Gagik Melikyan - Academia.edu (original) (raw)
Papers by Gagik Melikyan
Organic Letters, 2002
The relative stabilities of thymidine-3',5'-dipho... more The relative stabilities of thymidine-3',5'-diphosphoric acid (1) derived isomeric cations and radicals were calculated and key geometric parameters were thoroughly analyzed. The most probable sites of a hydride-ion (1', 2', 5-Me) and H-atom (4', 5', 5-Me) abstraction were identified, thus allowing prediction of the regioselectivity of potential damage to the deoxyribose ring and thymine moiety caused by carcinogenic agents of electrophilic and radical nature. [structure: see text]
ChemInform, 1998
Reaction of Heterocyclic Aldehydes with Methyl Derivatives of Unsaturated γ-and δ-Lactones.
Organometallics, 2009
Under neutral conditions, Co2 (CO) 6-complexed propargyl methyl ethers, upon treatment with trifl... more Under neutral conditions, Co2 (CO) 6-complexed propargyl methyl ethers, upon treatment with triflic anhydride, can be converted to the respective propargyl cations, which undergo spontaneous, rapid (3 min, 83° C), and highly stereoselective (d, l-89− 99%) radical ...
ChemInform, 2000
ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Organometallics, 2015
ABSTRACT
Tetrahedron Letters, 2010
The phenyl group incorporated into a carbon tether provides for the synthesis of 1,5-cyclodecadiy... more The phenyl group incorporated into a carbon tether provides for the synthesis of 1,5-cyclodecadiynes with 95-100% d,l-diastereoselectivity due to intrinsic conformational constraints and preorganization of the Co 2 (CO) 6 -complexed propargyl intermediates.
Organometallics, 2008
Intramolecular radical cyclizations of Co 2 (CO) 6 -complexed bis-propargyl alcohols 1-5 provide ... more Intramolecular radical cyclizations of Co 2 (CO) 6 -complexed bis-propargyl alcohols 1-5 provide an easy, two-step access to the otherwise hardly accessible d,l-and meso-3,4-diaryl-1,5-cyclodecadiynes 21-25. The acid-induced generation of bis-cations 6-10 is followed by reduction with a 100-fold excess of zinc, generating key reactive intermediates, i.e. the cobalt-complexed bis-propargyl radicals 11-15. The substitution pattern (0-, 4-, 3,4-, 3,4,5-) and the nature of aromatic substituents (H, i-Pr, OMe) are found essential both to the diastereoselectivity of the processswith d,l:meso ratios varying from 54:46 to 80:20sand the isolability of individual stereoisomers. In particular, an accumulation of methoxy groups on the periphery of the aromatic rings facilitates separation in both intra-and intermolecular reactions. The observed disparity in the level of diastereoselection in intra-and intermolecular reactions is accounted for on the basis of conformational analysis, calculation data for cobalt-complexed propargyl radicals, and the concept of a CH/π coordination. The new knowledge thus acquired has a predicting power, allowing future substrates to be designed, both topologically and stereoelectronically, in a manner favoring either d,l or meso diastereomers.
Organometallics, 2012
A novel method for the low-temperature generation of Co2 (CO) 6-complexed propargyl radicals is d... more 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 ...
Organic Letters, 2003
[reaction: see text] The spontaneous generation and stereoselective coupling of Co(2)(CO)(6)-comp... more [reaction: see text] The spontaneous generation and stereoselective coupling of Co(2)(CO)(6)-complexed propargyl radicals have been discovered. One- and two-step complementary methods (Method A: (1) HBF(4); (2) CH(2)Cl(2), 20 degrees C; Method B: Tf(2)O, CH(2)Cl(2), 20 degrees C) provided an easy access to synthetically useful d,l-3,4-diaryl-1,5-alkadiynes (de 74-98%).
Chemistry of Heterocyclic Compounds, 1998
Upon reaction of nitrogen-containing heterocyclic aldehydes with 3-cyano-4,5,5-trimethyl-2(5H)-fu... more Upon reaction of nitrogen-containing heterocyclic aldehydes with 3-cyano-4,5,5-trimethyl-2(5H)-furanone and 3-cyano-4,6,6-trimethyl-2-(5,6-dihydro)pyrone, products of crotonic condensation and compounds of the Michael adduct type are formed.
Chemistry of Heterocyclic Compounds, 1988
The regiochemistry of the reaction of 1,2-and 1-substituted derivatives of l-buten-3-yne and its ... more The regiochemistry of the reaction of 1,2-and 1-substituted derivatives of l-buten-3-yne and its 4-and 2,4-substituted derivatives of the isoprenoid type with acetoacetic ester and acetylacetone in the presence of the manganese(III) acetate-~opper(II) acetate oxidative system was studied. Derivatives of 4,5-dihydrofuran, furan, and hexahydrobenzofuran were obtained.
