Acid-catalyzed decomposition, acyl

Wl. Sawaki, Y., and Y. Ogata Acyl Migration in the Acid-catalyzed Decomposition of a-Hydroperoxy Ketones. J. Amer. Chem. Soc. 100, 856 (1978). 

II. Unimolecular Acid-Catalyzed Reactions Involving Acyl-Oxygen Fission. At least one instance is known in which decomposition of the protonated complex does not seem to depend upon the attack of water or an alcohol molecule. It is the formation or hydrolysis of esters of 2,4,6-trimethylbenzoic acid in sulfuric acid solution. Since cryoscopic studies have shown that the acid gives a molar freezing point depression of four (p. 39), and the ester five (p. 225), we must conclude that decomposition of the protonated complex to the acyl carbonium ion 0... 

Minisci-type substitution is one of the most useful reactions for the synthesis of alkyl- and acyl-substituted heteroaromatics. The acyl radicals are formed by the redox decomposition from aldehyde and /-butyl hydroperoxide or by silver-catalyzed decarboxylation of a a-keto acid with persulfate. Synthesis of acylpyrazines 70 as ant pheromones are achieved by this methodology using trialkyl-substituted pyrazines 69 with the acyl radicals generated from aldehydes or a-keto acids (Equation 10) <1996J(P1)2345>. The latter radicals are highly effective for the acylation. Homolytic alkylation of 6-chloro-2-cyanopyrazine 71 is performed by silver-catalyzed decarboxylation of alkanoic acids to provide 5-alkyl-substituted pyrazines 72 (Scheme 18) <1996CCC1109>. 

Nearly all the water-soluble vitamins are heterocyclic compounds. Among the first to be isolated was thiamine (vitamin Bi) (62), deficiency of which causes degenerative changes in the nervous system, including the multiple peripheral neuritis characteristic of beriberi. Thiamine deficiency can arise from decomposition of the vitamin by bacteria in the gut. In mammalian metabolism the hydroxy group of thiamine is esterified to give cocarboxylase (thiamine pyrophosphate) which catalyzes the decarboxylation of a-keto acids to aldehydes, acyloins or acids, and their transformation into acyl phosphates. 

The nitrogen extrusion from 1-pyrazolines and 3H-pyrazoles giving cyclopropanes and cyclopropenes, respectively, has been extensively reviewed The cyclopropane synthesis from 1-pyrazolines can be executed thermally as well as photochemically, but the latter method generally gives substantially better results than the former. The major side reaction observed in the thermal process is the production of olefins, which arise in the migration of a substituent from the C(4) to C(3) position. A retro-1,3-dipolar addition producing a diazoalkane and an olefin has been observed in certain cases. The decomposition of 3-acyl- or 3-alkoxycarbonyl-1-pyrazolines is catalyzed by acids, such as perchloric acid and boron trifluoride and by Ce The stereochemical course... 

The mechanism proposed for the Curtius degradation starts with the activation of carboxylic acid 119 by the (Boc)20, catalyzed by Zn(OTf )2, to generate carbonic anhydride 120, which is attacked by the azide ion to provide the unstable acyl azide 121 and sodium t-butoxide as a byproduct (Scheme 26). Next, isocyanate 122 is obtained by the decomposition of intermediate 121 with extrusion of N2. Reaction with sodium t-butoxide provides the desired carbamate 112. 

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