Pyrrolo indol-3 -ones

Indolo[3,2-fl]pyrrolo[3,4-c]carbazoles 120 have been obtained in one step from indole and the corresponding maleimides in acetic acid, with coformation of the Michael adducts 121 (Scheme 15). This reactitai required careful temperature control in order to obtain the desired product ratios. An alternative independent synthesis of compounds 120 could also be accompKshed from 2,3 -biindolyl (115) andsuitable maleimides in hot acetic acid (99T2363). The system 120 where R = H has also been reported as a minor product during studies toward a synthesis of the alkaloid arcyriaflavin A (95TL2689). 

Additional communications deal with the synthesis of pyrrolo[l,2-cjquinazolines by treatment of methyl 3-alkyl-l,3-dihydro-2-oxo-3-(triphenylphosphoranylidenamino)-2//-indole-l-carboxylates (275) with ketones to afford A -pyrrolin-4-ones (276). As Scheme 100 shows, 276 can... 

Suitable amide derivatives of pyrrole- and indole-2-caroxylic acids 13 result in good yields of 5,6-dihydrobenzo[c]pyrrolo[3,2-e]azepin-4(3F7)-one 14a and its indole analog 14c (Equation (2) (2005TL8177)). 

X-Ray crystallographic analysis was used to investigate the mechanism by which the cyclic azimine 17 was converted into pyrrolo[3,2- ]indole 18 <1996CC945>. Isolation and X-ray analysis of different photolabile intermediates revealed one of them to be the fused triazoline 19 as shown in Scheme 1. 

Pyrrolo[l, 2-a]imidazoI-2(3 ff)-ones synthesis, 6, 1001 Pyrrolo[3,2-6]indoles synthesis, 4, 243 Pyrrolo[3,2-/]indolizines synthesis, 4, 274, 296 Pyrroloisoquinolines synthesis, 4, 513... 

Fischer indole cyclization and transformation of a nitrile to an ester (Pinner synthesis) to yield diethyl 5-hydroxy-1 T/-pyrrolo[2,3-/]quinoline-2,7-dicarboxylate (183) was performed in one step by... 

Tr-Density calculations for l//,5//-pyrrolo[2,3-/Iindole (8.164) and 3//,6//-pyrrolo 3,2-c]indole (8.165) indicate 3,7- and 1,8-substitution, respectively, as found in acylation and diazonium coupling (83CHE871). MO calculations indicate that the 1- and 3-positions are the most reactive ones in 4//-pyrrolo[ 1,2-u]benzimidazole (8.166) (74CHE230). The same result is more easily deduced and understood as follows. Although the lone pair on N-4 can be delocalized to the 1-, 3-, 5-, or 7-positions, the important factor is delocalization of the lone pair from N-9 to the 1- and 3-positions (e.g., as in 8.167). Although the 6tt pyrrole ring of the ground... 

A tandem carbonylation-cyclization radical process in heteroaromatic systems bearing electron-attracting substituents such as l-(2-iodoethyl)indoles and pyrroles 970 result in the formation of 2,3-dihydto-l//-pyrrolo[l,2- ]indol-1-ones and 2,3-dihydro-l//-pyrrolizin-l-ones 974 (Scheme 188). The AIBN-induced radical reaction of compounds 970 with Bu3SnH under pressure of CO suggests that the acyl radical 972, derived from radical 971 and CO, would undergo intramolecular addition to C-2 of heteroaromatic system, and the benzylic radical 973 so obtained, upon in situ oxidation would produce final product 974 <1999TL7153>. 

When a benzene solution of 1 -(2-iodoethyl)indole 975 was heated at 80 °C with 1.2 equiv of Bu3SnH and 0.2 equiv of AIBN under 80 atm of carbon monoxide for 3 h, most of the starting material was recovered and low yields of cyclization and reduction products 976, 977, and 978 were isolated (Equation 230) <1996AGE1050>. Addition of tin hydride in three small portions (0.4 equiv each time) at 1 h intervals allowed minimization of the reduction product 977 and almost completely transformed starting material into 2,3-dihydro-177-pyrrolo[l,2- 7]indol-l-ones 976 <1999TL7153>. When T(2-iodoethyl)-l/7-pyrrole-2-carbaldehyde was subjected to the optimum conditions, l-oxo-2,3-dihydro-l//-pyrrolizine-5-carbaldehyde 979 was isolated in a 30% yield (Equation 231). 

The reduction of the pyrrolo[3,4-A]indol-3(2//)-ones 462 with LAH in toluene at reflux temperatures gave the expected 1,2,3,4-tetrahydro derivative 463 in 45% yield. However, the dihydropyrrolo[3,4-6]indole 464 was also isolated. The yield of this latter product was increased from 27 to 42% when the reduction was carried out in the presence of l-ethylpiperidine. This was interpreted as increasing the propensity toward C-1 proton extraction from the aluminum-oxygen complex 465. 

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