Oxazoline,Thiazolin und Pyrazolin als Heterodienophile in der [4+2]-Cycloaddition mit inversem Elektronenbedarf

Oxazolines, Thiazoline and Pyrazoline as Heterodienophiles in [4+2] Cycloadditions with Inverse Electron Demand The electron rich C=N bonds in the oxazolines 5a – b and 10 , in the thiazoline 7 and in the pyrazoline 13 are effective dienophiles towards the s-cis-azine system in the tetrazines 1a – b . Through [4+2] cycloaddition and elimination of nitrogen novel fused derivatives of triazine, such as 6, 8 and 15 , are formed.     

Imidazole,Oxazol und N-Methylpyrazol als Dienophile in der Diels-Alder-Cycloaddition mit inversem Elektronenbedarf

Imidazoles, Oxazole and N-Methylpyrazole as Dienophiles in the Diels-Alder-Cycloaddition with Inverse Electron Demand. We describe [4+2]-cycloadditions of various electron rich heteroaromatic compounds e.g. imidazole, substituted imidazoles, oxazole and N-methylpyrazole with the s-cis-fixed diazadien system of 3,6-bis(trifluoromethyl)-1,2,4,5-tetrazine and subsequent reactions. The reaction products are novel annulated and/or substituted pyridazines, respectively.     

4-(β-D-Ribofuranosyl)pyridazine: Neue C-Nukleoside durch [4+2]-Cycloaddition mit inversem Elektronenbedarf

4-(β-D-Ribofuranosyl)pyridazines: Novel C-Nucleosides by [4+2]-Cycloadditions with Inverse Electron Demand. A route for synthesizing novel C-nucleosides with 3,6- and 3,5,6-substituted pyridazines as heterocyclic aglycones is described. [4+2]-Cycloadditions of the alkyne substituted precursors 1 and 10a-d with the 1,2,4,5-tetrazines 2a,b , containing a highly reactive diazadiene system, lead to the O-protected 4-(β-D-Ribofuranosyl)pyridazines 4a,b and 12a-d , respectively. Subsequent deprotection yields the novel C-nucleosides 5a and 13a-d , respectively, in medium to good yields.     

Cyanamid als Seitenkettendienophil in der intramolekularen [4+2]-Cycloaddition Mit 1,2,4,5-Tetrazinen

Cyanamide as Side-chain Dienophlle In the Intramolecular [4+2]-Cycloaddition with 1,2,4,5-Tetrazines Including cyanamide as side-chain dienophile we expand the scope of the intramolecular Diels-Alder reaction of 1,2,4,5-tetrazines and describe synthetic routes to novel fused heterobicycles such as 1,4-oxazino-, 1,4-thiazinoand pyrazino[2,3-c]-1,2,4-triazines 12a-d, 17a,d, and 22c,d, respectively.     

Heterocyclisch anellierte Indolizine durch intramolekulare [3 + 2]-Cycloaddition mit Nicotinium-dicyanmethyliden

Heterocyclically Annulated Indolizines by Intramolecular [3 + 2]-Cycloaddition with Nicotinium-dicyanomethylides Thermally induced intramolecular [3 + 2] cycloaddition reactions of the nicotinium dicyanomethylides 4a - c , containing different ω-alkyne sidechains as substiuents at the pyrrolidine nitrogen, lead to the corresponding novel, heterocyclically annulated indolizines 6 - 8 in high yields. The dicyanmethylide 9 bearing an activated side chain dipolarophile yields the naph-thyridine 14 in small amounts besides the indolizine 11 .     

Synthese schwefelhaltiger,anellierter Indolizine durch intramolekulare [3+2]-Cycloaddition mit Pyridinium-methyliden

Synthesis of Sulfur Containing Annulated Indolizines by Intramolecular [3+2] Cycloaddition with Pyridinium Methylides Thermally induced intramolecular [3+2] cycloaddition reactions of the pyridinium methylides 3, 8a , and 8b , substituted with sulfur containing alkynyl side chains of different length lead to novel heterocyclically annulated indolizines 5 , 9 , and 11 in high yields.     

Über die [3+2]-Cycloaddition von Nitronen und Isothiocyanaten

[3+2]Cycloaddition Reactions of Nitrones with Isothiocyanates Cyclisation of nitrones 1 with isothiocyanates 2 commonly leads to 1,2,4-oxadiazolidine-5-thiones 3 , in some rare cases however to 1,2,4-oxadiazolidine-5-ones 4 . Glyoxal dinitrones 8 undergo reaction with isothiocyanates (isocyanates) to yield the products 9 and 10 , respectively.     

