Mesoionic systems isomiinchnone

Although the mesoionic l,3-oxazolium-4-olates, isomiinchnones , occupied only a few pages in the reviews by Potts (1) and Gingrich and Baum (10), in the intervening years this ring system has exploded in popularity, largely due to the efforts of Padwa and co-workers. Padwa has summarized his isomtinchnone work in several reviews (22-27). While isomiinchnones are rarely isolable, these carbonyl... 

Prompted by our earlier work dealing with the internal dipolar cycloaddition reaction of mesoionic oxazolium ylides of type 74, we subsequently studied the rhodium(II) catalyzed reactions of the related a-diazo ketoamide system 154 <97JOC2001 04OL3241 05JOC2206>. Attack of the amido oxygen at the rhodium carbenoid produces a push-pull carbonyl ylide dipole (i.e., 155) that is isomeric with the isomiinchnone class of mesoionic betaines. 

Oxazoles 1, benzoxazoles 2, oxazolium salts 3, and oxazole A -oxides 4 are fully conjugated compounds (Figure 1). In addition, the two mesoionic structures l,3-oxazolium-5-olates 5 and (l,3-oxazolium-4-olates) 6, commonly known as miinchnones and isomiinchnones, respectively, are also considered to be conjugated rings. There are five systems of hydroxyl-substituted oxazoles and they exist in their oxo forms the 2(3H)-, 2(5H)-, 4(5//)-, 5(2//)-, 5(4//)-oxazolones 7-11. Three forms of dihydrooxazoles are known 2,3-, 2,5-, and 4,5-dihydrooxazoles respectively 12-14. The fully saturated ring is called oxazoline 15. The monooxo derivatives are 2-oxazolidinone 16,4-oxazolidinone 17, and 5-oxazolidinone 18. The three variants of oxazolidinediones are 19-21 and the fully oxidized oxazolidi-netrione is 22. 

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