The kinetics of the racemization of 1,3-disubstituted allenes catalyzed by (IPr)AuOTf (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidine) has been investigated. The rate of gold-catalyzed allene racemization obeyed the following second-order rate law: rate = k(rac)[allene] [Au]. An analysis of the rate of the gold-catalyzed racemization of 1-aryl-1,2-butadienes as a function of allene electron donor ability established moderate depletion of electron density on the C1 allenyl carbon atom in the rate-limiting transition state for racemization. Analysis of the temperature dependence of the rate of racemization of 1-(p-tolyl)-1,2-butadiene established the activation parameters Delta H-double dagger = 8.3 +/- 1 kcal mol(-1) and Delta S-double dagger = -28 +/- 4 eu. These observations were in accord with a mechanism for allene racemization involving turnover-limiting, intermolecular allene exchange followed by rapid allene stereomutation.
Regio- and Stereoselective Synthesis of Alkyl Allylic Ethers via Gold(I)-Catalyzed Intermolecular Hydroalkoxylation of Allenes with Alcohols
作者:Zhibin Zhang、Ross A. Widenhoefer
DOI:10.1021/ol800646h
日期:2008.5.1
carbene complex and AgOTf at roomtemperature for 1 h led to isolation of (E)-(3-phenethoxy-1-butenyl)benzene in 96% yield as a single regio- and stereoisomer. Gold(I)-catalyzed intermolecular allene hydroalkoxylation was effective for monosubsituted, 1,1- and 1,3-disubstituted, trisubstituted, and tetrasubstituted allenes and for a range of primary and secondary alcohols, methanol, phenol, and propionic
作者:Zhibin Zhang、Seong Du Lee、Aaron S. Fisher、Ross A. Widenhoefer
DOI:10.1016/j.tet.2008.10.113
日期:2009.2
A gold(I) N-heterocyclic carbene complex catalyzes the intermolecular hydration of allenes to form allylic alcohols in modest yield with selective delivery of water to the terminal carbon atoms of the allenyl moiety.
金 (I) N -杂环卡宾配合物催化丙二烯的分子间水合,以适度的产率形成烯丙醇,并选择性地将水输送到丙二烯基部分的末端碳原子。
Intermolecular Hydroamination of Allenes with <i>N</i>-Unsubstituted Carbamates Catalyzed by a Gold(I) <i>N</i>-Heterocyclic Carbene Complex
作者:Robert E. Kinder、Zhibin Zhang、Ross A. Widenhoefer
DOI:10.1021/ol8010858
日期:2008.7.17
Reaction of 2,3-pentadienyl benzoate with benzyl carbamate catalyzed by a 1:1 mixture of (NHC)AuCl and AgOTf in dioxane at 23 degrees C for 5 h led to isolation of (E)-4-(benzyloxycarbonylamino)-2-pentenyl benzoate in 84% yield as a single regio- and diastereomer. Gold(I)-catalyzed hydroamination was effective for a number of N-unsubstituted carbamates and a range of substituted allenes.