The Experts below are selected from a list of 954 Experts worldwide ranked by ideXlab platform
Joseph M. O'connor - One of the best experts on this subject based on the ideXlab platform.
-
Stereoselective Formation of η6-Arene Ruthenium(II) Complexes via Metal-Triggered Bergman and Hopf Cycloaromatizations
Organometallics, 2017Co-Authors: David M. Hitt, Stephen K. Cope, Ryan L. Holland, Kim K. Baldridge, Joseph M. O'connorAbstract:A stereoselective metal-mediated Cycloaromatization of chiral conjugated dienynes and enediynes is described. For dienyne Cycloaromatization, placement of the carbon stereocenter in the allylic position gives the highest diastereomeric ratios (dr). The observed stereoselectivity depends on the steric bulk of the alkyne substituent, as replacing a propargylic methyl for trimethylsilyl increases the dr from 56:44 to 80:20. For both enediyne and dienyne substrates, [(η5-C5Me5)Ru(NCMe)3]PF6 exhibits greater diastereoselectivity than does [(η5-C5H5)Ru(NCMe)3]PF6. For the same chiral enediyne substrate, [(η5-C5Me5)Ru(NCMe)3]PF6 generates a 4:1 ratio of diastereomeric arene products, whereas both [(η5-C5Me4CF3)Ru(NCMe)3]PF6 and [(η5-C5H5)Ru(NCMe)3]PF6 generate a 1:1 product mixture, indicative of a significant electronic influence of the ancillary ligand on diastereoselectivity. X-ray structure determination of several isolated ruthenium arene diastereomers confirms the assigned relative stereochemistry for the ...
-
Photoactivated Transition-Metal Triggers for Ambient Temperature Enediyne and Dienyne Cyclization: Ruthenium-η6-Naphthalene Complexes
Organometallics, 2017Co-Authors: Pengjin Qin, Stephen K. Cope, Han Steger, Kate M. Veccharelli, Ryan L. Holland, David M. Hitt, Curtis E. Moore, Kim K. Baldridge, Joseph M. O'connorAbstract:A persistent challenge confronting potential applications of the Bergman Cycloaromatization reaction is the development of methods for spatiotemporal control of diradical formation. Photochemical variants (photo-Bergman Cycloaromatizations) have thus far met with limited success, failing completely in the case of acyclic enediynes. Here we describe the development of efficient photoactivated transition-metal complexes that allow for spatiotemporal control of enediyne Cycloaromatization at ambient temperatures. This strategy relies on air- and moisture-stable ruthenium naphthalene complexes that undergo photochemical dissociation of the naphthalene ligand, thereby generating coordination sites for enediyne binding and Cycloaromatization. The same ruthenium naphthalene complexes also trigger dienyne cyclization under photochemical conditions.
-
A transition-metal-catalyzed enediyne Cycloaromatization.
Journal of the American Chemical Society, 2005Co-Authors: Joseph M. O'connor, Seth J. Friese, Betsy L. RodgersAbstract:The pentamethylcyclopentadienyl iron cation, generated from [(eta5-C5Me5)Fe(NCMe)3]PF6, triggers the room temperature Cycloaromatization of acyclic and alicyclic enediynes, in the presence of either 1,4-cyclohexadiene or terpinene as the hydrogen-atom donor, to give metal-arene products in good to excellent yields. Photolysis of the metal-arene complexes liberates the arene from the metal in excellent yield. The first demonstration of a transition-metal-catalyzed Cycloaromatization of conjugated enediynes has been achieved under photochemical conditions utilizing either [(eta5-C5Me5)Fe(NCMe)3]PF6 or [(eta5-C5Me5)Fe(eta6-1,2-(Prn)2C6H4)]PF6 as the catalyst precursor. The use of a metal and light has led to a convenient method for Cycloaromatization of a trans-enediyne.
-
Ruthenium-Mediated Cycloaromatization of Acyclic Enediynes and Dienynes at Ambient Temperature
Journal of the American Chemical Society, 2002Co-Authors: Joseph M. O'connor, Seth J. Friese, Mark S. TichenorAbstract:The ruthenium(II) cation, [Cp*Ru(NCMe)3]OTf (4), triggers the Bergman Cycloaromatization of acyclic endiynes at room temperature in THF solvent. Treatment of 1,2-di(1-alkynynyl)cyclopentenes (13-Me...
