Ethyl 5- -3,4-diethylpyrrole-2-carboxylate

The reader is referred to the synthesis of ethyl 3,4-diethylpyrrole-2-carboxylate published in Organic Syntheses. 

Pyrrole synthesis. A new route to pyrroles1,2 is based on a base-catalyzed Michael addition of an alkyl isocyanoacetate to a nitroalkene to give an intermediate that cyclizes to a pyrrole. The nitroalkene is generally obtained from a P-acetoxy nitroalkane (1), prepared by a nitro aldol reaction of an aldehyde with a nitroalkane. The synthesis of ethyl 3,4-diethylpyrrole-2-carboxylate (2) is typical. 

Two equivalents of OBU are used here. One equivalent of DBU eliminates acetate from one of the reactants to form 3-nitro-3-hexene in situ, which goes on to form the pyrrole. The intermediate ethyl 3,4-diethylpyrrole-2-carboxylate can also be... 

Ethyl 3,4-diethylpyrrole-2-carboxylate 1 H-Pyrrole-2-carboxylic acid,... 

Alternatively, the ethyl 3,4-diethylpyrrole-2-carboxylate may be carried on directly to give octaethylporphyrin,5 although the yields reported (ca. 40%) are not quite as good as those obtained by the present procedure. Similarly, this substance or the 3,4-diethylpyrrole produced by the present procedure could conceivably serve as the basis for an an improved synthesis via a Mannich base-type approach such as that outlined in refs. 9 12. 

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