Pyrrole ring, intramolecular oxidative

Finally, the intramolecular coupling reaction between an olefin and a pyrrole ring has been examined (Scheme 40). In this example, a 66% isolated yield of the six-membered ring product was obtained. A vinyl sulfide moiety was used as the olefin participant and the nitrogen protected as the pivaloyl amide in order to minimize the competition between substrate and product oxidation. Unlike the furan cyclizations, the anodic oxidation of the pyrrole-based substrate led mainly to the desired aromatic product without the need for subsequent treatment with acid. 

Syntheses of this class of compounds usually involve 1,2,5-thiadiazepine ring 333 (Figure 6) which is stable in the S-oxidized form and structurally represents cyclic pyrrole N-sulfonyl derivatives. Most of the synthetic strategies include formation of an S-Npyrroie bond in the early stages. A final cyclization step typically includes (i) intramolecular cyclization by creation of an N-X bond from a suitable pyrrole precursor or (ii) a 6 + 1 type cyclization that involves dielectrophilic species to form linker X and utilizes the nucleophilicity of the phenyl amino group and of the pyrrole ring at C2. Intramolecular processes with the formation... 

The palladium catalysed substitution reaction of allylic systems has also been utilised in the formation of five membered rings. Intramolecular nucleophilic attack of the amide nitrogen atom on the allylpalladium complex formed in the oxidative addition of the allyl acetate moiety on the catalyst led to the formation of the five membered ring (3.63.). In the presence of a copper(II) salt the intermediate pyrroline derivative oxidized to pyrrole.80... 

Oxidation of the 1-aminoquinazolinones (44) with lead tetraacetate culminated in the intramolecular addition of the resulting N-nitrene intermediate to the triple bond to give the pyrrolo[2, l-b]quinazoline (45) [85CC544 86JCS(P1)1215]. The pyrrole ring of 47 was also formed by cyclization of 2-methyl-3-phenacylquinazolin-4-one (46) with dilute aqueous alkali followed by fusion (86T4481). 

Acyclic dialkylamines are not very reactive as nucleophiles in the oxidative alkylamination, however they are very prone to oxidation and, therefore, they are capable for unexpected behavior. Presumably, transformation 33 41 starts from oxidation of dialkylamme into imine 42, that is in equilibrium with enamine 43 (Scheme 28). The latter, as bifunctional C,W-nucleophile, attacks C-4 atom of the pyridazine ring to form cr -adduct 44, which then undergoes oxidative aromatiza-tion. Subsequent intramolecular oxidative amination of the intermediate 45 yields pyrrole derivative 41. The participation of imines in this process has been confirmed experimentally. In the presence of AgPy2Mn04, pyrimidopyridazine 33 reacts with authentic aldimines and ketimines 42 to give pyrroles 41. Transformation 33 41 represents not only a rare example of the tandem processes but... 

Although the 2,3,4,6-tetrahydro-l,l -methylene-2,2 -pyrromethen-5[l-//]-one (190) is not strictly a perhydropyrrolo[l,2-c]pyrimidine, it carries the essential features of this ring system. Synthesis was effected by treatment of pyrrole-2-carboxaldehyde (186) with diiodomethane in the presence of a base to give 187 which was oxidized to 188 by w-chloroper-benzoic acid. Intramolecular condensation of 188 gave 189 which was... 

More recently (2004), Joule proposed a novel synthetic route to access the akuammiline scaffold with reports from his group s synthetic efforts toward realizing this plan. Retrosynthetically, they envisioned akuammiline (1) to result from late stage imine formation of ketone 247 (Scheme 32). The functionality at position 16 would then be elaborated from a carbonyl contained in diketone 248, which in turn was planned to be obtained via an intramolecular Claisen condensation and double bond isomerization of enamine 249, the latter the product of an aza-Diels—Alder cycloaddition involving cyclic 1-aza-1,3-diene 250 and an acrylate 251. To access azadiene 250 they planned an oxidative ring opening of bicyclic pyrrole 252. 

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