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Kinetics of H· Transfer from CpCr(CO)3H to Various Enamides: Application to Construction of Pyrrolidines
The rate constants k H (k D) have been determined at 27 °C for H· (D·) transfer from CpCr(CO)3H(D) to the CC bonds of various enamides. This process leads to the formation of α-amino radicals. Vinyl enamides with N-alkyl and N-phenyl substituents have proven to be good H· acceptors, with rate con...
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Published in: | JACS Au 2023-12, Vol.3 (12), p.3366-3373 |
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description | The rate constants k H (k D) have been determined at 27 °C for H· (D·) transfer from CpCr(CO)3H(D) to the CC bonds of various enamides. This process leads to the formation of α-amino radicals. Vinyl enamides with N-alkyl and N-phenyl substituents have proven to be good H· acceptors, with rate constants close to those of styrene and methyl methacrylate. A methyl substituent on the incipient radical site decreases k H by a factor of 4; a methyl substituent on the carbon that will receive the H· decreases k H by a factor of 380. The measured k H values indicate that these α-amino radicals can be used for the cyclization of enamides to pyrrolidines. A vanadium hydride, HV(CO)4(dppe), has proven more effective at the cyclization of enamides than Cr or Co hydridespresumably because the weakness of the V–H bond leads to faster H· transfer. The use of the vanadium hydride is operationally simple, employs mild reaction conditions, and has a broad substrate scope. Calculations have confirmed that H· transfer is the slowest step in these cyclization reactions. |
doi_str_mv | 10.1021/jacsau.3c00529 |
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This process leads to the formation of α-amino radicals. Vinyl enamides with N-alkyl and N-phenyl substituents have proven to be good H· acceptors, with rate constants close to those of styrene and methyl methacrylate. A methyl substituent on the incipient radical site decreases k H by a factor of 4; a methyl substituent on the carbon that will receive the H· decreases k H by a factor of 380. The measured k H values indicate that these α-amino radicals can be used for the cyclization of enamides to pyrrolidines. A vanadium hydride, HV(CO)4(dppe), has proven more effective at the cyclization of enamides than Cr or Co hydridespresumably because the weakness of the V–H bond leads to faster H· transfer. The use of the vanadium hydride is operationally simple, employs mild reaction conditions, and has a broad substrate scope. Calculations have confirmed that H· transfer is the slowest step in these cyclization reactions.</description><identifier>ISSN: 2691-3704</identifier><identifier>EISSN: 2691-3704</identifier><identifier>DOI: 10.1021/jacsau.3c00529</identifier><language>eng</language><publisher>American Chemical Society</publisher><ispartof>JACS Au, 2023-12, Vol.3 (12), p.3366-3373</ispartof><rights>2023 The Authors. Published by American Chemical Society</rights><rights>2023 The Authors. 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This process leads to the formation of α-amino radicals. Vinyl enamides with N-alkyl and N-phenyl substituents have proven to be good H· acceptors, with rate constants close to those of styrene and methyl methacrylate. A methyl substituent on the incipient radical site decreases k H by a factor of 4; a methyl substituent on the carbon that will receive the H· decreases k H by a factor of 380. The measured k H values indicate that these α-amino radicals can be used for the cyclization of enamides to pyrrolidines. A vanadium hydride, HV(CO)4(dppe), has proven more effective at the cyclization of enamides than Cr or Co hydridespresumably because the weakness of the V–H bond leads to faster H· transfer. The use of the vanadium hydride is operationally simple, employs mild reaction conditions, and has a broad substrate scope. 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This process leads to the formation of α-amino radicals. Vinyl enamides with N-alkyl and N-phenyl substituents have proven to be good H· acceptors, with rate constants close to those of styrene and methyl methacrylate. A methyl substituent on the incipient radical site decreases k H by a factor of 4; a methyl substituent on the carbon that will receive the H· decreases k H by a factor of 380. The measured k H values indicate that these α-amino radicals can be used for the cyclization of enamides to pyrrolidines. A vanadium hydride, HV(CO)4(dppe), has proven more effective at the cyclization of enamides than Cr or Co hydridespresumably because the weakness of the V–H bond leads to faster H· transfer. The use of the vanadium hydride is operationally simple, employs mild reaction conditions, and has a broad substrate scope. Calculations have confirmed that H· transfer is the slowest step in these cyclization reactions.</abstract><pub>American Chemical Society</pub><doi>10.1021/jacsau.3c00529</doi><tpages>8</tpages><orcidid>https://orcid.org/0000-0003-1563-9555</orcidid><orcidid>https://orcid.org/0000-0003-2255-375X</orcidid><oa>free_for_read</oa></addata></record> |
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title | Kinetics of H· Transfer from CpCr(CO)3H to Various Enamides: Application to Construction of Pyrrolidines |
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