Ligand, solvent, and deuterium isotope effects in Mn(III)-based oxidative free-radical cyclizations
摘要:
Oxidation of beta-keto ester 1 with Mn(Pic)3 and Cu(OAc)2 affords bicycloalkane 8, not the expected alkene 7, which is formed in high yield with Mn(OAc)3 and Cu(OAc)2. A series of control experiments established that the most likely explanation for this observation is that Mn(PiC)2, but not Mn(OAC)2, reacts with the bicyclic radical 5 more rapidly than Cu(OAc)2 does. These studies also indicate the potential for improved yields from oxidative free-radical cyclization of deuterated substrates. For instance, reaction of beta-keto ester 1-d with 2 equiv of Mn(OAc)3 and no Cu(OAC)2 affords 65% of 8, whereas beta-keto ester 1 provides only 22% of 8 under the same conditions. Large kinetic isotope effects change the nature of the termination step and prevent the formation of acyclic radical 3 by intermolecular hydrogen transfer. Solvent and ligand effects on the oxidation of beta-keto ester 1, malonate 14, and acetylenic beta-keto ester 25 are described.
Cerium (IV) ammonium nitrate promoted oxidative cyclization of dimethyl 4-pentenylmalonate
作者:Enrico Baciocchi、Anna Belli Paolobelli、Renzo Ruzziconi
DOI:10.1016/s0040-4020(01)81235-7
日期:1992.1
CAN promoted oxidative cyclization of dimethyl 4-pentenylmalonate has been investigated in MeOH and in AcOH. The product distribution and the regioselectivity of the reaction (5-exo/6-endo ratio) appear to be very sensitive to the reaction conditions as well as the presence and the nature of copper salts, which can also be exploited from the synthetic point of view.
Solvent effects on manganese(III)-based oxidative free-radical cyclizations: ethanol and acetic acid
作者:Barry B. Snider、John E. Merritt、Mark A. Dombroski、Brad O. Buckman
DOI:10.1021/jo00019a014
日期:1991.9
Ethanol complements the typical solvent, acetic acid, for Mn(III)-based oxidative free-radical cyclizations. Cyclization of enol ether 1c to give gibberellic acid intermediate 6c is successful in ethanol, but not in acetic acid. Ethanol acts as a reducing agent for primary radicals, converting 13 and 33 to alkanes 17 and 32. Acetylenes can be used as substrates since the vinyl radicals 24 and 25 are reduced by ethanol to alkenes 26-28. The 1-hydroxyethyl radical obtained from ethanol is oxidized to acetaldehyde by Mn(III). The effect of solvent on the oxidative cyclization of unsaturated beta-keto esters 35 and 48 was examined. A higher percentage of 5-exo product is obtained in ethanol. The primary cyclopentanemethyl radicals 40 and 53 are oxidized mainly to alkenes 43 and 57 in ethanol and mainly to the alcohols 42 and 55 and lactones 41 and 58 in acetic acid.
Curran, Dennis P.; Morgan, Tina M.; Eric Schwartz, Journal of the American Chemical Society, 1991, vol. 113, # 17, p. 6607 - 6617
作者:Curran, Dennis P.、Morgan, Tina M.、Eric Schwartz、Snider, Barry B.、Dombroski, Mark A.
DOI:——
日期:——
Ligand, solvent, and deuterium isotope effects in Mn(III)-based oxidative free-radical cyclizations
作者:Barry B. Snider、Bridget A. McCarthy
DOI:10.1021/jo00075a015
日期:1993.11
Oxidation of beta-keto ester 1 with Mn(Pic)3 and Cu(OAc)2 affords bicycloalkane 8, not the expected alkene 7, which is formed in high yield with Mn(OAc)3 and Cu(OAc)2. A series of control experiments established that the most likely explanation for this observation is that Mn(PiC)2, but not Mn(OAC)2, reacts with the bicyclic radical 5 more rapidly than Cu(OAc)2 does. These studies also indicate the potential for improved yields from oxidative free-radical cyclization of deuterated substrates. For instance, reaction of beta-keto ester 1-d with 2 equiv of Mn(OAc)3 and no Cu(OAC)2 affords 65% of 8, whereas beta-keto ester 1 provides only 22% of 8 under the same conditions. Large kinetic isotope effects change the nature of the termination step and prevent the formation of acyclic radical 3 by intermolecular hydrogen transfer. Solvent and ligand effects on the oxidation of beta-keto ester 1, malonate 14, and acetylenic beta-keto ester 25 are described.