Other N-containing Heterocycles

This reaction was performed in a domestic MW oven for 9-15 min at a power level of 480 W. The yields were good (76-88%) and triazines 44 were obtained with high diastereoselectivity in favor of the cis isomers ( 96 4). This ratio is much higher than that from a comparable experiment in which the reaction was performed under traditional heating conditions. With the same reaction times and temperature (90 °C, measured directly after irradiation) product yields were significantly lower (19-31%) and diastereoselectivity ( 56 44) was much lower. 

The alkyl azide is generated in situ from the corresponding alkyl halides and sodium azide, whereupon it is captured by copper(I) acetylide forming the desired triazole 45. The reaction is performed under the action of MW irradiation for 10 min at 125 °C. Although most compounds readily tolerated this temperature, occasionally it resulted in reduced yields. To circumvent these problems these reaction mixtures were irradiated for 15 min at 75 °C. The reaction was performed in a 1 1 mixture of t-BuOH and water and the Cu(I) catalyst was prepared in situ by 

The final quinoxalinone product 48 was generated by de-Boc cyclization of 48 in TFA-THF (1 1) under the same MW conditions. The product 48 was easily separated from the reaction mixture by fluorous solid-phase extraction (F-SPE) in 51-95% yield. 

By use of sealed-vessel monomode MW technology full conversions were achieved within 10 min at temperatures of 100-140 °C. Solvent studies showed that the strongly MW-absorbing MeOH resulted in the best yields of the desired products. Initially the reaction was performed without the presence of a base. Although the amidine building block itself is a base, a catalytic amount of a stronger base (5% NaOMe) was necessary to obtain the desired product in high yield. 

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The scope of the Pd(II)-catalyzed enantioselective oxidation system has been the most extensively explored. The conditions are able to selectively oxidize a wide variety of benzylic alcohols with high selectivity (Table 1, entries 1-3,7) [4, 6-8]. Electron-withdrawing groups on the aromatic ring lead to lower oxidation rates and selectivity. Other types of aromatics can also be resolved successfully (entry 9), although N-containing heterocycles have little reactivity. Allylic and cyclopropyl alcohols are also well tolerated in the resolution (entries 5, 6), occasionally with extraordinary levels of selectivity (entry 4) [19]. As already mentioned, Sigman has shown that use of t-BuOH as solvent can also lead to useful enantioselective oxidation for some saturated alkyl alcohols (entries 10-12). 

Examination of the properties of N-borane adducts, e.g., 90, of piperidine, substituted piperidines and various other N-containing six-membered ring heterocycles constitutes an alternative approach to variable temperature NMR spectroscopy in that borane can be used as a locking agent for the observation of preferred conformers (cf. Scheme 35). In addition, the adducts can be very helpful for the assignment of the chemical shifts of the other substituents in the molecule as well as to acertain the configuration at the substituted positions (91T6903). 

As with other nitrogen-containing heterocycles, TV-alkylation is a reaction of some interest. This is particularly true when the products are nucleosides. One interesting example of nucleoside formation arises from reaction of a suitable furo[3,4-J]pyrimidine (41) and l-O-acetyl-2,3,5-tribe nzoyl-/ -D-ribose the product formed seems to be solvent dependent. The N-l substituted nucleoside (42 R = tribenzoylribose) is formed in 81 % yield when the heterocycle and the protected sugar are treated with tin(IV) chloride in acetonitrile. However, use of 1,2-dichloroethane as solvent affords only 17% of this product together with 81% of the N-l,N-3 disubstituted product (Equation (10)) <83CPB3074>. 

Two problems may be encountered here depending upon whether N-containing heterocycles (which may react as protonated and hydrogen-bonded species) or other heterocycles (hydrogen-bonding only) are considered. 

This article is a summary of our recent extensive study of tumor specificity (TS) and the type of cell death induced by N-containing heterocycles such as 4-trifluoromethylimidazole [22] and phenoxazine derivatives [23], by O-containing heterocycles such as 3-formylchromone [24] and coumarin derivatives [25,26], and by other compounds such as vitamin K2 and prenyl-alcohols [27]. 

The S,N-containing heterocyclic molecule l,3-dihydro-l-methyl-2tf-imidazole-2-thione (mimt), together with its thiol tautomer, have significant coordination potential which is likely to be susceptible to variations in pH and other reaction conditions. 

Heterocyclic compounds play a vital role in biological systems and are of immense importance in the fields of pharmaceuticals, agrochemicals, and also in other industrial points of view. Among N-containing heterocycles, 2-N-atoms containing 5-membered aromatic heterocycles are called pyrazole and imidazole, while 6-membered... 

Other compounds containing Al-N or Ga-N bonds, including heterocyclic compounds and cluster organometallic compounds, are considered in section 7.3.6. 

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