Pyrroles alkoxy

As in carboxylic esters it is possible to substitute alkoxy groups of Fischer-type carbene complexes by non-carbon nucleophiles, such as other alcohols [73,214,218], enols [219], aliphatic amines [43,64,66,220-224], aniline [79], imines [225], or pyrroles [226]. Strong nucleophiles can also lead to a dealkylation of methoxy-substituted carbene complexes (5 2 at the methyl group, [227]), in the same way as methyl esters can be cleaved by nucleophiles such as iodide. Carbon... 

Better reagents than lithium aluminum hydride alone are its alkoxy derivatives, especially di- and triethoxyaluminohydrides prepared in situ from lithium aluminum hydride and ethanol in ethereal solutions. The best of all, lithium triethoxyaluminohydride, gave higher yields than its trimethoxy and tris(/er/-butoxy) analogs. When an equimolar quantity of this reagent was added to an ethereal solution of a tertiary amide derived from dimethylamine, diethylamine, W-methylaniline, piperidine, pyrrolidine, aziridine or pyrrole, and the mixture was allowed to react at 0° for 1-1.5 hours aldehydes were isolated in 46-92% yields [95,1107], The reaction proved unsuccessful for the preparation of crotonaldehyde and cinnamaldehyde from the corresponding dimethyl amides [95]. 

Complex benzofurans, such as N-substituted 3-oxo-l,3-dihy-drobenzofuro[2,3-c]pyrroles (95),263 or bacteriostatic substituted 5,6,7,8-tetrahydrobenzofuro[2,3-6]pyridines,270 4a-alkoxy-l,2,3,4,4a, 9b-hexahydrobenzofuro[3,2-c]pyridines and polysubstituted benzo-furo[3,2-c]pyridines,271 and other polyheterocyclic compounds with sulfur or nitrogen atoms272,273 have also been synthesized by this method. 

A third route to 3-vinylpyrrole complexes originates from 3-acyl-pyrrole complexes and readily provides access to alkoxy-substituted P-vinylpyrrole complexes. The carbonyl oxygen on these complexes is nucleophilic, and treatment of the 3-acetylpyrrole complex 38 with methyl triflate gives the methoxy-2-azafulvenium complex 143. Addition of DBU to 143 at low temperature results in deprotonation of the pendant methyl group on C-6 to give the methoxy-substituted P-vinylpyrrole complex 144 (Figure 26). 

In Table II the pK s of the 2- and 3-carboxylic acids of thiophene, furan, and pyrrole are reported. While pyrrole carboxylic acids, like the alkoxy- and amino-substituted benzoic acids, are weaker, thiophene- and furan carboxylic acids, like the chloro-and bromobenzoic acids, are stronger than unsubstituted benzoic acid. This behavior is confirmed by other side-chain reactivity data.41... 

J. 3-Alkoxy Pyrroles via Addition of Isocyanide (or Carbon Monoxide)... 

Methylsulfanyl)-l//-pyrrole-3-carbaldehydes 1407 were obtained in high yields using the same approach, starting from lithiated l,l,4-trialkoxy-2-butynes and isothiocyanates, followed by hydrolysis of the resulting 3-(dialkoxymethyl)-5-alkoxy-2-(methylsulfanyl)-l//-pyrtoles 1406 in acidic medium (Scheme 270) <2001CHE366, 2002RJ01070>. 

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