Fused pyrrole

It is of interest to compare the stability of the protonated forms of benzo[u], benzo[Z>] and benzo[c] fused pyrroles, i.e. the cations derived from indolizines, indoles and isoindoles. Indolizine gives a stable pyridinium ion and does not polymerize in the presence of acid. 

Pyrrolo[l,2-fl]thieno[2,3-c]pyrazine (186) brominated mainly in the fused pyrrole ring. Only the third bromine atom introduced substituted the thiophene /3-position (86JHC17). 

The bis[l,2]dithiolo[5,4- ][5, 4 -< ][l,4]thiazine ring systems of Rees and co-workers easily extrude sulfur from the thiazine ring and undergo contraction to the fused pyrrole derivatives <1997CC879>. These tricycles generally have a nonplanar, scorpion-like solid-state structure <1998JOC2189> however, the dicarbonyl product of... 

Intramolecular nucleophilic additions by nitrogen functional groups onto pendant alkynes and allenes represent an important class of type la approaches to functionalized pyrroles. A platinum-catalyzed (PtCl4) cyclization of homopropargyl azides provided an entry to 2,5-disubstituted pyrroles and 4,5,6,7-tetrahydroindoles (fused pyrroles) <06OL5349>. 

A novel intramolecular photocycloaddition involving vinylogous amides and allenes led to an interesting type lb entry to functionalized pyrroles <060L4031>. For example, photolysis of allene 11 provided fused pyrrole 12 via a [2+2] cycloaddition and retro-Mannich reaction. 

Following the communcation in 2004, a full report appeared that described type Ilac cyclocondensation reactions between dihydroisoquinolines and a-nitrocinnamates leading to complex fused pyrroles <06JOC9440>. The latter were converted into the lamellarin alkaloids and related analogues. 

Azomethine ylide cycloadditions have been utilized to prepare a number of novel fused pyrroles including pyrrolo[2,1 -a isoquinolincs <06CHJC279, 06TL1469> and pyrrolo[l,2-Zdpyridazines <06SL804>. Fused hydroxypyrroles were obtained in cycloaddition reactions with trimethylsilylketenes (TMS ketene) <06TL1469>. 

Cycloaddition reactions involving dithione intermediates derived by the reductive extrusion of sulfur atoms from [1,2,3,4,51pen tathi enopino[6,7-i>]pyrroles provided access to 1,4-dithin-fused pyrroles (i.e., 89) <06OL4529>. 

Efficient synthesis of highly substituted alkylpyrroles and fused pyrroles has been achieved by three-component coupling of ... 

Similarly, in a 1,3-dipolar cycloaddition of DMAD to the conformationally locked cyclic a-alkoxycarbonylnitrone (727), bicyclic ring systems, containing a nitrogen atom at the bridgehead position have been synthesized. A mechanistic interpretation of the origin of the fused pyrroles (729) includes the intermediate formation of the aziridine ring in (728) (Scheme 2.303) (820). 

Ohta has developed a facile and efficient synthesis of pyrroles 42 that involves the Pd-catalyzed oxidative cyclization of hydroxy enamines such as 41 [41]. Fused pyrroles 43 and 44 were also synthesized in similar fashion. 

Using a similar Larock strategy, Gronowitz has synthesized a series of thienopyrroles, such as 193, and other heterocyclic-fused pyrroles [131, 132], Related reactions leading to indoles will be presented in the next chapter. 

Current work is focused on the benzoheteropines with the fused pyrrole (or indole), thiophene or furan rings, i.e., ortho-fused 6 + 7 + 5 ring systems with carbons only on the six-membered ring, one heteroatom on the five-membered ring and one or more heteroatoms on the seven-membered ring. The variety of heteroatoms is limited to nitrogen, oxygen and sulfur. Several examples of the related cyclic systems with the other heteroatom distribution or peri-fusion are briefly summarized in Section 4.3. The current first specialized review covers synthetic, reactivity and structural aspects reported from the late 1989 until 2007. 

Benzoheteropines with Fused Pyrrole, Furan and Thiophene Rings... 

Two major types of transformations are usually used for the synthesis of benzazepines with the fused pyrrole and indole rings. Construction of the... 

Lactonization of the suitable hydroxy acids or their derivatives is the most common synthetic method for benzoxepinenones with fused pyrrole rings. Therefore, reduction of the formyl group in the ester aldehyde 121 with sodium borohydride gives a mixture of alcohol 122 (80% yield) and lactone 123 (19%). Further heating of the open-chain product 122 in refluxing ethanol affords cyclic lactone 123 quantitatively (Scheme 25 (1998T11079)). 

Annulation of the pyrrole ring. o-Aminoketone 179, bearing the protected aldehyde moiety, can be smoothly reacted with substituted phenyl alanines and transformed into 1,4-benzodiazepinones 180 with a fused pyrrole ring (Scheme 36 (1992BMCL1639)). 

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