Journal of Organometallic Chemistry, 2003
Last decade, the inhibitors of microtubule assembly have become a hot commodity on the pharmaceut... more Last decade, the inhibitors of microtubule assembly have become a hot commodity on the pharmaceutical market. They are best represented by an antimitotic agent colchicine 1, a, b and c, alkaloids vinblastine b and 2 [2] and vincristine [3], an antitumor agent taxol b, 2 and 4 2, 4, a and b, and methyl ...
Inorganica Chimica Acta, 2000
Alternative methods for stereoselective synthesis of the chiral racemic manganese(II) glycolate h... more Alternative methods for stereoselective synthesis of the chiral racemic manganese(II) glycolate have been developed. Its geometry is proven to be independent of the nature of the starting material (Mn(Gly)3 and Mn(OAc)3) and reaction conditions (temperature, solvent). The single-crystal X-ray analysis shows that a chiral environment around the manganese atom is created by glycolate units lying in the perpendicular planes and
Heterocyclic Communications, 2000
ABSTRACT Condensation of Gewald’s thiophenes substituted with a dimethylaminomethyleneamino group... more ABSTRACT Condensation of Gewald’s thiophenes substituted with a dimethylaminomethyleneamino group at position 2 with primary amines yields 5/6-aryl-thieno[2,3-d]pyrimidin-4-ones with variable substituents at the N3 position.
European Journal of Medicinal Chemistry, 1999
A new series of unsaturated γ-and δ-lactones with pyridyl, quinolyl and nitrophenyl substituents ... more A new series of unsaturated γ-and δ-lactones with pyridyl, quinolyl and nitrophenyl substituents (9, 10) have been synthesized by the condensation of unsaturated methyl lactones with heteryl aldehyde or nitrobenzaldehyde in the base-catalysed aldol reaction. ...
Dalton Transactions, 2013
Applicability of the term &am... more Applicability of the term "free radical" to organometallic radicals was studied by using the stereoselectivity of radical C-C bond formation as a diagnostic tool. Based on diastereoselectivity data, it was concluded that the reduction of π-bonded, Co2(CO)6-complexed propargyl cations with heterogeneous reducing agents (Zn, Mg) generates "free radicals", while homogeneous reductants (Cp2Co, Na-Ph2CO) produce "sequestered radicals", presumably associated with reductant-derived oxidized species. The latter are comparable in molecular volume to the requisite radical species, thus restricting the motion and conformational freedoms of converging, transition metal-complexed propargyl radicals. Diastereoselectivity of intermolecular reactions is determined to be much less sensitive toward temperature variation (Δde = 6-22%) than in intramolecular radical cyclizations (Δde = 106%).
Organic Letters, 2002
The relative stabilities of thymidine-3',5'-dipho... more The relative stabilities of thymidine-3',5'-diphosphoric acid (1) derived isomeric cations and radicals were calculated and key geometric parameters were thoroughly analyzed. The most probable sites of a hydride-ion (1', 2', 5-Me) and H-atom (4', 5', 5-Me) abstraction were identified, thus allowing prediction of the regioselectivity of potential damage to the deoxyribose ring and thymine moiety caused by carcinogenic agents of electrophilic and radical nature. [structure: see text]
ChemInform, 1998
Reaction of Heterocyclic Aldehydes with Methyl Derivatives of Unsaturated γ-and δ-Lactones.
Organometallics, 2009
Under neutral conditions, Co2 (CO) 6-complexed propargyl methyl ethers, upon treatment with trifl... more Under neutral conditions, Co2 (CO) 6-complexed propargyl methyl ethers, upon treatment with triflic anhydride, can be converted to the respective propargyl cations, which undergo spontaneous, rapid (3 min, 83° C), and highly stereoselective (d, l-89− 99%) radical ...
ChemInform, 2000
ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Organometallics, 2015
ABSTRACT
Tetrahedron Letters, 2010
The phenyl group incorporated into a carbon tether provides for the synthesis of 1,5-cyclodecadiy... more The phenyl group incorporated into a carbon tether provides for the synthesis of 1,5-cyclodecadiynes with 95-100% d,l-diastereoselectivity due to intrinsic conformational constraints and preorganization of the Co 2 (CO) 6 -complexed propargyl intermediates.
Organometallics, 2008
Intramolecular radical cyclizations of Co 2 (CO) 6 -complexed bis-propargyl alcohols 1-5 provide ... more Intramolecular radical cyclizations of Co 2 (CO) 6 -complexed bis-propargyl alcohols 1-5 provide an easy, two-step access to the otherwise hardly accessible d,l-and meso-3,4-diaryl-1,5-cyclodecadiynes 21-25. The acid-induced generation of bis-cations 6-10 is followed by reduction with a 100-fold excess of zinc, generating key reactive intermediates, i.e. the cobalt-complexed bis-propargyl radicals 11-15. The substitution pattern (0-, 4-, 3,4-, 3,4,5-) and the nature of aromatic substituents (H, i-Pr, OMe) are found essential both to the diastereoselectivity of the processswith d,l:meso ratios varying from 54:46 to 80:20sand the isolability of individual stereoisomers. In particular, an accumulation of methoxy groups on the periphery of the aromatic rings facilitates separation in both intra-and intermolecular reactions. The observed disparity in the level of diastereoselection in intra-and intermolecular reactions is accounted for on the basis of conformational analysis, calculation data for cobalt-complexed propargyl radicals, and the concept of a CH/π coordination. The new knowledge thus acquired has a predicting power, allowing future substrates to be designed, both topologically and stereoelectronically, in a manner favoring either d,l or meso diastereomers.
