2,3 -Bipyrroles

Structural and physical studies of the two other C-C linked bipyrroles 5 and 6, have been restricted to theoretical calculations these suggest that the s -trans planar conformations are the most stable [83JST(104)197 85JST( 124)307 88JCC369], 

---

An example of dimerization involving a-protonation is provided by the formation of the 2,2 -bipyrrole (44) on treatment of 3,4-dimethylpyrrole with 6N HCl (68JCS(C)2527). The... 

The reaction of 2,2 -bipyrrole with orthoformic acid triethyl ester in the presence of phosphoryl chloride (POCI3) produced a compound which gave the H NMR spectrum 5. Which compound has been prepared ... 

This rational approach for the synthesis of isocorroles is complemented by observations discovered in investigations on porphycencs. Firstly as minor side products of the McMurry coupling of 2,2 -bipyrroles-5,5 -dicarbaldehydes, e.g. 3, isocorroles arc formed, e.g. 5.2... 

Two type la syntheses of (3-hydroxypyrroles have appeared. An aza-Nazarov cyclization of l-azapenta-l,4-dien-3-ones produced (3-hydroxypyrroles including 2,2 -bipyrroles <06EJO5339>. A second approach to a (3-hydroxypyrrole involved an intramolecular N-H insertion into a rhodium carbene derived from the decomposition of a diazoketone <06JOC5560>. On the other hand, the photochemical decomposition of the diazoketone led to pyrrolidin-2-ones. 

There is a case where the resnlts of the electrode and chemical oxidation coincide (see Scheme 2.20). Calix[8]pyrrole was prepared from 3,3, 4,4 -tetraethyl-2,2 -bipyrrole during oxidative electrolysis in dichloromethane nsing platinum anode, tetrabutylammonium hydrogen sulfate as the... 

Jiao, L. Smith, K. M. A New Synthetic Route to 2,2 -Bipyrroles. Proceedings of the 233rd American Chemical Society National Meeting, Ghicago, IE, March 25-29, 2007. 

A closer inspection of A. luteoviolaceus by different groups provided a further variety of highly active metabolites, tetrabromopyrrole, hexabromo-2,2 -bipyrrole, tetrabromobiphenol, several simple phenols including 4-hydroxy-benzaldehyde and n-propyl-4-hydroxybenzoate, violacein (5) and related pigments, and the extremely strong siderophore alterobactin [97]. 

J -Bipyrroles. Oxidation of 1-aroylpyrroles (I) with Pd(OAc)2 in HOAc results in l,l -diaroyl-2,2 -bipyrroles (2), which are hydrolyzed by acidic aqueous methanol to 2,2 -bipyrroles (3). 

Aroylpyrroles dimerize on treatment with palladium(II) salts thus, oxidation of 1-benzoylpyrrole (168) with palladium acetate in acetic acid gives the 2,2 -bipyrrole (169). The ring-closed compound (170) is formed as a by-product (81CC254). 

The Lewis acid-catalyzed reaction of the endoperoxide of 1-methoxycarbonylpyrrole with enol ethers presents an interesting route to 2-alkylpyrroles (Scheme 30) (79TL3477, 80H(14)102>. In the case of the reaction with l-(trimethylsilyloxy)buta-l,3-diene, the reaction provides a viable route to indole, which, with only slight modification, can also be employed in the synthesis of 4-substituted indoles <8lH(l6)959>. The endoperoxide reacts with 1-methylpyrrole to produce the l,l -disubstituted 2,2 -bipyrrole in low yield. 

Finally, a coupled and decoupled 13C NMR spectrum of 2,2 -bipyrrole (Fig. 4.14(a,b) and an inversion-recovery series of 2,2 -bi pyridine (Fig. 4.15 [73 i]) illustrate signal assignments of heteroaromatic compounds by means of carbon-proton couplings and spin-lattice relaxation times. These spectra also exemplify the characteristic shift differences between n-excessive (2,2 -bipyrrole) and n-deficient heteroaromatic compounds (2,2 -bipyridine). 

Stanley AE, Walton LJ, Zerikly MK, Corre C, Challis GL (2006) Elucidation of the Streptomyces coelicolor Pathway to 4-Methoxy-2,2 -bipyrrole-5-carboxaldehyde, An Intermediate in Prodiginine Biosynthesis. Chem Commun 3981... 

One of the widely studied, stable constitutional porphyrin isomers encompassing 18jt-electrons in a cyclic conjugated pathway is porphycene 38 (Scheme 17). Other isomers such as NCPs are much less stable and are not discussed here. Porphycenes consist of two 2,2 -bipyrrole subunits linked by two double bonds and are thus named as [18] porphyrin( 2.0.2.0). ... 

Nonell and coworkers (01JPP846) have also reported a non-decarboxylative procedure based on 2,2 -bipyrrole derivative 39 (Scheme 18), bearing two sets of orthogonal esters. The tetraester 39 could readily be transformed to dialdehyde 36 (R=C6H5) through the intermediacy of 40 by use of the MacFadyen-Stevens sequence (1962JA635) even as the direct conversion of 40 to 36 (R =C6H5) was not facile. 

Alternatively, the conversion of tetraester 39 (R1=Et) to 2,2 -bipyrrole derivative 36 through 41 was achieved (1993JOC2340) by treating 39 with NaOH/ethylene glycol at reflux (Scheme 19). 

Sanchez-Garcia (09OL77) has reported a one-pot procedure (Scheme 21) for the synthesis of 4,4 -diaryl-4,4 -diheteroaryl-substituted-2,2 -bipyrrole 45 based on the oxidative coupling of 2-trimethylstannylated pyrrole 44. 

The general synthetic approaches for expanded porphycenes rely upon the insertion of alkylidene or alkylidyne moieties either as the meso-bridge or between the 2 and 2 positions of the bipyrrole subunits. Thus, the vinylogous dialdehyde 72 (Scheme 35) obtained from 4,4 -dipropyl-2,2 -bipyrrole with 3-(dimethyl-l-amino)acrolein has been converted to (1993PAC143) to 73 using a standard McMurry-type coupling. Expanded porphycene 73 with TFA precipitates as dication 74. 

---