1.5- Dioxo - special

A special case of these ring transformation reactions is the 5-insertion reaction of 4-phenyl-1,2,4-triazolin-3,5-diones (4 Ph-TAD) [750PP251 81AG832, 81AG(E)797] into uracils, for example, the reaction of 5-(3,5-dioxo-4-phenyl-l,2,4-triazolidin-l-yl)-l,3-dimethyluracils with hydrazine... 

The H-NMR spectra of other closely related 2-mono- and 2,5-disubsti-tuted thiadiazolidines (78CB1915), and those of some 2-acetyl-3, 3-dimethyl-(80JOC482) and 3,4-dioxo-l,2,6-thiadiazolidines (75JOC2743 83IC2095), have also been published. No special features have been noticed in the spectra of 2,1,3-benzothiadiazoline 2,2-dioxides (71JCS(C)993 8OJHC383 81JMC13OO). 

It is important to note that a— BigCMoOJs has this active site with adjacent Mo dioxo groups. Such sites do not exist in the parent Scheelite structure ( ) (CaWOj, but with Bi, two adjacent Ca sites out of each six are vacant (indicated by dotted circles in Figure 5), leading to the special active site. 

Dioxo-l,3-oxazoUdines 1165, more commonly referred to as JV-carboxy-a-amino add anhydrides (NCAs) or Leudis anhydrides [816, 817], constitute a special dass of mixed anhydrides featuring simultaneous amino group protection and carboxy-late activation of a-amino acids. 

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