Bicyclic Nitrogen Heterocycles Research Articles

Reaction of N-Vinylic Phosphazenes Derived from β-Amino Acids with Aldehydes. Azadiene-Mediated Synthesis of Dihydropyridines, Pyridines, and Polycyclic Nitrogen Derivatives

Enamino phosphonium salts 2 are obtained by 1,2-addition of hydrogen chloride to N-vinylic phosphazenes 1 derived from triphenylphosphine. Aza-Wittig reaction of phosphazenes 1 derived from triphenylphosphine and 6 derived from diphenylmethylphosphine with aldehydes 3 leads to the formation of 2-azadienes 7. Reaction of azadienes 7 with enamines affords dihydropyridines 9 and 11, pyridines 12, and bicyclic nitrogen heterocycles 15−18 in a regioselective fashion, while heterodiene 20 reacts in the same way with pyrrolidinocyclohexanone giving 1-azaphenanthrene compound 21. Reaction of enamino phosphonium salts 2 with aldehydes 3 gives symmetrical dihydropyridines 5.

Diastereoselective Cycloadditions of Nitroalkenes as an Approach to the Assembly of Bicyclic Nitrogen Heterocycles.

A three-component coupling for the rapid assembly of nitrogenated bicycles has been developed that employs the sequential cycloaddition of nitroalkenes as 4pi components and both an electron-rich vinyl ether and electron-withdrawing alkenes. Given the distinct electronic character of nitroalkenes and the intermediate nitronates, the coupling represents an atom-economy strategy without side products resulting from competitive reactions. Either with a racemic nitroalkene or an enantiopure nitroalkenyl sugar, these processes were regiospecific leading to the formation of bicyclic nitrosoacetals with high facial diastereoselectivity. The stereochemistry of the cycloadducts was assigned by NMR spectroscopic techniques, and those of 2 and 15 were corroborated by X-ray crystallographic analysis. The unmasking of the nitrosoacetal moiety under mild conditions represents a homologation route for higher aldehydo sugars.

Synthesis of Nitrogen Heterocycles using Tandem Radical Cyclisation of Imines

Bicyclic nitrogen heterocycles have been synthesized by tandem cyclisation of sp3 carbon-centred radicals onto the CN double bonds of imines to generate intermediate aminyl radicals, which undergo further cyclisation onto suitably positioned alkenes.

ChemInform Abstract: Synthesis of Novel Bicyclic Nitrogen Heterocycles by the Intramolecular Dipolar Cycloaddition Reaction of Nitrones with Allenes and Alkynes.

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Synthesis of nitrogen heterocycles using tandem radical cyclisation of imines

Bicyclic nitrogen heterocycles have been synthesized by tandem cyclisation of sp 3 carbon-centred radicals onto the CN double bonds of imines to generate intermediate aminyl radicals, which undergo further cyclisation onto suitably positioned alkenes. Bicyclic nitrogen heterocycles have been synthesised by tandem cyclisation of sp 3 carbon-centred radicals onto the CN double bonds of imines to generate intermediate aminyl radicals, which undergo cyclisation onto alkenes, e.g. the synthesis of spiroamines.

Synthesis of novel bicyclic nitrogen heterocycles by the intramolecular dipolar cycloaddition reaction of nitrones with allenes and alkynes

A study of the intramolecular dipolar cycloaddition reactions of a series of allenyl and alkynyl nitrones has been carried out. Phenylhydroxylamine readily reacts with o-(1,2-propadienyloxy)benzaldehyde to give a dioxaazabicyclo[3.2.1]octene. The intramolecular 3+2-cycloaddition of 2-(1,2-propynyloxy)benzaldehyde and N-methylhydroxylamine was also studied. In this case, the major cycloadduct formed was identified as 4-methyl-2,5- endo-oxo-2,3,4,5-tetrahydro[1,4]benzoxazepin. The formation of this novel rearranged product involves an initial dipolar cycloaddition across the acetylenic π-bond to give the expected 4-isoxazoline as a transient intermediate. The next step proceeds by homolysis of the O-N linkage and this is followed by ring closure to produce an aziridine which undergoes further C-C bond cleavage. The resulting azomethine ylide is converted to the final rearranged product by means of an ortho-quinone methide intermediate. Phenylsulfonyl activated allenes were also found to react with alkylhydroxylamines to give nitrones which undergo cycloaddition with the neighboring π-bond to afford the resulting bicyclic nitrogen heterocycles.

ChemInform Abstract: ENAMINES AND IMINIUM SALTS FROM AMIDO ACIDS

AbstractBei der Destillation der Carbonsäuren (I), (III), (VI) und (IX) (Synthesen im experimentellen Teil beschrieben) unter der gegebenen Reaktionsbedingung bilden sich bicyclische Enamine, die in Form der Salze (II), (IV), (VII) und (X) isoliert werden.

Enamines and iminium salts from amido-acids

Distillation of ω-carboxyalkyl lactams from soda-lime leads to the formation of bicyclic enamines or imines with concomitant loss of carbon dioxide and water. Monoamides of dicarboxylic acids afford cyclic ketones. A mechanistic rationale is presented and it is concluded that the reaction is a variant of the classical Ruzicka cyclization of dicarboxylic acids. The method allows the regiospecific formation of iminium salts of bicyclic nitrogen heterocycles.

Synthese und Additionsreaktionen von 1.3.2λ2.4-Diazaphosphoniaahiminatacyclobutanen [1] / Synthesis and Addition Reactions of 1,3,2λ2,4-Diazaphosphoniaaluminatacyclobutanes [1

Abstract N-silylated aminoiminophosphines react with aluminium trihalides to give acyclic zwitterions having two-coordinated phosphorus. At about room temperature these adducts decompose by elimination of silylhalide and formation of 1,3,2λ2,4-diazaphosphonia-aluminatacyclobutanes. Reaction of halogens and alkyl halides with the cyclic zwitterions results in formation of the corresponding 1,1-addition products. With alkyl-azides one obtains bicyclic phosphorus nitrogen heterocycles whilst in the reaction with trimethyl-silylazide the isomeric monocyclic azide derivative is formed. The IR and NMR spectra of the cyclic zwitterions are briefly discussed.