David M. Hitt - One of the best experts on this subject based on the ideXlab platform.
-
Stereoselective Formation of η6-Arene Ruthenium(II) Complexes via Metal-Triggered Bergman and Hopf Cycloaromatizations
Organometallics, 2017Co-Authors: David M. Hitt, Stephen K. Cope, Ryan L. Holland, Kim K. Baldridge, Joseph M. O'connorAbstract:A stereoselective metal-mediated Cycloaromatization of chiral conjugated dienynes and enediynes is described. For dienyne Cycloaromatization, placement of the carbon stereocenter in the allylic position gives the highest diastereomeric ratios (dr). The observed stereoselectivity depends on the steric bulk of the alkyne substituent, as replacing a propargylic methyl for trimethylsilyl increases the dr from 56:44 to 80:20. For both enediyne and dienyne substrates, [(η5-C5Me5)Ru(NCMe)3]PF6 exhibits greater diastereoselectivity than does [(η5-C5H5)Ru(NCMe)3]PF6. For the same chiral enediyne substrate, [(η5-C5Me5)Ru(NCMe)3]PF6 generates a 4:1 ratio of diastereomeric arene products, whereas both [(η5-C5Me4CF3)Ru(NCMe)3]PF6 and [(η5-C5H5)Ru(NCMe)3]PF6 generate a 1:1 product mixture, indicative of a significant electronic influence of the ancillary ligand on diastereoselectivity. X-ray structure determination of several isolated ruthenium arene diastereomers confirms the assigned relative stereochemistry for the ...
-
Photoactivated Transition-Metal Triggers for Ambient Temperature Enediyne and Dienyne Cyclization: Ruthenium-η6-Naphthalene Complexes
Organometallics, 2017Co-Authors: Pengjin Qin, Stephen K. Cope, Han Steger, Kate M. Veccharelli, Ryan L. Holland, David M. Hitt, Curtis E. Moore, Kim K. Baldridge, Joseph M. O'connorAbstract:A persistent challenge confronting potential applications of the Bergman Cycloaromatization reaction is the development of methods for spatiotemporal control of diradical formation. Photochemical variants (photo-Bergman Cycloaromatizations) have thus far met with limited success, failing completely in the case of acyclic enediynes. Here we describe the development of efficient photoactivated transition-metal complexes that allow for spatiotemporal control of enediyne Cycloaromatization at ambient temperatures. This strategy relies on air- and moisture-stable ruthenium naphthalene complexes that undergo photochemical dissociation of the naphthalene ligand, thereby generating coordination sites for enediyne binding and Cycloaromatization. The same ruthenium naphthalene complexes also trigger dienyne cyclization under photochemical conditions.
-
Photoactivated Transition-Metal Triggers for Ambient Temperature Enediyne and Dienyne Cyclization: Ruthenium‑η6‑Naphthalene Complexes
2017Co-Authors: Pengjin Qin, Stephen K. Cope, Han Steger, Kate M. Veccharelli, Ryan L. Holland, David M. Hitt, Curtis E. Moore, Kim K. Baldridge, Joseph M. O’connorAbstract:A persistent challenge confronting potential applications of the Bergman Cycloaromatization reaction is the development of methods for spatiotemporal control of diradical formation. Photochemical variants (photo-Bergman Cycloaromatizations) have thus far met with limited success, failing completely in the case of acyclic enediynes. Here we describe the development of efficient photoactivated transition-metal complexes that allow for spatiotemporal control of enediyne Cycloaromatization at ambient temperatures. This strategy relies on air- and moisture-stable ruthenium naphthalene complexes that undergo photochemical dissociation of the naphthalene ligand, thereby generating coordination sites for enediyne binding and Cycloaromatization. The same ruthenium naphthalene complexes also trigger dienyne cyclization under photochemical conditions
-
Investigations into novel modes of reactivity and stereoselectivity for the Cycloaromatization of conjugated enediynes and dienynes
