Unsaturated nitrogen heterocyclic

Among six-membered unsaturated nitrogen heterocycles, cycloaddition reactions of nitrile oxides at the C=N bond have been described for individual... 

Stanovnik and co-workers (100,101) systematically investigated the cycloaddition reactions of diazoalkanes with unsaturated nitrogen heterocycles, such as azolo-[l,5-fl]pyridines, pyridazin-3(2/7)-ones, and [fo]-fused azolo- and azinopyridazines. The Stanovnik group have studied the further transformations of the products and reviews of this chemistry are available. In a typical example, the reaction of 6-chlorotetrazolo[l,5-/7]pyridazine (37) with 2-diazopropane yields the NH,NH-dihy-dro-pyrazolo[4,3-(i]tetrazolo[l,5-/7]pyridazine 38 (102) (Scheme 8.11). The latter substrate reacts with acetone to produce an azomethine imine 39 that thermally rearranges to give the fused dihydro-1,2-diazepine 40. The azomethine imine obtained with glucose can be trapped with methyl acrylate to furnish the C-nucleoside 41 (103). 

The Chemistry of Unsaturated Nitrogen-Heterocyclic Compounds Containing Carbonyl Groups... 

A related intramolecular N-alkylation leading to saturated nitrogen heterocycles 99 can proceed via dehydration of intermediates 98 (Eq. 39) [96]. Unsaturated nitrogen heterocycles such as pyrroles [97], indoles [98], benzo-azoles [99], 2,3-dihydroimidazol-2-ones [100], and imidazo[l,2-a]pyridines [101] were obtained through similar cyclocondensation reactions. Interesting ruthenium-catalyzed syntheses of quinolines have been achieved by means of cyclocondensations of aniline derivatives with propanediols, aminoalcohols, or... 

As an extension of this chemistry, 7V-sulfinyl aziridine 188, prepared from (/ )-187, was utilized in the asymmetric synthesis of protein kinase C inhibitor D-e/yf/iro-sphingosine 189" and in the first enantioselective synthesis of the marine cytotoxic antibiotic (/ )-(-)-dysidazirine (190).100 This latter result constitutes the first general method for preparing nonracemic 2//-azirines, the smallest of the unsaturated nitrogen heterocycles.100,101... 

G. A. Lee, Simplified synthesis of unsaturated nitrogen-heterocycles using nitrile betaines, Synthesis (1982) 508-509. 

The generation of the carbcxi-carbon double bond of unsaturated nitrogen heterocycles by the rDA reaction of cycloadducts that act as protected ethylenes has been accomplished. Azetines have been prepared by this method. Another example is the synthesis of l-methyl-3-pyrroline (201). By protecting the ethylene of N-methylmaleimide (199) with furan and then reducing with lithium aluminum hydride, adduct (200) was obtained (equation 86). Pyrolysis of adduct (200) at 250-300 C gave l-methyl-3-pyrroline (201) in 60% isolated yield. The ethylene moiety of N-substituted maleimides can also be generated via rDA reactions. Examples include the generation of N-phenylmaleimide (equation 87) and of N-acetoxymaleimide (equation 88). ... 

Catalytic hydrogenation of unsaturated nitrogen heterocycles plays an important role in the synthesis of nitrogen-containing natural products such as alkaloids and amino acids. 

Pyridine C5H5N, an azabcnzeiie, or unsaturated nitrogen heterocycle with a six-meinbcrcd ring. 

Six-membered heterocycles Saturated as well as unsaturated nitrogen heterocycles have been prepared. The malononitrile derivative 139 underwent a ring-closure reaction with... 

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