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Pyridine 1-imines*, cycloaddition

Cycloadditions where the 2ir component is an inline or iminium species have been much used for the synthesis of reduced pyridines and pyridones (B-87MI505-01), see also a general review of imine cycloadditions (87H(26)777). [Pg.526]

Alkenes, perfluoro-cycloadditions to benzyl azide, 60, 35 pyridine imines and ylids, 60, 36 Alkenes, perfluoro-, as heterocyclic precursors, 59, 10 Alkylation, free-radical, of 1,3-dimethyluracil, 55, 227 A-Alkylation, [ 1,2,4]triazolo[ 1,5-u)-pyrimidines, 57, 110 Alkynes, photocycloaddition to uracils, rearrangement with HCNO elimination, 55, 149 Alkynes, ethoxy-, cyclaoddition to hexafluoroacetone azine, 60, 32 Alkynes, perfluoro-, as heterocyclic precursors, 59, 10 Allenes... [Pg.355]

Reversible pyridine dissociation yields the non-Lewis base stabilized imido complex [Cp(NHAr) Ti=NAr] (54). This coordinatively unsaturated species undergoes a [2 + 2] cycloaddition reaction with allene to give an azatitanocyclobutane (55), which is then protonated to the /mamido complex. Elimination of enamine occurs followed by isomerization to the energetically more favorable imine. [Pg.290]

Closure of the oxadiazole ring is still achieved through cycloaddition between pyridine iV-oxides and isocyanates, affording adducts such as 142 (Scheme 38) <1995T6451>. Nonaromatic imine fV-oxides exhibited similar reactivities, since azasugar-derived fV-oxides as a mixture of 143 and 144 underwent cycloaddition reactions in the presence of phenyl isocyanate or trichloroacetonitrile. Compounds 145 and 146 (Scheme 39) were obtained from the aldoxime W-oxide 143 two other regioisomeric heterocycles arose from the ketoxime derivative 144 <1996T4467>. [Pg.607]

Extensive studies on diastereoselectivity in the reactions of 1,3-dipoles such as nitrile oxides and nitrones have been carried out over the last 10 years. In contrast, very little work was done on the reactions of nitrile imines with chiral alkenes until the end of the 1990s and very few enantiomerically pure nitrile imines were generated. The greatest degree of selectivity so far has been achieved in cycloadditions to the Fischer chromium carbene complexes (201) to give, initially, the pyrazohne complexes 202 and 203 (111,112). These products proved to be rather unstable and were oxidized in situ with pyridine N-oxide to give predominantly the (4R,5S) product 204 in moderate yield (35-73%). [Pg.505]

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). [Pg.550]

Hetero-Diels-Alder reactions provide an attractive means of rapidly constructing complex heterocyclic ring systems. Cycloaddition of pyrazolyl imines with a variety of electron-deficient dienophiles has been used to assemble pyrazolo[3,4,1 ]pyridines in a focused microwave reactor under solvent-free conditions53. The reactions proceeded in modest to excellent yield, depending upon the choice of diene and dienophile (Scheme 3.32). [Pg.59]

The formation and intramolecular dipolar cycloaddition of azomethine ylides formed by carbenoid reaction with C=N bonds has recently been studied by the authors group.84 Treatment of 2-(diazoace-tyl)benzaldehyde O-methyl oxime (176) with rhodium(II) octanoate in the presence of dimethyl acetylenedicarboxylate or N-phenylmaleimide produced cycloadducts 178 and 179, respectively. The cycloaddition was also carried out using p-quinone as the dipolarophile. The major product isolated corresponded to cycloadduct 180. The subsequent reaction of this material with excess acetic anhydride in pyridine afforded diacetate 181 in 67% overall yield from 176. The latter compound incorporates the basic dibenzofa, d -cyclohepten-5,10-imine skeleton found in MK-801,85 which is a selective ligand for brain cyclidine (PCP) receptors that has attracted considerable attention as a potent anticonvulsive and neuro-protective agent.86,87... [Pg.140]

Weinreb, S. M., Scola, P. M. N-acyl imines and related hetero dienes in [4+2]-cycloaddition reactions. Chem. Rev. 1989, 89,1525-1534. Marcelis, A. T. M., van der Plas, H. C. Diels-Alder reactions of diazines and pyridines. Trends Heterocycl. Chem. 1990, 1,111-123. [Pg.599]

Logothetis studied the thermal intramolecular azide-alkene cycloaddition (IAAC) of 5-azido-5-methyl-1-hexene and observed the formation of a mixture of imines and aziridines <65JA749>. The first case of utilization of silica gel in the selective decomposition of triazoline (35) to pyridines and aziridines (X = CH2—CH2, (CH2)3) was reported by Murthy and Hassner (Equation (17)) <87TL97>. The role of silica gel in the chemoselective reaction is still obscure, but it is likely that acidic surface... [Pg.75]

Taylor and Raw recently designed a tethered imine-enamine cascade sequence that converts 1,2,4-triazenes into substituted pyridines. In the presence of molecular sieves, A-methylethylenediamine (147) underwent condensation with excess cyclic ketone 148 (n — 1-4) to give imine-enamine 150 (04CC508). The enamine portion of the molecule then participated in an inverse-demand Diels-Alder cycloaddition reaction with 149 to provide intermediate 151. Cycloreversion of 151 with loss of N2 then gave 152 in which the tertiary amino group underwent addition to the adjacent imine functionality to afford zwiterionic 153. Finally, an intramolecular Cope elimination produced 154 in 74-100% yield. Several other triazines were also shown to participate in this novel cascade (Scheme 27). [Pg.20]

Arylideneanilines are converted into fused pyridines by heating with an alkyne and an oxidizing agent such as di-isopropyl peroxydicarbonate (DP) when the aniline is unsymmetrically substituted, a mixture of isomers may be formed [3173]. a-Halo ketones (and, less efficiently, simple aliphatic ketones [2639]) react with imines to give fused pyridines in variable yields [2715]. An imine formed by reaction of a 6-aminopyrimidinedione with DMFDMA undergoes cycloaddition with an electron-deficient alkene the first product is dehydrogenated in hot nitrobenzene [3620]. [Pg.650]

A three-component, one-pot process involving formation of a vinyl imine from a palladium(0)-catalysed coupling followed by the cycloaddition and then aromatisation via toluenesulflnate elimination gives bicy-clic 2-amino-pyridines. "... [Pg.163]


See other pages where Pyridine 1-imines*, cycloaddition is mentioned: [Pg.265]    [Pg.22]    [Pg.255]    [Pg.433]    [Pg.428]    [Pg.254]    [Pg.859]    [Pg.167]    [Pg.94]    [Pg.453]    [Pg.22]    [Pg.265]    [Pg.705]    [Pg.265]    [Pg.311]    [Pg.267]    [Pg.3]    [Pg.359]    [Pg.360]    [Pg.125]    [Pg.139]    [Pg.1419]    [Pg.94]    [Pg.453]    [Pg.719]    [Pg.327]    [Pg.1217]    [Pg.719]    [Pg.265]    [Pg.111]    [Pg.378]    [Pg.271]    [Pg.338]   


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