Imidazolone formation, amino

Knochel s method provided the pentameric peptide 224. Hydrogenation followed by treatment of the resulting amino acid with EDC and HOBt afforded macrocycle 225. Hydrolysis of methyl ester 225, and imidazolone formation via the acid chloride, followed by Boc deprotection provided kapakahine F (219) in significant quantity. Final coupling of 219 with Boc-Phe-OH followed by Boc removal afforded kapakahine B (218) (Scheme 40). 

Asaro, M. F. Nakayama, I. Wilson, R. B. Formation of sterically hindered primary vicinal diamines from vicinal and geminal dinitro compounds. /. Org. Chem. 1992, 57, 778-782. Rodriguez, H. Marquez, A. Chuaqui, C. A. Gomez, B. Oxidation of mesoionic oxazolones by oxygen. Tetrahedron 1991, 47, 5681-5688. Heras, M. Ventura, M. Linden, A. Villal-gordo, J. M. Reaction of a-iminomethylene amino esters with mono- and bidentate nucleophiles a straightforward route to 2-amino-lH-5-imidazolones. Tetrahedron 2001, 57, 4371—4388. 

Generally the yields of 2-aminooxazoles (37) are moderate to good with 2-amino-4,5-diphenyloxazole maximum yield of 91% has been obtained. Poor yields of the oxazoles are often accompanied by the formation of imidazoles and 2-imidazolones as by-products.104... 

Heating of 3-amino-2-picolinic acid azide in toluene for a short duration gave IP-2-one in 50% yield, whereas the thermolysis of 2-aminonicotinoyl azide in xylene led to the formation of the same imidazolone but in 90% yield. This imidazolone is also formed in a relatively poor yield ( 38%) on pyrolysis (210-220 °Q of both 3-aminopicolinoyl hydroxamic acid and its isomer, 2-aminonicotinoyl hydroxamic acid. In the latter case 2-aminonicotinic acid (59JCS3157) is formed as a by-product in 19% yield. 

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