2011Co-Authors: David M. HittAbstract:This work begins with a review of practical Cycloaromatization methodologies utilizing 1,3-dien-5-yne subunits. As a valuable addition to this body of literature, an ambient temperature dienyne Cycloaromatization pathway resulting from the formal CH activation of an allylic methyl group and subsequent alkyne 1,2-insertion triggered by cationic cyclopentadienyl ruthenium complexes (CpRu) has been discovered. This cyclization route is fundamentally different to previous studies with CpRu that resulted in the formal Hopf product and the new reactivity appears to be correlated with the bulk of the alkyne substituent. Mild levels of catalysis and selectivity have been observed for cis-1-allylic substituted dienynes, although trans-allylic dienynes were also found to be viable substrates for the stoichiometric reaction. Three transient ruthenium-dienyne complexes have been identified from the reaction of a TMS substituted dienyne, one of which is derived from the trans-1-allylic dienyne and the other two appear to be in equilibrium by ligand exchange as supported by VT NMR studies. Kinetic investigations have ruled out metal [eta]²-alkyne coordination as the reaction-triggering event as previously proposed in similar transformations. Two reaction pathways currently being considered are a [1,7]-hydrogen shift mechanism and a metal C-H insertion mechanism. In continuation of previously described metal-triggered Cycloaromatizations of dienynes and enediynes, we have investigated in situ stereoselective [eta]⁶-complexation of the products from these reactions by use of chiral substrates. Use of allylic or propargylic stereocenters led to diastereomeric ratios (d.r.) as high as 8:2. The highest stereoselectivities were found by use of a Cp* versus a Cp ligand and the relative stereochemistry for the major and minor products for both reactions were found to be consistent by X-ray structure characterization. Arene binding experiments have ruled out a mechanism in which the selective binding step occurs by complexation of the free arene. Finally we have uncovered a mode of Cycloaromatization for enediynes unrelated to the Bergman mode. The reaction occurs predominately in CDCl3 and is promoted by 1,4-cyclohexadiene and HCl. Intermediacy of a cis,cisyne is suspected and the current mechanistic hypothesis involves a cascade of pericyclic reactions leading to product initiated by a [1,7]-hydrogen shift from the dienyne
Bin Wang - One of the best experts on this subject based on the ideXlab platform.
-
A practical synthesis of β-carbolines by tetra-n-butylammonium bromide (TBAB)-mediated Cycloaromatization reaction of aldehydes with tryptophan derivatives
Chinese Chemical Letters, 2019Co-Authors: Zhen Wang, Yao Yao, Ya-kai Zhang, Xuefeng Xiao, Bin WangAbstract:Abstract A mild and efficient nBu4NBr-mediated oxidative Cycloaromatization to prepare β-carbolines from readily available tryptophans and aldehydes is described. The reaction is practical and allows the synthesis of β-carbolines on gram-scale. Some of products crystallized from the reaction mixture and were easily removed by filtration, obviating the need for chromatographic separation.
-
N-Bromosuccinimide-Induced C–H Bond Functionalization: An Intramolecular Cycloaromatization of Electron Withdrawing Group Substituted 1-Biphenyl-2-ylethanone for the Synthesis of 10-Phenanthrenol
Organic letters, 2018Co-Authors: Ya-ting Jiang, Ya-kai Zhang, Bin WangAbstract:An NBS-induced intramolecular Cycloaromatization for the synthesis of 10-phenanthrenols from electron-withdrawing group substituted 1-biphenyl-2-ylethanones is described. The in situ generated bromide was designed to act as an initiator for the radical C–H bond activation. An oxidative cross-dehydrogenative coupling reaction of a highly active C–H bond with an inert C–H bond readily occurs under mild conditions without the need for transition metals or strong oxidants.
-
n bromosuccinimide induced c h bond functionalization an intramolecular Cycloaromatization of electron withdrawing group substituted 1 biphenyl 2 ylethanone for the synthesis of 10 phenanthrenol
Organic Letters, 2018Co-Authors: Ya-ting Jiang, Ya-kai Zhang, Bin WangAbstract:An NBS-induced intramolecular Cycloaromatization for the synthesis of 10-phenanthrenols from electron-withdrawing group substituted 1-biphenyl-2-ylethanones is described. The in situ generated bromide was designed to act as an initiator for the radical C–H bond activation. An oxidative cross-dehydrogenative coupling reaction of a highly active C–H bond with an inert C–H bond readily occurs under mild conditions without the need for transition metals or strong oxidants.
