Nitrogen-containing heterocyclic systems

The 4-unsaturated-5-oxazolones provide convenient starting materials for the synthesis of other nitrogen-containing heterocyclic systems. The preparation of tetrazoles and isoquinolines is discussed in Sections II,B, 1 and II,B,2,b. 

The initial success of the reactive dyes based on the triazine ring system was immediately followed by intense research activity into the possibilities offered by other related nitrogen-containing heterocyclic systems. Numerous systems have been patented as fibre-reactive groups although only a few of these have enjoyed significant commercial success. Some examples are illustrated in Figure 8.2. They include the trichloro-pyrimidines 176, the dichloropyridazines 177, the dichloroquinoxalines 178 and the chlorobenzothiazolyl dyes 179. 

The synthesis of nitrogen containing heterocyclic systems by photocylo-addition processes is virtually limited to examples involving [ 2 + 2] cycloaddition of imines, nitriles, and azo compounds. Successful additions are few in number and the requirements for success uncertain. The reactions do not proceed with the facility with which carbonyl containing compounds undergo photocycloaddition to alkenes to give oxetans, and various explanations have been advanced to account for this observed lack of reactivity.226... 

A wide variety of photoadditions to unsaturated nitrogen containing heterocyclic systems has been reported. It has, however, proved difficult to classify these processes as the reaction mechanisms involved have not always... 

The present review contains data on the synthesis of various nitrogen-containing heterocyclic systems based on isatoic anhydrides that have appeared in the press since 1980. It covers both the direct transformations of these anhydrides into such systems and processes leading at the first stage to the formation of anthranilic acid derivatives that are then transformed into the heterocyclic compounds in one or several stages. It is important that such transformations result in the formation of new heterocyclic systems. 

If nitrogen-containing heterocyclic systems are used, the halogen atom becomes more reactive, and this is an elegant preparation method for azaphenothiazine derivatives. 

Abstract Carbon d ylide dipoles are important intermediates with great application in heterocyclic chemistry. Here, we show how the rhodium-catalyzed a-diazocarbonyl compounds are employed in the generation of carbonyl ylides and their effective use for the synthesis, as well as functionalization, of heterocycles. Herein we discuss recent advancements in this field mainly describing the synthesis and importance of various oxygen-and nitrogen-containing heterocyclic systems and natural products from a-diazocarbonyl compounds. 

Herein rhodium-catalyzed inter- and intramolecular cycloadditions of carbonyl ylides derived from a range of diazocarbonyl compounds leading to oxygen- and nitrogen-containing heterocyclic systems and natural products are discussed. We have focussed on the last five years for the most significant developments of the reactions of carbonyl ylides derived from diazocarbonyl compounds. 

Several nitrogen-containing heterocyclic systems have been identified in the order Astrophorida. Of these, three azetidine derivatives isolated from species of the genus Penares are inhibitors of protein kinase C (Kobayashi et al, 1991a, 1996b Alvi, Jaspars, and Crews, 1994). 

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