C decarboxylative

Five approaches to the synthesis of 5-amino-4-unsubstituted imidazoles (96) have been described and are summarized in Scheme 9. These are (a) reduction of 5-nitroimidazoles (97), (b) hydrolysis of carbamates and amides (98), (c) decarboxylation of imidazole carboxylic acids (99), (,d) ring transformations of 5-aminothiazoles (100), and (e) cyclisation of nitrile derivatives (101). 

Figure 5.8 Examples of formation and cleavage of carbon-carbon bonds (a) aldol condensation, (b) Claisen ester condensation and (c) decarboxylation of a P-keto acid. (From Voet and Voet, 2004. Reproduced with permission from John Wiley Sons., Inc.)...

Figure 1.6 Cis-pinonic acid Representative snapshots of MD trajectories taken shortly after the following reactions took place (a) H-transfer to CO group, (b) opening of the four-membered ring, and (c) decarboxylation. Reproduced with permission from Ref. [33]. Copyright 2013 American Chemical Society.

B-> C Decarboxylation after ester hydrolysis. C D Cyclisation to form a five membered... 

Cycloaddition of a-nitroso acrylic esters (749) to alkenes followed by base hydrolysis provides a route to 5,6-dihydro-4//-l,2-oxazine-3-carboxylic acids (750). These heterocycles on heating above 150 °C decarboxylate to furnish y-hydroxynitriles (thus the overall c/s-addition of OH and CH2CN to a double bond), which can be transformed further to y-lactones (751) by treatment with methanolic hydrochloric acid (Scheme 172) (79CC1090). The adducts were also reduced to a-amino esters (752) by the action of aluminum amalgam (Scheme 173) (79CC1089). 

R-COOH > R-H R-COOH R-H H- shorter-chain acids and hydrocarbons C Decarboxylation Cooper-Bray (6) degradation Irreversible... 

Figure 16 The putative KS-catalyzed decarboxylation of methylmalonyl-CoA. (a) In this proposed reaction, methylmalonyl-CoA bound to the ACP is decarboxylated by the KS domain to yield propionyl-ACP. The resulting propionate unit can then be transferred to the KS to initiate biosynthesis, (b) Decarboxylation of deuterium-labeled methylmalo-nyl-CoA in H20 would result in labeled propionyl-ACP. (c) Decarboxylation of unlabeled methylmalonyl-CoA in D2Q would result in labeled propionyl-ACP.

Published methods for decarboxylation of indole-2-carboxylic acid to form indole include pyrolysis or heating with copper-bronze powder, cop-per(I) chloride, copper chromite, copper acetate or copper(II) oxide, in for example, heat-transfer oils, glycerol, quinoline or 2-benzylpyridine. Decomposition of the product during lengthy thermolysis or purification affects the yields. From the perspective of green and sustainable chemistry, these methods have disadvantages associated with the choice of media and reagents as well as with the yields. Quite remarkably, however, in water at 255 °C, decarboxylation was quantitative within 20 min (Scheme 20) [77]. 

When the product of Step 1 was heated to between 180°C and 250 °C, decarboxylation occurred forming 2,6-dimethyl-hepta-1,5-diene as illustrated in Eq. 1 ... 

The reaction is carried out by passing an anhydrous mixture of the acid and an inert gaseous diluent through a heated tube at temperatures of 400-650 C. Decarboxylation appears to occur most readily when the acids are in vaporized form. 

What enzyme cofactor is associated with each of the following kinds of reactions (a) Transamination (b) Carboxylation of a ketone (c) Decarboxylation of an or-keto add... 

Bobrowski K, Schbneich C., Decarboxylation mechanism ofthe N-terminal glutamyl moiety in yglutamic acid and methionine containing peptides, Radiat. Phys. Chem., 1996,47,507-510. 

The structure 61 for precorrin-6A forced a complete change in the way the biosynthesis of vitamin B12 was viewed. This structure was full of surprises (a) the ring contraction step does not occur near the end of the pathway but has been completed at precorrin-6A 61 and is possibly carried out even earlier (b) oxidation has occurred prior to the formation of precorrin-6A and reduction is needed after it so the oxidation level along the pathway is not constant (c) decarboxylation of the C-12 acetate group is not an early step it occurs on the pathway beyond precorrin-6A (d) the 12a-methyl group of hydrogenobyrinic acid 60 is introduced initially at C-11 with subsequent migration to C-12. 

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