. The key and ultimate step is a double palladium-catalyzed, carbon monoxide mediated reductive cyclization of 1,4-dialkenyl-2,3-dinitrobenzenes. The cyclization precursors were prepared by a double Kosugi–Migita–Stille cross coupling of 1,4-dibromo-2,3-dinitrobenzene with an alkenyltin reagent to give symmetrical products. Unsymetrical cyclization precursors were prepared by two sequential cross couplings using 4-iodo-2,3-dinitrophenyl trifluoromethanesulfonate as the starting material.

A Base-Modulated Chemoselective Synthesis of 3-Cyanoindoles or 4-Cyanoquinolines Using a Palladium-Catalyzed N-Heterocyclization. -Depending on the absence or presence of DBU, cyanoalkenes (I) cyclize either to indole or quinoline derivatives (II) or (III). CO is employed as reducing agent. Alkenes bearing no nitrile moiety also afford the corresponding indoles under conditions A). Treatment of these alkenes under conditions B) or C) gives different results depending on the alkene substituent. -(BANINI, S. R.; TURNER, M. R.; CUMMINGS, M. M.; SOEDERBERG*, B. C. G.; Tetrahedron 67 (2011) 20, 3603-3611, http://dx.

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