-
n bromosuccinimide nbs catalyzed c h bond functionalization an annulation of alkynes with electron withdrawing group ewg substituted acetyl indoles for the synthesis of carbazoles
Organic Letters, 2017Co-Authors: Han Wang, Zhen Wang, Yilong Wang, Ruirui Zhou, Siyao Yin, Xu Yan, Bin WangAbstract:An N-bromosuccinimide-catalyzed intermolecular annulation of acetyl indoles with alkynes was developed, allowing for regioselective formation of valuable carbazoles through direct C–H bond functionalization. The readily available catalyst, wide substrate scope, gram scale synthesis, and mild conditions make this method practical. Mechanistic investigations indicate that the bromination of acetyl indole takes place to generate a bromide intermediate, followed by coupling with an alkyne and intramolecular Cycloaromatization to furnish carbazole products.
-
N‑Bromosuccinimide (NBS)-Catalyzed C–H Bond Functionalization: An Annulation of Alkynes with Electron Withdrawing Group (EWG)-Substituted Acetyl Indoles for the Synthesis of Carbazoles
2017Co-Authors: Han Wang, Zhen Wang, Yilong Wang, Ruirui Zhou, Siyao Yin, Xu Yan, Bin WangAbstract:An N-bromosuccinimide-catalyzed intermolecular annulation of acetyl indoles with alkynes was developed, allowing for regioselective formation of valuable carbazoles through direct C–H bond functionalization. The readily available catalyst, wide substrate scope, gram scale synthesis, and mild conditions make this method practical. Mechanistic investigations indicate that the bromination of acetyl indole takes place to generate a bromide intermediate, followed by coupling with an alkyne and intramolecular Cycloaromatization to furnish carbazole products
Ryan L. Holland - One of the best experts on this subject based on the ideXlab platform.
-
Stereoselective Formation of η6-Arene Ruthenium(II) Complexes via Metal-Triggered Bergman and Hopf Cycloaromatizations
Organometallics, 2017Co-Authors: David M. Hitt, Stephen K. Cope, Ryan L. Holland, Kim K. Baldridge, Joseph M. O'connorAbstract:A stereoselective metal-mediated Cycloaromatization of chiral conjugated dienynes and enediynes is described. For dienyne Cycloaromatization, placement of the carbon stereocenter in the allylic position gives the highest diastereomeric ratios (dr). The observed stereoselectivity depends on the steric bulk of the alkyne substituent, as replacing a propargylic methyl for trimethylsilyl increases the dr from 56:44 to 80:20. For both enediyne and dienyne substrates, [(η5-C5Me5)Ru(NCMe)3]PF6 exhibits greater diastereoselectivity than does [(η5-C5H5)Ru(NCMe)3]PF6. For the same chiral enediyne substrate, [(η5-C5Me5)Ru(NCMe)3]PF6 generates a 4:1 ratio of diastereomeric arene products, whereas both [(η5-C5Me4CF3)Ru(NCMe)3]PF6 and [(η5-C5H5)Ru(NCMe)3]PF6 generate a 1:1 product mixture, indicative of a significant electronic influence of the ancillary ligand on diastereoselectivity. X-ray structure determination of several isolated ruthenium arene diastereomers confirms the assigned relative stereochemistry for the ...
-
Photoactivated Transition-Metal Triggers for Ambient Temperature Enediyne and Dienyne Cyclization: Ruthenium-η6-Naphthalene Complexes
Organometallics, 2017Co-Authors: Pengjin Qin, Stephen K. Cope, Han Steger, Kate M. Veccharelli, Ryan L. Holland, David M. Hitt, Curtis E. Moore, Kim K. Baldridge, Joseph M. O'connorAbstract:A persistent challenge confronting potential applications of the Bergman Cycloaromatization reaction is the development of methods for spatiotemporal control of diradical formation. Photochemical variants (photo-Bergman Cycloaromatizations) have thus far met with limited success, failing completely in the case of acyclic enediynes. Here we describe the development of efficient photoactivated transition-metal complexes that allow for spatiotemporal control of enediyne Cycloaromatization at ambient temperatures. This strategy relies on air- and moisture-stable ruthenium naphthalene complexes that undergo photochemical dissociation of the naphthalene ligand, thereby generating coordination sites for enediyne binding and Cycloaromatization. The same ruthenium naphthalene complexes also trigger dienyne cyclization under photochemical conditions.
