5,5 -Acyl bipyrroles

Porphycenes 51 bearing substituents at ethylenic carbons have been prepared from 5,5 -acyl bipyrroles 53 (05OL1887) (Scheme 26). However, oxidation of the intermediate annulene 54 is difficult, owing to the presence of the alkyl chains on the alkene bridges. These reduce conformational flexibility, resulting in a near-nonplanar geometry, which resists oxidation and/or aromatization (08CSR215). 

A diamine containing two directly connected pyrrolidine rings has been used as an additive in osmium tetroxide catalyzed dihydroxylations (Section D.4.4.). The synthesis from 2,2 -bipyrrole involves catalytic reduction, benzoylation, separation of the me so and dl forms by chromatography, amide hydrolysis, and resolution with tartaric acid26. The (S,S)-2,2 -bipyrrolidine thus obtained is then converted to the sterically hindered (. vV)-A,A -bis(3,3-dimcthylbutyl)-2,2 -bipyrrolidine [(S,S)-33] by acylation and reduction with lithium aluminum hydride27. 

Figure 5.12 Early proposal for the pathway to 4-methoxy-2,2 -bipyrrole-5-carboxaldehyde and schematic representation of the domain structures of the multienzyme RedL. KS, ketosynthase ACP, acyl carrier protein A, adenylation AT, acyltransferase, and ST, seryl transferase.

Sensitised photooxidation of tert-butyl 3-methoxypyrrole-2-carboxylate in methanol gives tert-butyl 3,5-dimethoxypyrrole-2-carboxylate together with a bipyrrolic oxidative coupling product (48). A novel ring cleavage of 4,5-bis(4-fluorophenyl)-a,a-bis(trifluoromethyl)-lH-pyrrole-2-methanamine (49) using 02( Ag) followed by acid catalysed dehydrocyclisation leads to the 4,4-bis(tri-fluoromethyl)imidazoline (50) which can be derivatised into (51), a compound which has acyl Co A cholesterol acyltransferase activity. 2-Imidazolidinethione... 

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