Ethyl pyrrole-3-glyoxalate

A special technique was necessary to obtain good yields of ethyl pyrrole-3-acetate from ethyl pyrrole-3-glyoxalate. Reduction over W-7 Raney Ni in 50% aq ethanol was accompanied by major ring reduction and tarring. By use of a two-phase system, toluene and 50% aq ethanol, these side reactions could be curtailed. Apparently the desired product was removed effectively from the aqueous layer into the toluene as soon as it was formed (26). 

Type (ii) cyclizations are more common. Thus, acid derivatives of pyrrolo[l,2-f>]-[l,2,5]benzothiadiazepine 5,5-dioxide 346 and 347 have been prepared from amino sulfonyl pyrrole 345 with acetal (2006JMC5840) or the semiacetal (1994JHC867) of ethyl glyoxalate or ethyl 2,2-diethoxy propionate (1996FES425) in the presence of PTSA catalyst in boiling absolute ethanol by a Pictet-Spengler type of reaction (Scheme 73). 

The l-ethyl-2,3-dimethylpyrrole whose nitrogen atom carries an ethyl group cannot be converted into a pyrrolenine form. Ozonolysis of this pyrrole derivative, however, not only yielded methylglyoxal (2.9%) but also dimethylglyoxal (8.6%). The ozonolysis of 1,2-dimethylpyrrole yielded glyoxal (5.1%) and methylglyoxal (8.3%). Here again, conversion of the pyrrole derivative in a pyrrolenine form is impossible. 

Pyrrole- and Furan-fused Thio diens and Related Compounds.— The interest in the chemistry of thienopyrroles is still increasing. Starting from 2-amino-3-carbonyl-substituted thiophens obtained by the Gewald reaction, the A -ethoxy-carbonylmethyl derivative (245) was prepared either by direct alkylation with ethyl bromoacetate, or by reductive alkylation with methyl glyoxalate. The compounds (245) were then ring-closed directly, or after acetylation, to the... 

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