Organometallics, 2012
A novel method for the low-temperature generation of Co2 (CO) 6-complexed propargyl radicals is d... more 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 ...
Organic Letters, 2003
[reaction: see text] The spontaneous generation and stereoselective coupling of Co(2)(CO)(6)-comp... more [reaction: see text] The spontaneous generation and stereoselective coupling of Co(2)(CO)(6)-complexed propargyl radicals have been discovered. One- and two-step complementary methods (Method A: (1) HBF(4); (2) CH(2)Cl(2), 20 degrees C; Method B: Tf(2)O, CH(2)Cl(2), 20 degrees C) provided an easy access to synthetically useful d,l-3,4-diaryl-1,5-alkadiynes (de 74-98%).
Chemistry of Heterocyclic Compounds, 1998
Upon reaction of nitrogen-containing heterocyclic aldehydes with 3-cyano-4,5,5-trimethyl-2(5H)-fu... more Upon reaction of nitrogen-containing heterocyclic aldehydes with 3-cyano-4,5,5-trimethyl-2(5H)-furanone and 3-cyano-4,6,6-trimethyl-2-(5,6-dihydro)pyrone, products of crotonic condensation and compounds of the Michael adduct type are formed.
Chemistry of Heterocyclic Compounds, 1988
The regiochemistry of the reaction of 1,2-and 1-substituted derivatives of l-buten-3-yne and its ... more The regiochemistry of the reaction of 1,2-and 1-substituted derivatives of l-buten-3-yne and its 4-and 2,4-substituted derivatives of the isoprenoid type with acetoacetic ester and acetylacetone in the presence of the manganese(III) acetate-~opper(II) acetate oxidative system was studied. Derivatives of 4,5-dihydrofuran, furan, and hexahydrobenzofuran were obtained.
Journal of Organometallic Chemistry, 2003
Last decade, the inhibitors of microtubule assembly have become a hot commodity on the pharmaceut... more Last decade, the inhibitors of microtubule assembly have become a hot commodity on the pharmaceutical market. They are best represented by an antimitotic agent colchicine 1, a, b and c, alkaloids vinblastine b and 2 [2] and vincristine [3], an antitumor agent taxol b, 2 and 4 2, 4, a and b, and methyl ...
Inorganica Chimica Acta, 2000
Alternative methods for stereoselective synthesis of the chiral racemic manganese(II) glycolate h... more Alternative methods for stereoselective synthesis of the chiral racemic manganese(II) glycolate have been developed. Its geometry is proven to be independent of the nature of the starting material (Mn(Gly)3 and Mn(OAc)3) and reaction conditions (temperature, solvent). The single-crystal X-ray analysis shows that a chiral environment around the manganese atom is created by glycolate units lying in the perpendicular planes and
Heterocyclic Communications, 2000
ABSTRACT Condensation of Gewald’s thiophenes substituted with a dimethylaminomethyleneamino group... more ABSTRACT Condensation of Gewald’s thiophenes substituted with a dimethylaminomethyleneamino group at position 2 with primary amines yields 5/6-aryl-thieno[2,3-d]pyrimidin-4-ones with variable substituents at the N3 position.
European Journal of Medicinal Chemistry, 1999
A new series of unsaturated γ-and δ-lactones with pyridyl, quinolyl and nitrophenyl substituents ... more A new series of unsaturated γ-and δ-lactones with pyridyl, quinolyl and nitrophenyl substituents (9, 10) have been synthesized by the condensation of unsaturated methyl lactones with heteryl aldehyde or nitrobenzaldehyde in the base-catalysed aldol reaction. ...
Dalton Transactions, 2013
Applicability of the term &am... more Applicability of the term "free radical" to organometallic radicals was studied by using the stereoselectivity of radical C-C bond formation as a diagnostic tool. Based on diastereoselectivity data, it was concluded that the reduction of π-bonded, Co2(CO)6-complexed propargyl cations with heterogeneous reducing agents (Zn, Mg) generates "free radicals", while homogeneous reductants (Cp2Co, Na-Ph2CO) produce "sequestered radicals", presumably associated with reductant-derived oxidized species. The latter are comparable in molecular volume to the requisite radical species, thus restricting the motion and conformational freedoms of converging, transition metal-complexed propargyl radicals. Diastereoselectivity of intermolecular reactions is determined to be much less sensitive toward temperature variation (Δde = 6-22%) than in intramolecular radical cyclizations (Δde = 106%).