2,2 -bipyrrolyl

Itahara has also found that the phenylation of A-aroylpyrroles can be achieved using Pd(OAc>2 [30, 31]. Although A-benzoylpyrrole (22) yields a mixture of diphenylpyrrole 23, cyclized pyrrole 24, and bipyrrolyl 25 as shown, l-(2,6-dichlorobenzoyl)pyrrole 26 gives the diphenylated pyrrole 27 in excellent yield. The IV-aroyl groups are readily cleaved with aqueous alkali and the arylation reaction also proceeds with p-xylene and p-dichlorobenzene. Unfortunately, N-methyl-, iV-acetyl-, and A-(phenoxycarbonyl)pyrroles give complex mixtures of products. 

Macrocyclic molecules that have the ability to bind anions continue to attract considerable synthetic effort. During the course of such studies, it has been found that hybrid calixpyrroles in which some pyrrole units are replaced by thiophenes are good receptors for Y-shaped anions such as carboxylates <2005JOC1511>. One such macrocyle is compound 176. The synthesis of this compound utilizes the same type of chemistry as has been adopted for the thiaporphyrins. The bis(bipyrrolyl)furan 174 was reacted with the diol 175 (1.1 molar ratio) in MeCN in the presence of a catalytic amount of Bp3-Et20 at 0°C to give 176 in 44% yield. 

Reactions of Pyrroles. 1,3-Di-t-butylpyrrole forms the first stable protonated pyrrole, the salt (104). Electrophilic substitution of pyrrole with MeaC or Me FC in the gas phase occurs mainly at the j3-position, as does nitration and Friedel-Crafts acylation of l-phenylsulphonylpyrrole2 Pyrrole-2,5-dialdehyde has been prepared by Vilsmeier-Haack formylation of the ester (105), followed by hydrolysis. A similar method has been used to convert the di-acetal (106) into pyrrole-2,3,5-tricarbaldehyde. AT-Benzoyl-pyrrole reacts with benzene in the presence of palladium(II) acetate to yield a mixture of l-benzoyl-2,5-diphenylpyrrole, the bipyrrolyl (107), and compound (108). Treating lithiated A-methylpyrrole with nickel(II) chloride results in the polypyrrolyls (109 = 0-4). 2-Aryl-1-methylpyrroles are obtained by cross-coupling of l-methylpyrrol-2-ylmagnesium bromide with aryl halides in the presence of palladium(0)-phosphine complexes. ... 

Typical examples of this type include the cleavage reactions of octaphenyl-l,l -bipyrrolyl and of hexaphenyl-l,l -biimidazolyl, which on exposure to light yield the colored free radicals 49 and 50, respectively. These reactions form the basis of a photochromic system. Photochromism is observed both in the crystalline state and in solution. 

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