728946-56-3Relevant academic research and scientific papers
Cobalt-templated radical processes: Inter- and intramolecular coupling of propargyl radicals
Melikyan, Gagik G.,Deravakian, Asatour,Myer, Steven,Yadegar, Sarkhadoun,Hardcastle, Kenneth I.,Ciurash, Joana,Toure, Pogban
, p. 68 - 75 (1999)
A novel method for radical C-C bond formation in the α-position to Co2(CO)6-clusters has been elaborated. The two-dimensional exploration of the process resulted in the discovery of structurally diverse O- and S-containing organic molecules capable of acting as efficient mediators in reductive coupling reactions, and in the elaboration of the preparative synthesis of 3,4-disubstituted 1,5-alkadiynes and carbocycles with eight- and nine-membered rings.
Cobaltocene-induced low-temperature radical coupling reactions in a cobalt-alkyne series
Melikyan, Gagik G.,Rivas, Bianca,Harutyunyan, Stepan,Carlson, Louis,Sepanian, Ruth
, p. 1653 - 1663 (2012/04/23)
A novel method for the low-temperature generation of Co2(CO) 6-complexed propargyl radicals is developed. It consists of an in situ preparation of the respective cationic species (-50 to -10 °C) and their rapid reduction with cobaltocene, Cp2Co, at -50 °C. The optimized experimental protocol is applied to both inter- and intramolecular reactions, affording topologically diverse α-aryl and α-napthyl, d,l- and meso-1,5-hexadiynes and 1,5-cyclodecadiynes. The d,l configuration is the most preferable steric arrangement in intermolecular radical C-C bond-forming reactions (d,l 69-92%), while a reversal of stereoselectivity is observed in intramolecular cyclizations (meso 79%). Under oxidizing conditions (Ce4+), decomplexation affords d,l-3,4-diaryl- and d,l-3,4-(1-/2-naphthyl)-1,5-hexadiynes in good to excellent yields (47-98%). An enhanced functional tolerance is showcased by introducing peripheral acid-sensitive functionalities, such as benzyloxy and methylenedioxy groups, and carrying out a five-step conversion scheme-from commercial aromatic aldehydes to radical dimers-under nonacidic conditions.
Cobalt-complexed propargyl cations: Generation under neutral conditions and spontaneous, high-temperature conversion to propargyl Radicals
Melikyan, Gagik G.,Sepanian, Ruth,Spencer, Ryan,Rowe, Aaron,Toure, Pogban
, p. 5541 - 5549 (2010/01/06)
A novel method for the generation of Co2(CO)6- complexed propargyl cations under neutral conditions is developed. The optimized experimental protocol involves treatment of the respective Co 2(CO)6-complexed prop
Tetrahydrofuran-mediated stereoselective radical C-C bond formation in dicobalthexacarbonyl-propargyl complexes
Melikyan, Gagik G.,Villena, Ferdinand,Florut, Arthur,Sepanian, Steve,Sarkissian, Hagop,Rowe, Aaron,Toure, Pogban,Mehta, Dutt,Christian, Nolan,Myer, Steven,Miller, David,Scanlon, Stephanie,Porazik, Maria,Gruselle, Michel
, p. 4680 - 4690 (2008/10/09)
An extensive study on the mechanism of novel tetrahydrofuran (THF)-mediated coupling of Co2- (CO)6-complexed propargyl alcohols and cations was carried out. On the basis of the stoichiometry of the process, the measurement of the kinetic isotope effect (KIE) in the competitive and noncompetitive settings (THF-d0 and THF-d8), ligand substitution experiments with 13CO, kinetic studies with model compounds-Co2(CO)6-complexed 1-phenyl-2-propyne (6), tetrahydrothiophene, cobalt-alkyne anchored tetrahydropyran (THP, 21)-and ab initio calculations, the mechanism of the reaction was proposed. It includes a reversible coordination of two THF molecules with an α-cationic center in a π-bonded propargyl moiety, followed by a single-electron transfer from the THF-sandwiched cobalt complex toward an electron-deficient propargyl cation. Although used in a 2-fold excess, THF acts as a catalyst, altering, both electronically and structurally, the requisite Co2(CO) 6-complexed cations and breaking away from the organometallic scaffold, upon radical generation, in a chemically unchanged form. By triggering disproportionation between cobalt-complexed propargyl cations, THF acts in an unusual capacity of a radical mediator, previously being known in organic chemistry as a Lewis donor and donor of H atoms and hydride ions. The novel process that provides a facile entry to d,l-3,4-diphenyl-1,5-hexadiyne can be expanded toward stereo-, chemo-, and regioselective synthesis of polysubstituted d,l-3,4-diaryl-1,5-alkadiynes otherwise hardly accessible.
