Aliphatic acids and related compounds

1 Straight Chain Aliphatic Acids and Related Esters, Alcohols 

Saturated n-alkanoic acids isolated recently from various lichen species include palmitic acid, stearic acid, nonadecanoic acid, eicosanoic acid (33) and the C26 — C34 acids (305). The unsaturated acids oleic acid (33), linoleic (304), linolenic and arachidonic acids (333) have also been identified in lichen extracts. Free n-alkanols (C15 — 23) have been isolated from 

Cetraria cucullata (55) and triglycerides (55, 216, 305) and wax esters (55, 304) from several species. The available evidence indicated that while C40 —C50 wax esters derived from n-alkanols n-alkanoic 

Further mixtures of tetrahydroxyalkanoic acids (36) have been isolated from several species 303, 304) and Alectoria fremontii 303) appears to produce n-alkyl (C6-C12) esters of such acids. 

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Iwasaki, I., Cooke, S.R.B. and Choi, H.S., Flotation, characteristics of hematite, goethite, and activated quartz with 18-carbon aliphatic acids and related compounds, Trans. AIME, 217, 237, 1960. 

Activated Quartz with C-18 Aliphatic Acids and Related Compounds, Trans. AIME, 220, 394... 

The acylation of enamines has been applied to the use of long-chain acid chlorides (388) and particularly to the elongation of fatty acids (389-391) and substituted aliphatic acids (392). The method has been used in the synthesis of the antineoplastic cycloheximide and related compounds (393-395) and in the acylation of steroids (396). Using an optically active chlorocarbonate, an asymmetric synthesis of lupinine could be achieved (397). 

Resonance Energies of Aliphatic Acids, Esters, Amides, and Related Compounds... 

Almost accidentally, Bienayme and Bouzid discovered that heterocyclic amidines 9-76 as 2-amino-pyridines and 2-amino-pyrimidines can participate in an acid-catalyzed three-component reachon with aldehydes and isocyanides, providing 3-amino-imidazo[l,2-a]pyridines as well as the corresponding pyrimidines and related compounds 9-78 (Scheme 9.15) [55]. In this reachon, electron-rich or -poor (hetero)aromatic and even sterically hindered aliphatic aldehydes can be used with good results. A reasonable rahonale for the formation of 9-78 involves a non-con-certed [4+1] cycloaddition between the isocyanide and the intermediate iminium ion 9-77, followed by a [1,3] hydride shift. 

Acyloxy- and acylthiopyrazines are convenient acylation reagents for benzylamine, aniline, pyrrolidine, and related compounds (see Section 6.03.8.3). The acylthio compounds are also useful for acylation of alcohols and phenols. Pyrazinyl alkyl sulfoxides (see Section 6.03.8.4) give aldehydes and ketones by treatment with TFAA <91H(32)937>. The pyrazinium chlorochromate salt (181) is formed by addition of chromium(VI) oxide to a solution of pyrazine in hydrochloric acid, and it has proved to be more effective for the oxidation of aliphatic and allyl alcohols to the aldehydes than pcc <83H(20)2029>. 

The iodine-catalyzed addition of carboxylic acids to styrene derivatives generated high yields of esters and related compounds (Scheme 2.17) [24], This transition metal-free reaction used TBHP as the oxidant and was carried out under very mild conditions using an assortment of alkenes and carboxylic acids as substrates. The chemistry was quite tolerant of preexisting functional groups, and even aryl bromides were retained through the oxidation process. In addition to the styrene derivatives, aliphatic alkenes such as 1-octene were also successfully converted into esters using this approach. 

The herbicide 2,4-D is itself a potent phytotoxin. However, a number of structurally related but inactive compounds may be converted by plants to 2,4-D following the activation process and thus act as herbicides. These phenoxyalkanoic acids are co-(2,4-dichlorophenoxy) alkanoic acids. The transformation may be viewed as shown in Fig. 12 as 6-(2,4-dichlorophenoxy)hexanoic acid as the parent compound. The sequence is called /1-oxidation because the steps in which two carbons are removed initially involve the oxidation of the /1-carbon to the aliphatic acid moiety. 

Compound 211 and several related compounds are readily accessible by stereospecific deprotonation of the appropriate optically active carbamic esters with 5-BuLi/TMEDA ° . Much of the knowledge about the stereochemical course of substitution in benzyUithium derivatives was obtained from experiments with these compounds. Only the reaction with proton acids, aliphatic aldehydes, ketones or esters as electrophiles proceed with retention for alkyl, silyl and stannyl halides, acid chlorides. 

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