-
Photoactivated Transition-Metal Triggers for Ambient Temperature Enediyne and Dienyne Cyclization: Ruthenium‑η6‑Naphthalene Complexes
2017Co-Authors: Pengjin Qin, Stephen K. Cope, Han Steger, Kate M. Veccharelli, Ryan L. Holland, David M. Hitt, Curtis E. Moore, Kim K. Baldridge, Joseph M. O’connorAbstract:A persistent challenge confronting potential applications of the Bergman Cycloaromatization reaction is the development of methods for spatiotemporal control of diradical formation. Photochemical variants (photo-Bergman Cycloaromatizations) have thus far met with limited success, failing completely in the case of acyclic enediynes. Here we describe the development of efficient photoactivated transition-metal complexes that allow for spatiotemporal control of enediyne Cycloaromatization at ambient temperatures. This strategy relies on air- and moisture-stable ruthenium naphthalene complexes that undergo photochemical dissociation of the naphthalene ligand, thereby generating coordination sites for enediyne binding and Cycloaromatization. The same ruthenium naphthalene complexes also trigger dienyne cyclization under photochemical conditions
-
Stereoselective Formation of η6‑Arene Ruthenium(II) Complexes via Metal-Triggered Bergman and Hopf Cycloaromatizations
2017Co-Authors: David M. Hitt, Stephen K. Cope, Ryan L. Holland, Kim K. Baldridge, Joseph M. O’connorAbstract:A stereoselective metal-mediated Cycloaromatization of chiral conjugated dienynes and enediynes is described. For dienyne Cycloaromatization, placement of the carbon stereocenter in the allylic position gives the highest diastereomeric ratios (dr). The observed stereoselectivity depends on the steric bulk of the alkyne substituent, as replacing a propargylic methyl for trimethylsilyl increases the dr from 56:44 to 80:20. For both enediyne and dienyne substrates, [(η5-C5Me5)Ru(NCMe)3]PF6 exhibits greater diastereoselectivity than does [(η5-C5H5)Ru(NCMe)3]PF6. For the same chiral enediyne substrate, [(η5-C5Me5)Ru(NCMe)3]PF6 generates a 4:1 ratio of diastereomeric arene products, whereas both [(η5-C5Me4CF3)Ru(NCMe)3]PF6 and [(η5-C5H5)Ru(NCMe)3]PF6 generate a 1:1 product mixture, indicative of a significant electronic influence of the ancillary ligand on diastereoselectivity. X-ray structure determination of several isolated ruthenium arene diastereomers confirms the assigned relative stereochemistry for the major and minor stereoisomeric metal arene products. Arene-binding experiments demonstrate that the observed stereoselectivity does not involve complexation of free arene by ruthenium
Kim K. Baldridge - One of the best experts on this subject based on the ideXlab platform.
-
Stereoselective Formation of η6-Arene Ruthenium(II) Complexes via Metal-Triggered Bergman and Hopf Cycloaromatizations
Organometallics, 2017Co-Authors: David M. Hitt, Stephen K. Cope, Ryan L. Holland, Kim K. Baldridge, Joseph M. O'connorAbstract:A stereoselective metal-mediated Cycloaromatization of chiral conjugated dienynes and enediynes is described. For dienyne Cycloaromatization, placement of the carbon stereocenter in the allylic position gives the highest diastereomeric ratios (dr). The observed stereoselectivity depends on the steric bulk of the alkyne substituent, as replacing a propargylic methyl for trimethylsilyl increases the dr from 56:44 to 80:20. For both enediyne and dienyne substrates, [(η5-C5Me5)Ru(NCMe)3]PF6 exhibits greater diastereoselectivity than does [(η5-C5H5)Ru(NCMe)3]PF6. For the same chiral enediyne substrate, [(η5-C5Me5)Ru(NCMe)3]PF6 generates a 4:1 ratio of diastereomeric arene products, whereas both [(η5-C5Me4CF3)Ru(NCMe)3]PF6 and [(η5-C5H5)Ru(NCMe)3]PF6 generate a 1:1 product mixture, indicative of a significant electronic influence of the ancillary ligand on diastereoselectivity. X-ray structure determination of several isolated ruthenium arene diastereomers confirms the assigned relative stereochemistry for the ...
