Rapid-Injection NMR Study of Iodo- and Cyano-Gilman Reagents with 2-Cyclohexenone:  Observation of π-Complexes and Their Rates of Formation

Abstract

Rapid-injection is a very useful technique for the preparation of temperature-sensitive and air-sensitive compounds in the cold, nitrogen-filled probe of an NMR spectrometer. We have used this method to prepare solutions of pi-complexes from 2-cyclohexenone and prototypical cuprates Me2CuLi.LiI and Me2CuLi.LiCN, and we have assigned structures on the basis of 1H and 13C NMR. In each case two pi-complexes were observed, and in the former, their rates of formation were measured by rapid-injection 1H NMR and EXSY spectroscopy. These results provide insights into the normal and anomalous conjugate addition reactions of organocuprates.

Nucleophilic Additions to Alkylidene Bis(sulfoxides)—Stereoelectronic Effects in Vinyl Sulfoxides

“…[5] Pre-complexation in the addition of cuprates is widely accepted in additions to a,b-unsaturated carbonyl compounds. [24] Nevertheless, the addition of cuprates to tolyl-substituted substrates 1 proceeded antiperiplanar to the axial S=O group,…”

Recent Advances in Copper-Catalyzed Asymmetric Conjugate Addition of Grignard Reagents

“…诸多有机金属试剂对 α,β-不饱和砜的不 对称加成可用来合成这类砜 [50,51] [60,61] (Scheme 2). 首先有机铜试剂与底物的碳碳 双键(π 键)络合, 形成 π 化合物, 然后经过氧化加成, 形 成三价有机铜中间体, 最后还原消除为烯醇盐和烷基 铜. π 化合物在低温下用核磁数据可得到证实 [62] , 三价 铜中间体的存在却没有直接证据, 但得到了量子化学计 算的验证 [63] . Snyder [64] …”

Detecting Elusive Intermediates in Carbohydrate Conversion: A Dynamic Ensemble of Acyclic Glucose–Catalyst Complexes

“…In the majority of cases, NMR analysis deals with stable reaction products, studies equilibria or follows reactions in real time on the minutes to hour timescales. [18][19][20] Emerging sensitivity-improving hyperpolarization (HP) technique can enhance NMR signals by several orders of magnitude 21 and enable real-time observations of transient reaction intermediates and pre-steady state measurements for catalyzed reactions. [22][23][24] We show that HP-NMR (hyperpolarized NMR) can directly observe the formation of an ensemble of acyclic glucose intermediates in complex with the catalyst without trapping the intermediates (Figure 1 4-amino-2-methylphenyl)- [1,3,5]triazinane-2,4,6-trione was obtained from GE Healthcare (Amersham, UK).…”