Zentralwirksame 4-Phenylpyrane: Hydrierte Phenylchromene,Phenylaza- und Phenyloxachromene sowie Phenyl-oxa- und Phenyldioxaxanthene durch [4+2]-Cycloaddition

Centrally Acting 4-Phenylpyrans: Hydrated Phenylchromenes, Phenylaza- and Phenyloxachromenes, Phenyloxa- and Phenyldioxa-xanthenes Obtained by (4+2-Cycloaddition [4+2]-Cycloadditions of the enamines la and lb , 7a - 7d , and 9a and 9b with the enones 2a and 2b and lla - llc yield the hydrated and amine-substituted, pyran-fused benzene, pyridine, pyran, benzopyran and pyranopyran derivatives 3a - 3c , 8a - 8d , 10 , 12 , 13a , 13b and 14a . By treatment with acids, these compounds can be converted to the corresponding phenylpyrans. Thus, 3a for example yields the tetrahydrobenzopyrancarboxylic acid 6 .     

Naphthalin und donorsubstituierte Naphthaline als Dienophile gegenüber 1, 2, 4, 5- Tetrazin-3,6-dicarbonsäure-dimethylester

Naphthalene and Donor substitutes Naphtalenes as Dienophiles towards Dimethyl 1,2,4,5-Tetrazin-3,6-dicarboxylate Inverse electron demand [4+2]cycloaddition reactions of dimethyl 1,2,4,5-tetrazin-3, 6-dicarboxylate (1) with naphthalene and various in lor 2-position donor substituted naphthalenes are described, which lead to novel benzo[f]phthalazine derivatives.     

Synthese des ersten 1,2,4-Triazin-C-Nukleosids und dessen Umwandlung in neue Pyridin-C-Nukleoside durch “inverse” [4 + 2]-Cycloaddition

Synthesis of the First 1,2,4-Triazine C-Nucleoside and its Transformation to Novel Pyridine C-Nucleosides by “Inverse” [4 + 2]-Cycloaddition Reactions The anomeric C-glycosyl precursors 6 und 7 , appropriate for C-nucleoside synthesis and functionalized by an imidate group, were prepared. They were utilized as heterodienophiles in a Diels-Alder reaction with inverse electron demand to yield the O-benzyl protected 5-(β- and 5-(α-D -ribofuranosyl)-1,2,4-triazines 9 and 10 , derivatives of a new class of C-nucleosides. 9 could be deprotected by hydrogenolysis with Pd/C as catalyst to furnish the hitherto unknown C-nucleoside 11 . The aglycon of 9 contains a diazadiene system, activated by electron withdrawing substituents, which reacts with various electron rich dienophiles like ketene acetals, enol ethers or enamines in an inverse [4 + 2]-cycloaddition reaction. After N₂-elimination the O-benzyl protected 2-(β-D -ribofuranosyl)-pyridines 13, 15, 17, 19 and 21 are formed. Removal of the protecting benzyl groups from the glycon moiety of 13, 15 und 17 leads to the novel 2-(β-D -ribofuranosyl)-pyridines 22 – 24 . Using the O-benzoyl protected thioimidate 25 as dienophile the reaction with the tetrazine 8 yields the 5-(furane-2-yl)-1,2,4-triazine 28 as sole product besides benzoic acid.     

[4+1]-Cycloaddition von Benzylisonitril an cyclische Azadiensysteme des 1,2,4,5-Tetrazins und 1,2,4-Triazins

[4+1]-Cycloaddition of Benzyl Isonitrile with Cyclic Azadiene Systems of 1,2,4,5-Tetrazines and 1,2,4-Triazines Various donor substituted 1,2,4,5-tetrazines 1a-e and 1,2,4-triazines 7a,b react with benzyl isocyanide in a sequence of [4+1]-cycloaddition and [4+2]-cycloreversion steps to yield the unstable antiaromatic intermediates 4 and 8 , respectively. Subsequent [1,5-H]-shift leads to the corresponding azomethines. The pyrazoles 5a-e are isolable in high yields as stable crystalline compounds, whereas the pyrroles 9a and b are hydrolyzed by SiO₂/H₂O to yield benzaldehyde and the aminopyrroles 10a and 10b .