Dehydration-decarboxylation

D-Mevalonic acid is the fundamental intermediate in the biosynthesis of the terpenoids and steroids, together classed as poly-isoprenoids. The biogenetic isoprene unit is isopentenyl pyrophosphate which arises by enzymic decarboxylation-dehydration of mevalonic acid pyrophosphate. D-Mevalonic acid is almost quantitatively incorporated into cholesterol synthesized by rat liver homogenates. 

At the other end of the reaction, deviations from idealized rate laws are attributed to secondary reactions such as degradations of acids, alcohols, and amines through decarboxylation, dehydration, and deamination, respectively. The step-growth polymers which have been most widely studied are simple... 

Together with the decarboxylation, dehydration of PPA takes place on heating. Examination of the decarboxylation of copolymers of acrylic and propynoic adds having blocks in their structure has revealed two interesting phenomena261 262. ... 

What may be characterized as an aza-Tr-allylpalladium complex has been proposed as an intermediate in the preparation of a, -unsaturated nitriles by decarboxylation-dehydration of allyl a-cyanocarboxy-lates (equation 144).369 These reactions have been summarized in the context of several reviews.89,117 If the oxa-7r-allyl species is blocked from the elimination of a (3-H, then it can undergo typical ir-allylpalla-dium chemistry, such as insertion by alkenes, dienes and CO (equation 145).370 371... 

The analysis depicted for (64) reveals that the synthesis of benzofuran involves the conversion of salicylaldehyde into the corresponding aryloxyacetic acid by reaction with sodium chloroacetate in the presence of alkali, followed by heating with a mixture of acetic anhydride, acetic acid and sodium acetate (Expt 8.24). The ensuing cyclisation may be regarded as an internal Perkin reaction (Section 6.12.3, p. 1036) accompanied by a decarboxylative dehydration step. 

After two minor dust explosions in an industrial adipic acid dryer, evidence was obtained that adipic acid forms an iron complex capable of both decarboxylation/ dehydration of adipic acid to cyclopentanone and of catalysing air oxidation, giving exotherms from as low as 135°C. 

Decarboxylative dehydration of -hydroxy carboxylic acids (9, 504). Study of the stereochemistry of this reaction indicates that syn-P-hydroxy carboxylic acids are usually converted into (E)-alkenes (equation I), in contrast, the anti-isomers are converted... 

DECARBOXYLATIVE DEHYDRATION N,N-Dimethylformamide dineopentyl acetal. Triphenylphosphine-Diethyl azodicar-boxylate. 

Decarboxylative dehydration of 3-hydroxycarboxylic acids, f/ireo-S-Hydroxy-carboxylic acids (1) undergo lactones derived from 1. ... 

DECARBOXYLATIVE DEHYDRATION Triphenylphosphine-Dielhyl azodi-carboxylate. 

Decarboxylation-dehydration. Marshall and Faublllc achieved the synthesis of bicyclo[3.3.1]-A -nonene (3), the most flagrant known violator of the Bredt rule, via the mesyloxy-acid (I). When this acid was treated with dimsylsodium in dimethyl... 

Fatty acids have predominantly even numbers of carbon atoms because they are effectively formed from acetyl (C2) units, which are derived from glucose in the presence of various enzymes, coenzymes and carrier proteins. An overall scheme for saturated fatty acid biosynthesis is presented in Fig. 2.13, in which it can be seen that the first step is the formation of acetyl coenzyme A (often abbreviated to acetyl-CoA). One molecule ofacetyl-CoA undergoes addition of CO, to form malonyl-CoA, while the acetyl group on another molecule is transferred to an enzyme (fatty acid synthase). The malonyl unit (C3) is added to the enzyme-bound acetyl unit, which produces a butyryl group following loss of C02, dehydration and reduction. Six further steps of combined malonyl addition, decarboxylation, dehydration and reduction occur to yield palmitate (C16). Higher acids are built from palmitate in a similar... 

Figure 10 Proposed mechanism for decarboxylative dehydration of arogenate (41) to Phe (1) by ADT. B, base.

Decarboxylative dehydration 5-Hydroxy-/J,7-unsaturated cyclohexenecar-boxylic acids (1) when treated with this acetal of DMF at room temperature or somewhat higher are converted into 1,3-cyclohexadienes (2) in high yield coproducts are DMF and neopentyl alcohol. a-Methylnaphthalene (b.p. 80°/0.05... 

Alkenes. j3-Hydroxy carboxylic acids are converted into alkenes in fair to good yield by treatment with triphenylphosphlne and diethyl azodicarboxylate (equation I). The reaction involves loss of CO2 and HaO (decarboxylative dehydration). 

The biosynthesis begins with acetyl CoA which is combined with a second unit of acetyl CoA to give acetoacetyl CoA. A third acetyl CoA molecule is then added and the 6 C body so produced is hydrogenated to mevalonic acid by means of NADPH -I- H+ with the liberation of coenzyme A. Mevalonic acid, which was discovered as a growth factor for microorganisms, is an important intermediate. The active isoprene, iso-pentenyl pyrophosphate, is derived from it by decarboxylation, dehydration, and phosphorylation with ATP. 

Depending on the basic mechanism of the template process, secondary reactions can take place. For instance, in polycondensation, there are such well-known reactions as cyclization, decarboxylation, dehydration, oxydation, and hydrolysis. 

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