Nitrogen and Oxygen Heterocycles

8-Dimethoxy-2(lH)-quinolines (235), which are key intermediates for the synthesis of antimalarial drugs, have been prepared in poor to moderate yields by intramolecular Wittig reaction of the salts (234). A combination of Wittig olefination and Claisen rearrangement of (2-hydroxy-4-prenyloxy)phenyl carbonyl compounds (236) has been used in a one-pot synthesis of 2, 3, 3 -trimethyl-2, 3 -dihydroangelicins (237).  

Both Wittig and Wadsworth-Emmons reactions have been used to synthesise functionalised oligo(vinylthiophenes) (245) for use as potential liquid crystal and non-linear optical materials.  

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Diverse Nitrogen and Oxygen Heterocycles via On-Resin Cyclization... 

Chiral 10 to 12-membered nitrogen and oxygen heterocycles, fused to isoxazo-line rings have been prepared with high regio- and stereoselectivity by INOCs of tethered N- and O-allyl carbohydrate derivatives. The use of a -Y-Ar-CH2 tether, containing a 1,2-disubstituted aromatic ring between the heteroatom attached to... 

Table 2. 13C-H coupling constant of chloroform in nitrogen and oxygen heterocyclic solvents...

The palladium catalyzed iminoannulation and carboxyannulation of alkynes and an appropriate aryl/vinyl halide is an efficient tool to construct six membered nitrogen and oxygen heterocycles. The process encompasses the concomitant formation of a carbon-carbon and a carbon-heteroatom bond. 

The increasing amounts of data available for simple fluoroheterocycles allow one to understand how the position of the fluorine substituent on a heterocycle can significantly affect its chemical shift. For all nitrogen and oxygen heterocycles, a fluorine substituent on a carbon bound to the nitrogen or oxygen will be deshielded compared to a fluorine at any other position. The situation is reversed for sulfur heterocycles, although the observed differences are small. 

During these five decades, the rearrangement has also evoked much interest in its extensions into the nitrogen and oxygen heterocyclic systems. The present review is an attempt to present some of the chemistry relating to nitrogen heterocyclic compounds wherein the... 

BEA zeolite can be also applied in the acylation of different heteroaromatic compounds. Thus, a series of sulfur, nitrogen, and oxygen heterocycles can be acylated with AAN. Some synthetic results are reported in Table 4.10. The best conversion and selectivity are achieved with BEA zeolite showing a surface area of 350-620 m x g-p... 

Cyclohydrocarbonylation (CHC) is defined as process of hydroformylation of functionalized olefins followed by concomitant intramolecular nucleopbillic addition to tbe newly formed aldehyde moiety leading to a cyclized product (7). CHC reactions have been developed into sophisticated cascade reactions allowing for the formation of both bicyclic and polycyclic nitrogen and oxygen heterocycles (136). 

Poly(styrene-co-allyl alcohol) can be esterified under microwave solventless conditions to give the polymers that are effective precursors for the preparation of various nitrogen and oxygen heterocycles. The reaction were carried out in an open vessels that were placed in a domestic microwave oven and irradiated for 10-20 min. In some cases, it was possible to scale-up the microwave procedure from 1 to 10 g scale. Under conventional thermal conditions, most of these experiments were run for 4 h in refluxing toluene solutions (Fig. 43) [138]. 

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