2.4- Dimethylpyrrole-3,5-dicarboxylic

In the pyrrole series, ester groups a to nitrogen are more readily hydrolyzed by alkali, but those in a (3 position more readily by acid. Thus, in compounds such as diethyl 2,4-dimethylpyrrole-3,5-dicarboxylate (360) either ethoxycarbonyl group may be selectively hydrolyzed and, if desired, subsequently eliminated by decarboxylation. 

A mixture of DL-threonine and DL-allothreonine was prepared by the hydrogenation of ethyl diazoacetoacetate over paltinum oxide in 70% ethanol containing sulfuric acid (eq. 9.90). 2,4-Dimethylpyrrole-3,5-dicarboxylic acid diethyl ester was also obtained as a byproduct. 

SAFETY PROFILE Poison by inhalation and ingestion. A corrosive eye, skin, and mucous membrane irritant. Potentially explosive reaction with water evolves hydrogen chloride and phosphine, which then ignites. Explosive reaction with 2,6-dimethylpyridine N-oxide, dimethyl sulfoxide, ferrocene-1,1 -dicarboxylic acid, pyridine N-oxide (above 60°C), sodium -L heat. Violent reaction or ignition with BI3, carbon disulfide, 2,5-dimethyl pyrrole + dimethyl formamide, organic matter, zinc powder. Reacts with water or steam to produce heat and toxic and corrosive fumes. Incompatible with carbon disulfide, N,N-dimethyl-formamide, 2,5-dimethylpyrrole, 2,6-dimethylpyridine N-oxide, dimethylsulfoxide, ferrocene-1,1-dicarboxylic acid, water, zinc. When heated to decomposition it emits highly toxic fumes of Cl" and POx. 

In the full paper describing Woodward s sapphyrin-directed studies, it was noted that small amounts of sapphyrins could also be prepared via the HBr-catalyzed reaction between a bipyrrole dicarboxaldehyde and a dipyrrylmethane dicarboxylic acid. Additionally, the HBr-catalyzed reaction of 3,4-dimethylpyrrole 5.5 with 2,5-diformyl-3,4-dimethylpyrrole 5.3 was reported to afford small yields of decamethyl-sapphyrin 5.6 (Scheme 5.1.3). The fact that any sapphyrin could be isolated from these reactions, or even from the procedures of Schemes 5.1.1 and 5.1.2, attests to the stability of this pentapyrrolic macrocycle. 

PHOSPHORUS CHLORIDE (10025-87-3) Fumes in moist air. Contact with water, steam, or alcohols produces hydrochloric acid, phosphoric acid, and phosphine gas, which is pyrophoric, with possible ignition or explosion (may be a delayed reaction). Contact with air produces corrosive fumes. Violent reaction with carbon disulfide, 2,6-dimethylpyridine-iV-oxide, dimethyl sulfoxide, ferrocene l,l -dicarboxylic acid, pyridine, zinc powder. Reacts, possibly violently, with acids, alkali metals, alkalis, combustible materials, dimethyl for-mamide, organic matter, zinc powder. Incompatible with acetic anhydride, yV,V-dimethyl formamide, 2,5-dimethylpyrrole, sodium. Rapid corrosion of steel and most metals, except lead, occurs in the presence of moisture. 

Diethyl 2,6-dimethyl-3,5-pyridinedicarboxylate Diethyl 3,5-dimethylpyrrole-2,4-dicarboxylate... 

Pimethylpyrrole-2 4-dicarboxylic Acid (2 i-Dimethylpyrrole-Z 5 dicarboxylic acid). 

The synthesis begins with the preparation of Knorr s pyrrole (diethyl 3,5-dimethylpyrrole-2,4-dicarboxylate), which is made by the reaction of ethyl acetoacetate (ethyl 3-oxobutanoate) with ethyl 2-amino-3-oxobutanoate. The latter is made by nitrosation and subsequent reduction of ethyl acetoacetate. 

Diels-Alder addition product, from 1-methylpyrrole and maleic anhydride 2 is a further example of this sort of reaction. 2-Methylpyrrole behaves similarly, but the initial product (10) from pyrrole is obtained in small yield because it reacts further (p. 88). Pyrroles such as 2-methyl-, 1,2-dimethyl-and 2,4-dimethyl-pyrrole undergo similar Michael additions with methyl acetylenedicarboxylate s, 254 jn the third instance two molecules of the pyrrole reacting to form (11). 1-Methoxycarbonylpyrrole reacts at the 2-position with acetylene dicarboxylic acid254 as well as giving a Diels-Alder type of product (p. 82). With the same acid, ethyl 3,5-dimethylpyrrole-2-carboxylate undergoes Michael addition at the vacant jS-position giving (12). Other examples of reactions with dienophiles are discussed below... 

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