Olefinic amides, dehydration

For further dehydration, for example, of aldoximes and amides to nitriles, of alcohols to olefines, as well as the synthesis of heterocycles like oxiranes and aziridines see Section 18.5. 

In general, dehydration means loss of water molecules from chemical substances, irrespective of their structure. Even if all cases where water is bonded in hydrate form are excluded, a number of reactions remain which also include formation of nitriles from amides, lactones from hydroxy acids etc. However, the present treatment will concentrate on the heterogeneous catalytic decomposition of alcohols in the vapour phase, which can be either olefin-forming or ether-forming reactions, and on the related dehydration of ethers to olefins. 

In a recent report, Padwa [64] disclosed a general method of wide applicability for constructing a variety of heterocyclic systems. It involved an amino furan ester as a more reactive four carbon component vis avis a pyrone in intramolecular Diels-Alder addition to an unactivated olefin. This method as applied to the synthesis of anhydrolycorinone consisted of the preparation of the tertiary amide 240 (Scheme 40) and its subsequent thermolysis to the N-o-bromoaroylindoline 241. It is believed that the initially formed cycloadduct 242 opened to the acyl iminium oxyanion 243, which by prototropy and dehydration generated 241. The latter, on photolysis in the presence of bis (tri-n-butyltin), furnished the tetracyclic ester 244, which was hydrolysed and decafboxylated to anhydrolycorinone as in the previous synthesis. 

The latter, on reaction with methylamine yielded via the P-epoxide 373, the trans-a aminoalcohol 374, which was N-acylated to the amide 375. Acid-catalysed dehydration of the tertiary alcohol 375, led to the olefin 375, from which the key radical precursor, the chlorothioether377 was secured in quantitative yield by reaction with N-chlorosuccinimide. In keeping with the earlier results recorded for structurally related compounds, 377 on heating in the presence of ruthenium dichloride and triphenylphosphine also underwent a 5-exo radical addition to generate the cyclohexyl radical 378 which recaptured the chlorine atom to furnish the a-chloro-c/5-hydroindolone 379. Oxidation of thioether 379 gave the corresponding sulfoxide 380, which on successive treatment with trifluoroacetic anhydride and aqueous bicarbonate led to the chloro-a-ketoamide 381. The olefin 382 resulting from base induced dehydrochlorination of 381, was reduced to the hydroxy-amine 383, which was obtained as the sole diastereoisomer... 

Unsaturated nitriles prepared by the dehydration of amides include 1-cyano-1-alkynes, e.g. 1-cyano-l-heptyne (85%), and 1-cyano-l-alkenes, e.g. /3-isopropylacrylonitrile (80%). Some dehydrating agents such as phosphorus pentachloride may lead to the formation of halogen-containing products phosphorus pentoxide is preferred in these cases. In a comparison of methods for preparing olefinic nitriles, it has been shown that... 

On the other hand, the primary thermal decomposition of polyamides of aliphatic-diamine and aromatic-dicarboxylic acid proceeded via the cis elimination process with formation of the products containing amide and olefin end groups. Nitrile end groups also proved to be formed by dehydration of the anfide groups formed in the primary process. 

Hydroformylation (0x0 reaction) affords aldehyde and an amide is added to the aldehyde under these reaction conditions to produce an acylamino acid as shown in eq. (17.32). This reaction is named the Wakamatsu reaction in which an amino acid is produced directly from an olefin [46,77]. Cobalthydrocarbonyl (HCo(CO)4) is a strong acid as the aldehyde reacts with amide to afford an aminoalcohol, and a dehydration condensation with HCo(CO)4 forms a carbon-Co bond, and carbonylation and hydrolysis to produce the acylamino acid [46,77]. The carbonylation... 

Due to their synthetic utility and pharmaceutical applications, a number of synthetic routes to a,P-unsatuiated nitriles have been developed. Classical methods include dehydration of amides [15] or aldoximes [16], Wittig- [17] and Peterson-type [18, 19] olefination processes, ammoxidation of alkenes [20], and carbocyanation of alkynes [21], These approaches suffer variously from high waste generation, low yields and poor stereoselectivity. As such the transition metal-catalysed cyanation of vinyl halides is an attractive route for the synthesis of alkaiyl nitriles. Whilst several instances of such transformations have been reported in the literature, the area remains underdeveloped, particularly in comparison to analagous cyanations of aryl halides. 

Certain secondary and tertiary alcohols are dehydrated to olefins, under the influence of H2SO4. These can then polymerize to give polymers insoluble in concentrated sulfuric acid. In spite of this, such compounds are classified into groups 6 or 7. In homologous series of monofunctional compounds (ethers, esters, ketones, alcohols, nitriles, amides, acids, amines) substances with 5 C in the molecule are usually soluble in water those with branched carbon chains are more soluble. 

---