Transformation of other heterocycles

A novel ring opening reaction of isoxazoles led to the formation of functionalized pyrroles 06S1021 . For example, treatment of isoxazole 52 with DBU led to the formation of pyrrole 53. A solid-phase synthesis of 3-amino-2,5-dicarboxylates was accomplished by transformation of pyrrol-3-one 54 06JCC177 . The reaction between 54 and secondary amines led to the corresponding resin-bound aminopyrroles after enamine formation and loss 

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These consider ring syntheses from non-heterocyclic compounds first, followed by transformation of other heterocyclics. Syntheses in which no new heterocyclic ring is formed are dealt with primarily in the appropriate reactivity section, but with cross-referencing when necessary. Ring syntheses from acyclic precursors are dealt with as logically as possible according to the number and nature of the new ring bonds formed in the process. 

In their review on the syntheses of aminofurazans, Andrianov and Eremeev (84CHE937, 84KGS1155) identified two major approaches to the preparation of these compounds (i) the preparation of aminoglyoximes, followed by dehydration, as a rule, with alkali, which is the more common methodology (Scheme 99) and (ii) transformations of other heterocycles. 

Ring Synthesis by Transformation of Other Heterocycles 5.08.10.1 Introduction... 

SYNTHESIS OF TRIAZOLES BY TRANSFORMATION OF OTHER HETEROCYCLIC SYSTEMS... 

A number of examples of the transformation of other heterocycles into 1,2,3-thiadiazoles were collected in the first edition <84CHEC-i(6)447>. Few other examples have since appeared one interesting case is the reaction of isothiazolone (41) with hydrazine to form a 1,2,3-thiadiazole (Equation (20)) <84JHC1679>. 

Ring Syntheses by Transformation of Other Heterocyclic Systems... 

This chapter discusses the transition metal catalyzed functionalization of such systems that fall outside the topic of Chapters 6 and 7, as well as certain other compound classes (e.g. purines, pyrones). In contrast to the abundant literature of the chemistry of five and six membered systems, the transition metal catalyzed transformations of other heterocycles have not been studied so far in the same depth, probably due to the limited availability of their halogen derivatives compared to haloazines and haloazoles. Purine compounds and their structural analogues constitute an exception, since their biological importance proved to be a strong drive for synthetic chemist worldwide.1... 

SYNTHESIS BY TRANSFORMATION OF OTHER HETEROCYCLES 3.12.4.1 Ring Contraction of Six-membered Heterocydes... 

Several reports concerning the synthesis of oxa/thia-2-azole rings by transformations of other heterocyclic rings appeared in CHEC-II(1996) <1996CHEC-II(4)535>. All new reports are classified in accordance with the size of the ring to be transformed. 

There are many ways to assemble the l,4-(oxa/thia)-2-azole ring system. Most of them are performed by inter- or intramolecular cyclizations of suitable acyclic precursors. In some instances, ring transformations of other heterocycles may be used, although the scope of these reactions has not been widely studied. The most important cyclizations are ... 

Tetrazoles from Transformations of Other Heterocyclic Rings 392... 

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