Syntheses by Transformation of Heterocycles

Syntheses (General Topics and Nonconventional Synthetic Methodologies, Synthetic Strategies and Individual Methods, Versatile Synthons and Specific Reagents, Ring Synthesis from Nonheterocyclic Compounds, Syntheses by Transformation of Heterocycles). 

Reagents, Ring Synthesis from Nonheterocyclic Compounds, Syntheses by Transformation of Heterocycles). 

Ring Syntheses by Transformation of Other Heterocyclic Systems... 

RING SYNTHESES BY TRANSFORMATION OF OTHER HETEROCYCLIC SYSTEMS 85... 

Carbon-carbon bond-forming reactions mediated by silicon Lewis acids in syntheses and transformations of heterocycles 03CRV733. 

Syntheses and transformations of heterocycles mediated by fluoride ion-activated organosilicon compounds 02H(57)361. 

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. 

The study on ring transformations of heterocycles is an attractive subject of research for many years. This great interest is due to the fact that these reactions are usually easily performed and that by these ring transformations heterocycles can be synthesized which are otherwise difficult to obtain. Moreover, unravelling the course of the ring transformation has always been a challenging problem and has attracted the interest of many chemists it requires studies on substituent and solvent effects, labeling and NMR studies, kinetic studies and quantum chemical calculations. In the course of... 

The syntheses of five-membered heterocycles containing three oxygen or sulfur atoms in the 1,2,3-positions can be classified into three groups (i) one-component syntheses, in which a suitable acyclic molecule is cyclized by linkage of two heteroatoms (ii) two-component syntheses, in which the ring is built up either by a [3 -f 2] process or a [4 -1-1] process and (iii) synthesis by transformation of another heterocyclic ring. 

Very many syntheses of isoxazoles from other heterocyclic compounds have been reported. The subject of ring transformations of heterocycles has been well reviewed35-37 and since many of the reactions are covered by the categories already discussed (the starting heterocycle serving merely as precursor of the appropriate intermediate), only a brief summary, with... 

Unless discussed below, there have been no new syntheses of these systems by transformation of other heterocycles. 

Formation and Ring Transformations of Heterocycles. 4-Methylthiazole, a fnngicide, can be synthesized by a vapor-phase reaction (116). Thus, Cs-loaded ZSM-5 zeolite gives excellent performance, for example, activity, selectivity, and life time. The reaction is run at 700 K in the presence of water vapor. 

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. 

Syntheses of heterocyclic compounds that are dealt with in this review are achieved either by cyclization of open-chain substrates under the action of organohypervalent iodine reagents or by carrying out several sequential transformations of substrate heterocyclic compounds using these reagents to obtain new heterocyclic derivatives. In this section, we cover the first strategy, leaving the second one for Section III. An area that is not covered... 

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