Scope of Ru(II)-Catalyzed Synthesis of Pyridines from Alkynes and Nitriles

Journal of Organic Chemistry

Volumn 68, Issue 22, 2003, Pages 8595-8598

  Varela, Jesús A ^a   Castedo, Luis ^a   Saá, Carlos ^a  

^a UNIVERSITY OF SANTIAGO DE COMPOSTELA   (Spain)

Author keywords

[No Author keywords available]

Indexed keywords

CYCLOADDITION REACTIONS;

CATALYSIS; ELECTRONS; RUTHENIUM; SYNTHESIS (CHEMICAL);

ORGANIC COMPOUNDS;

ALKYNE; NITRILE; PYRIDINE; RUTHENIUM;

ARTICLE; CATALYSIS; CHEMICAL REACTION; CYCLIZATION; CYCLOADDITION; ELECTRON; SYNTHESIS;

EID: 0142258960     PISSN: 00223263     EISSN: None     Source Type: Journal    
DOI: 10.1021/jo035050b     Document Type: Article

References (35)

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24. 3NI), the reaction was much slower reaction (Br) or failed to take place. In the absence of chloride, only the dimer of 2a was observed. Reaction of malononitrile (3r) with 1,6-heptadiyne (2b) afforded the corresponding pyridine derivative, but with 1,7-octadiyne (2c) neither pyridine derivatives nor dimers of 2c were obtained.
25. 4, and evaporated to dryness under vacuum. Column chromatography of the residue on silica gel using ethyl acetate/hexane as eluent afforded the corresponding pyridine 4.
26. Methylcyanoformate and trichloroacetonitrile are also able to participate in [2 + 2 + 2] cycloadditions to afford pyridines, see ref 10.
27. In this case the reaction conditions were not optimized.
28. α,ω-Dinitriles and 1,2-dicyanobenzene also give good-to-excellent yields of 2-(ω-cyano)alkyl- and 2-[(2-cyano)phenyl]pyridines using Cp*Ru(COD)Cl, see ref 12.
29. Koelle, U.; Kang, B.-S.; Englert, U. J. Organomet. Chem. 1991, 420, 227.
30. Dinuclear Ru(II) complexes with dicyanamides have in fact been observed, see: Valerga, P.; Puerta, M. C.; Pandey, D. S. J. Organomet. Chem. 2002, 648, 27.
31. 2X-type complexes; see ref 17.
32. Ru(II)-catalyzed trimerization of n-hexyne failed, whereas methyl propiolate gave an almost quantitative yield of a mixture of isomeric 1,2,4- and 1,3,5-benzene derivatives. Moreover, as described above, only electron-poor nitriles and dinitriles have been able to participate in Ru(II)-catalyzed [2 + 2 + 2] cycloadditions with 1,6-diynes.
33. Traces of the 2,3,5-substituted pyridines (less than 3%) were also dedtected. The two pyridines are easily separated by chromatography. See the Supporting Information.
34. Starting nitriles were quantitatively recovered.
35. Methyl cyanoformate (3x) also undergoes cocyclization with 1,6-diyne 2a (giving the corresponding pyridine in quite good yield, see ref 10) but not with 2,2-dibut-2-ynyl malonic acid dimethyl ester, failure in this case probably being due to the location of the methyl α to the ruthenium in the ruthenacyle intermediate corresponding to 10.