-
Photoactivated Transition-Metal Triggers for Ambient Temperature Enediyne and Dienyne Cyclization: Ruthenium-η6-Naphthalene Complexes
Organometallics, 2017Co-Authors: Pengjin Qin, Stephen K. Cope, Han Steger, Kate M. Veccharelli, Ryan L. Holland, David M. Hitt, Curtis E. Moore, Kim K. Baldridge, Joseph M. O'connorAbstract:A persistent challenge confronting potential applications of the Bergman Cycloaromatization reaction is the development of methods for spatiotemporal control of diradical formation. Photochemical variants (photo-Bergman Cycloaromatizations) have thus far met with limited success, failing completely in the case of acyclic enediynes. Here we describe the development of efficient photoactivated transition-metal complexes that allow for spatiotemporal control of enediyne Cycloaromatization at ambient temperatures. This strategy relies on air- and moisture-stable ruthenium naphthalene complexes that undergo photochemical dissociation of the naphthalene ligand, thereby generating coordination sites for enediyne binding and Cycloaromatization. The same ruthenium naphthalene complexes also trigger dienyne cyclization under photochemical conditions.
-
Photoactivated Transition-Metal Triggers for Ambient Temperature Enediyne and Dienyne Cyclization: Ruthenium‑η6‑Naphthalene Complexes
2017Co-Authors: Pengjin Qin, Stephen K. Cope, Han Steger, Kate M. Veccharelli, Ryan L. Holland, David M. Hitt, Curtis E. Moore, Kim K. Baldridge, Joseph M. O’connorAbstract:A persistent challenge confronting potential applications of the Bergman Cycloaromatization reaction is the development of methods for spatiotemporal control of diradical formation. Photochemical variants (photo-Bergman Cycloaromatizations) have thus far met with limited success, failing completely in the case of acyclic enediynes. Here we describe the development of efficient photoactivated transition-metal complexes that allow for spatiotemporal control of enediyne Cycloaromatization at ambient temperatures. This strategy relies on air- and moisture-stable ruthenium naphthalene complexes that undergo photochemical dissociation of the naphthalene ligand, thereby generating coordination sites for enediyne binding and Cycloaromatization. The same ruthenium naphthalene complexes also trigger dienyne cyclization under photochemical conditions
-
Stereoselective Formation of η6‑Arene Ruthenium(II) Complexes via Metal-Triggered Bergman and Hopf Cycloaromatizations
2017Co-Authors: David M. Hitt, Stephen K. Cope, Ryan L. Holland, Kim K. Baldridge, Joseph M. O’connorAbstract:A stereoselective metal-mediated Cycloaromatization of chiral conjugated dienynes and enediynes is described. For dienyne Cycloaromatization, placement of the carbon stereocenter in the allylic position gives the highest diastereomeric ratios (dr). The observed stereoselectivity depends on the steric bulk of the alkyne substituent, as replacing a propargylic methyl for trimethylsilyl increases the dr from 56:44 to 80:20. For both enediyne and dienyne substrates, [(η5-C5Me5)Ru(NCMe)3]PF6 exhibits greater diastereoselectivity than does [(η5-C5H5)Ru(NCMe)3]PF6. For the same chiral enediyne substrate, [(η5-C5Me5)Ru(NCMe)3]PF6 generates a 4:1 ratio of diastereomeric arene products, whereas both [(η5-C5Me4CF3)Ru(NCMe)3]PF6 and [(η5-C5H5)Ru(NCMe)3]PF6 generate a 1:1 product mixture, indicative of a significant electronic influence of the ancillary ligand on diastereoselectivity. X-ray structure determination of several isolated ruthenium arene diastereomers confirms the assigned relative stereochemistry for the major and minor stereoisomeric metal arene products. Arene-binding experiments demonstrate that the observed stereoselectivity does not involve complexation of free arene by ruthenium
