Heterocyclics thieno pyrroles

Another nonclassical heterocycle, thieno[3,4-cJpyrazole, was synthesized,109 utilizing the ability of mesoionic ring systems to act as 1,3 dipoles in cycloadditions.106 Condensation of JV-phenylsydnone (162) with dibenzoylacetylene formed 3,4-dibenzoyl-l-phenylpyrazole (163) (85%) with phosphorus pentasulfide in refluxing pyridine, this gave 85% of 2,4,6-triphenylthieno[3,4-c]pyrazole (164) [Eq. (44)]. The synthesis of 5-methyl-1,3,4,6-tetraphenylthieno[3,4-c]pyrrole is also described.107... 

Generally, cycloadditions represent powerful reactions for construction of heterocycles. Tandem intramolecular Diels-Alder/retro-Diels-Alder reaction sequences were applied in the syntheses of many A,B-diheteropentalenes <1996GHEC-II(7)1>. Gribble and co-workers <1998SL1061> reported new syntheses of pyrrolo[3,4-, ]indoles 426, benzo[4,5]furo[2,3-f]pyrroles 429, and benzo[4,5]thieno[2,3-4pyrroles 430 using the 1,3-dipolar cycloaddition... 

Recently, the synthesis of 5-aryl-2-oxopyrrole derivative 210 as synthon for the highly substituted pyrrole 211 as starting compound for fused heterocycle 212 was published [56], Diethyl 6-bcnzyl-5-phenyl-6//-thieno[2,3-/ ]pyrrolc-2,4-dicarboxylatc 212 was prepared from ethyl l-benzyl-5-chloro-4-formyl-2-phcnyl-l //-pyrrolc-3-carboxylate 211 and ethyl 2-sulfanylacetate in refluxing ethanol (Scheme 41). 

Ando et al. <92CC1100,95T129) have used 3,5-dihydro- l/f-thieno[3,4-c]pyrrole-2,2-dioxides (214) with a variety of A-substituents as useful synthetic building blocks for the preparation of polycyclic heterocycles which are inaccessible by other methods. These cycloadditions were performed with electron-deficient dienes (e.g., DMAD) under thermal conditions in a sealed tube. Cycloaddition takes place but the S02 is extruded only after the pyrrole ring has undergone cycloaddition with the dienophile. 

Gribble GW, Pelkey ET et al (1998) New syntheses of pyrrolo[3,4-b]indoles, benzo[b]furo [2,3-c]pyrroles, and benzo[b]thieno[2,3-c]pyrroles. Utilizing the reaction of muenchnones (l,3-oxazolium-5-olates) with nitro heterocycles. Synlett 1061-1062... 

Hu S, Huang Y, Poss MA, Gentles RG (2005) A novel route to the 5,6-dihydio-4H-thieno[3,2-b]pyrrol-5-one ring system involving an intermediate substituted-thiophene synthesis. J Heterocyclic Chem 42 661-667... 

Non-classical Thienofliiophens and Related Systems.—Phosphorus pentasulphide treatment of suitable vicinal dibenzoyl heterocycles has been established as a convenient pathway to tetraphenylthieno[3,4-c]thiophen, 5-methyl-1,3,4,6-tetraphenylthieno[3,4-c]pyrrole, and hexaphenylthieno[3,4-/]isothionaphthene, and their cycloaddition reactions have been studied. Further details on thieno-[3,4-c]pyrazole, thieno[3,4-c]furan, and thieno[3,4-c]pyrrole have appeared (see Volume 3, p. 449). 

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