Acyl , interconversion

A sequence of straightforward functional group interconversions leads from 17 back to compound 20 via 18 and 19. In the synthetic direction, a base-induced intramolecular Michael addition reaction could create a new six-membered ring and two stereogenic centers. The transformation of intermediate 20 to 19 would likely be stereoselective substrate structural features inherent in 20 should control the stereochemical course of the intramolecular Michael addition reaction. Retrosynthetic disassembly of 20 by cleavage of the indicated bond provides precursors 21 and 22. In the forward sense, acylation of the nitrogen atom in 22 with the acid chloride 21 could afford amide 20. 

This chapter covers not only nuclear and extranuclear quinoxahnecarboxylic acids (and anhydrides) but also the carboxylic esters, acyl halides, carboxamides, carbohydrazides, carbonitriles, carbaldehydes, and (ketonic) acyl derivatives of quinoxaline a few related speceis are also included. To avoid repetition, the interconversions of these quinoxaline derivatives are discussed only at the first opportunity thus the esterification of quinoxalinecarboxylic acids in covered as a reaction of carboxylic acids rather than as a preparative route to carboxylic esters, simply because the section on carboxylic acids precedes that on carboxylic esters. To minimize any confusion, appropriate cross-references have been inserted. 

These are phosphoacylglycerols containing only one acyl radical, eg, lysophosphatidylcliolme (lysoleci-thin), important in the metabohsm and interconversion of phosphohpids (Figure 14—9).lt is also found in oxidized hpoproteins and has been imphcated in some of their effects in promoting atherosclerosis. 

A. Phosphoenolpyruvate.—The mechanisms of hydrolysis of phosphate esters of phosphoenol pyruvic acid (33) have been described in detail, and 0 studies confirm an earlier postulate that attack by water on the cyclic acyl phosphate (34) occurs at phosphorus and not at carbon. In the enolase reaction, the reversible interconversion of 2-phosphoglyceric acid(35)... 

This enzyme [EC 5.1.3.9], also known as A -acetylglucos-amine-6-phosphate 2-epimerase, catalyzes the interconversion of A -acylglucosamine 6-phosphate to A -acyl-mannosamine 6-phosphate. 

Scheme 7 Interconversion of Cyclic Tripeptides into Cyclols and Piperazine-2,5-diones Dehydration to Acyl-imidamide is an Almost Irreversible Transformation1199-202-2031...

Instruments that can be employed to measure energy barriers in acyl heterocycles should thus be able to follow these interconversion processes that occur in the energy range between 4 and 80 kJ mol". Furthermore, detection of separate conformers in equilibrium is an important intrinsic feature of experimental methods for quantitative population analysis while its sensitivity limits accuracy in measuring biased equilibria. 

The effect of the size of the acyl group on the barrier for isomer interconversion was examined (82JOC3890) in oxazolidine derivatives 103. The energy barrier, which amounts to 72.8 kJ mor when R = Me, decreases to 53.2 kJ mol when R is an adamantyl group. 

The chroman ring system is stable to organometallic reagents, for example in the formation of the tertiary alcohol (690) in high yield (63HCA650), and to the usual interconversion of carboxylic acid, acyl chloride, carboxamide and nitrile. 

---