Synthesis of N-heterocycles

Free-radical cyclization in the synthesis of N-heterocycles 97T17543. 

Synthesis of N-heterocycles using ureas and related compounds 98UK333. 

Synthesis of N-heterocycles with C—N bond formation catalyzed by transition metal catalysts 97SL749. 

Unsaturated germanates and stannates in the synthesis of N-heterocycles by [2-1-3] cycloaddition 98KGS1155. 

In the synthesis of N heterocycles, this technique also overcomes competitive retro Michael addition that lowers the yield of 1,4-adduct in the Michael addition of amines to nitro olefins. Thus, a toluene solution of nitro olefin 159 was treated with allylamine 160, EtgN, and TMSCI under nitrogen at ambient tern-... 

The 5-dig-mode of cyclization has been applied in the synthesis of N-heterocycles. For example, treatment of the /i-allenyl dithiosemicarbazide 37 with Bu3SnH and AIBN in hot benzene furnishes the substituted 3H-pyrrole 38 in 41% yield and the isomeric heterocycle 39 in 30% yield (Scheme 11.13) [68], Iminyl radical 40 is formed via Bu3Sn addition to the thiocarbonyl group of the radical precursor 37 and fragmentation of the adduct (not shown). Nitrogen-centered radical 40 adds 5-dig-selectively to provide substituted allyl radical 41. The latter intermediate is trapped by Bu3SnH to furnish preferentially product 38 with an endocydic double bond. 

The iminium salt photoaddition reaction has been applied to the synthesis of N-heterocyclic systems (equation 70)126,127. 

The cyclizahon of amino alcohols should be an attractive method for the synthesis of N-heterocyclic compounds, mainly because they can be obtained in a single step and without the generation of wasteful byproducts. Carbon-nitrogen bond formation catalyzed by Cp lr complexes has been extended to the synthesis of N-hetero-cyclic compounds by the cyclization of amino alcohols. 

The direct electrochemical methoxylation of furan derivatives represents another technically relevant alkoxylation process. Anodic treatment of furan (14) in an undivided cell provides 2,5-dimethoxy-2,5-dihydrofuran (15). This particular product represents a twofold protected 1,4-dialdehyde and is commonly used as a C4 building block for the synthesis of N-heterocycles in life and material science. The industrial electroorganic processes employ graphite electrodes and sodium bromide which acts both as supporting electrolyte and mediator [60]. The same electrolysis of 14 can be carried out on BDD electrodes, but no mediator is required The conversion is performed with 8% furan in MeOH, 3% Bu4N+BF4, at 15 °C and 10 A/dm2. When 1.5 F/mol were applied, 15 is obtained in 75% yield with more or less quantitative current efficiency. Treatment with 2.3 F/mol is rendered by 84% chemical yield for 15 and a current efficiency of 84% [61, 62]. In contrast to the mediated process, furan is anodically oxidized in the initial step and subsequently methanol enters the scene (Scheme 7). 

Intramolecular Michael and anti-Michael addition at the triple carbon-carbon bond in the synthesis of N-heterocycles 93SL369. 

New synthesis of N-heterocycles on rearrangement of spiro-5-isoxazo-lines 93SL1. 

Synthesis of N-heterocycles from (vinylimino)phosphoranes and related compounds 93MI21. 

Synthesis of N-heterocycles by condensation with carbonyl compounds... 

The use of internal nucleophiles in the Beckmann reaction has be i demonstrated to be an effective method for the synthesis of N>heterocycles. Substituted pynolines are readily available via diis qiproach, as exemplifled in equation (28). ... 

Beckmann reactions (rearrangement and rearrangement-cyclization) in synthesis of N-heterocycles 880R(35)1. 

Chloro-2-aza-2-propeniminium units as building blocks in synthesis of N-heterocycles 88S655. 

Dipolar cycloaddition in synthesis of N-heterocycles 85MI5 87YGK269 88H(27)981. 

N-Vinyliminophosphoranes in synthesis of N-heterocycles 90YGK681. 2. Oxygen Heterocycles... 

Rhee, J. U., Bliss, B. I., RajanBabu, T. V. A New Reaction Manifold forthe Barton Radical Intermediates Synthesis of N-Heterocyclic Furanosides and Pyranosides via the Formation of the C1-C2 Bond. J. Am. Chem. Soc. 2003,125,1492-1493. 

A general review on the use of electrochemical methods for the synthesis of N-heterocycles and natural products includes a section on imidazole derivatives. Thin-layer chromatographic methods for the separation of imidazole alkaloids have been briefly reviewed. Pharmacological effects of pilocarpine (15) have been summarized as part of an excellent review on convulsant alkaloids. ... 

Azoalkenes, transformation into N-heterocycles 86OPP301. Azomethineimines, synthesis of N-heterocycles from 78CLY921. 

N-N Bond scission and synthesis of N-heterocycles 86UK1785. Carbodiimides, formation of N-heterocycles from 82UK848 81AG855. Catalytic synthesis of N-heterocycles 83KGS1587, 83YGK604. Condensed N-heterocycles, syntheses using modified Japp-Klingemann... 

Double Michael reaction in synthesis of N-heterocycles 86YGK96. Electrophilic heterocyclization of unsaturated amino compounds into... 

Electroreduction in synthesis of N-heterocycles 85YGK496. Electrosyntheses of N-heterocycles 80H(14)l603. 

Geminal bifunctional compounds in synthesis of N-heterocycles 84YZ205. N-Heterocyclization with NHj elimination 78UK537. 

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