- 1,3-Dipolar cycloaddition of azomethine imines to ethynyl hetarenes: A synthetic route to 2,3-dihydropyrazolo[1,2-a]pyrazol-1(5H)-one based heterobiaryls
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π-Deficient ethynyl hetarenes were used as dipolarophiles in a 1,3-dipolar cycloaddition reaction with azomethine imines (2-arylidene-5-oxopyrazolidin-2-ium-1-ides). Both CuI-catalyzed and catalyst-free thermally induced reactions proceeded with high regioselectivity providing 6-hetaryl-5-aryl-2,3-dihydropyrazolo[1,2-a]pyrazol-1(5H)-ones in moderate to excellent yields. The ethynyl hetarenes (pyridines, pyrazines, quinoxalines, pteridines and pyrimido[4,5-c]pyridazines) with ortho-methyl, ortho-cyano and ortho-alkynyl substituents were applicable to this reaction. 1,3-Dipolar cycloaddition reactions of alkynyl hetarenes with azomethine imines or other 1,3-dipole reagents can be considered as an alternative synthetic approach to heterobiaryls.
- Nelina-Nemtseva, Julia I.,Gulevskaya, Anna V.,Suslonov, Vitaliy V.,Misharev, Alexander D.
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p. 1101 - 1109
(2018/02/06)
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- Rapid Bergman cyclization of 1,2-diethynylheteroarenes
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The synthesis and cyclization of acyclic quinoxaline, pyridine, and pyrimidine enediynes (1-3) are described. These compounds were prepared using palladium(0) coupling of trimethylsilyl acetylene to o-dihalo- or o- halotriflic heteroarenes. All compounds were prepared in modest to good yields. The enediynes prepared were shown to undergo Bergman cyclization. Kinetics over a minimum of 3 half-lives were used to construct ]Arrhenius plots. Pyrimidine 3 was found to have an activation energy of 16.1 kcal/mol. Cyclization of the closest known aromatic analogue, o-diethynylbenzene (15), has E(a) = 25.1 kcal/mol (Grissom, J. W.; Calkins, T. L.; McMillen, H. A.; Jiang, Y. J. Org. Chem. 1994, 59, 5833-5835). Pyridine 2 and quinoxaline 1 gave activation energies of 21.5 and 33.6 kcal/mol, respectively. The results illustrate that heteroarenes can be used to activate Bergman cyclization. We expect these compounds to play an important role in furthering the understanding of Bergman cyclization and in aiding the development of new biologically significant enediynes.
- Kim, Chang-Sik,Russell
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p. 8229 - 8234
(2007/10/03)
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- One-step synthesis of dialkynyl-1,2-diones and their conversion to fused pyrazines bearing enediyne units
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A convenient procedure for the preparation of symmetrically end-protected dialkynyl-1,2-diones 3 from lithium acetylides and oxalyl chloride in the presence of CuBr and LiBr is described. The condensation of 3 with various aromatic and heteroaromatic 1,2-diamines leads to pyrazine-based α-dialkynylated heterocycles. The enediyne substructure of diethynylquinoxaline can be thermally rearranged in a Bergman cyclization reaction.
- Faust, Ruediger,Weber, Christian,Fiandanese, Vito,Marchese, Giuseppe,Punzi, Angela
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p. 14655 - 14670
(2007/10/03)
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- Preparation and Reactions of 2-Alkynyl-3-chloroquinoxalines.
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2-Alkynyl-3-chloroquinoxalines are prepared from 2,3-dichloroqionoxaline and alk-1-ynes: use of 2-methylbut-3-yn-2-ol, and the removal of acetone with base, yields 2-chloro-3-ethynylqionoxaline.The chloroalkynes are readily converted into pyrrolo- and thi
- Ames, Donald E.,Mitchell, John C.,Takundwa, Chisango C.
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p. 1683 - 1696
(2007/10/02)
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