Cyanations catalytic asymmetric

Sn(OTf)2 can function as a catalyst for aldol reactions, allylations, and cyanations asymmetric versions of these reactions have also been reported. Diastereoselective and enantioselective aldol reactions of aldehydes with silyl enol ethers using Sn(OTf)2 and a chiral amine have been reported (Scheme SO) 338 33 5 A proposed active complex is shown in the scheme. Catalytic asymmetric aldol reactions using Sn(OTf)2, a chiral diamine, and tin(II) oxide have been developed.340 Tin(II) oxide is assumed to prevent achiral reaction pathway by weakening the Lewis acidity of Me3SiOTf, which is formed during the reaction. 

One of the most important approaches to a-amino acids is based on the Strecker reaction. Although there are already a number of catalytic asymmetric variants, the cyanation of imines still challenges modem organic chemists. 

Spino, C. Recent developments in the catalytic asymmetric cyanation of ketimines. Angew. Chem., Int. Ed. Engl. 2004, 43, 1764-1766. 

The catalytic asymmetric cyanation of imines-the Strecker reaction-represents one of the most direct and viable methods for the asymmetric synthesis of a-amino... 

Catalytic asymmetric cyanation using 20 mol % of the complex of Ti(Oz-Pr)4 with diisoporpyl tartrate (10 Fig. 1) was reported by Oguni [42,43]. The mixture of Ti(Oi-Pr)4 and 10 (Fig. l)did not exhibit high enantioselectivity. Moreover, the selectivity and the reactivity were still low when the formed isopropyl alcho-hol was removed under reduced pressure using the freeze-dry method. High reactivity and an enantioselectivity of up to 90% were observed when the isopropyl alcohol was again added to the freeze-dried titanium complex. 

Recent developments in the catalytic asymmetric cyanation of ketimines. (c) T. Vilaivan, W. Bhanthumnauin, Y. Sritana-Anant, Curr. Org. Chem. 2005, 9, 1315-1392. Recent advances in catalytic asymmetric addition to imines and related C=N systems, (d) S. J. Connon, Angew. Chem. Int. Ed. 2008,47,1176-1178. The catalytic asymmetric Strecker reaction ketimines continue to join the fold. 

Catalytic Asymmetric Cyanation with Trimethylsilyl Cyanide as the Cyanide Source... 

Johnson s group developed a catalytic asymmetric cyanation/1,2-Brook rearrangement/C-acylation of acylsilanes with cyanoformates (Scheme 19.14). In the presence of (i ,/ )-(salen)Al 19, the corresponding cyanohydrin trimethylsilyl ethers of a-keto esters were obtained in moderate to good enantioselectivities (61-82% enantiomeric excess). Access to chiral (silyloxy)nitrile anions is facilitated by metal cyanide-promoted Brook rearrangement reaction of acylsilanes. 

Optically active cyanohydrins can be easily transformed to P-hydroxy amines, a-hydroxy and a-amino carboxylic acids, which represent versatile intermediates for the synthesis of biologically important compounds, including insecticides and medicines [189, 190]. Asymmetric cyanation of carbonyl compounds catalyzed by chiral metal complexes, particularly titanium compounds, has provided one of the most convenient protocols to the access of these type of compounds. The first example of catalytic asymmetric cyanation of aliphatic aldehydes was realized in Reetz s group using BINOL-Ti complex as the catalyst to give the cyanohydrins in up to 82% ee [104] (Scheme 14.85). 

Table 18 Catalytic asymmetric cyanation reactions of p,p-disubstituted a,p-imsaturated ketones using a chiral strontium catalyst...

Kurono N, Ohkuma T (2016) Catalytic asymmetric cyanation reactions. ACS Catal 6... 

Catalytic Asymmetric Cyanation with (R]-BINOLi/-PrOLi (10mol%) [87]... 

In addition to this, asymmetric 1,3-dipolar cyclization reactions of nitrones with olefins,40 41 catalytic enantioselective cyanation of aldehydes,42 catalytic enantioselective animation,43 and aza-Michael reactions44 have been reported, and high enantioselectivities are observed. 

Thus transition metal complexes capable of effecting cyanation reactions on aromatic nuclei under mild conditions have been discovered Cassar et al. describe such a catalytic system. The past few years have also seen the discovery of asymmetric catalysis. Asymmetric catalysts contain optically active ligands and, like enzymes, can promote catalytic reactions during which substantial levels of optical activity are introduced into the products. This volume contains examples of asymmetric hydrogenation and asymmetric hydroformylation catalysis in the papers, respectively, by Knowles et al. and Pino et al. 

Cyanation of carbonyl compounds has one of the richest histories of any transformation in the field of asymmetric catalysis, and intensive research efforts have continued unabated since the editorial deadline for the first edition of Comprehensive Asymmetric Catalysis in 1998. This chapter will summarize all efforts in this area from 1998 to date, highlighting the most important catalytic systems from a synthetic and/or mechanistic standpoint. Significant advances in both the cyanation of aldehydes (formation of secondary cyanohydrins Section 28.2.1) and the cyanation of ketones (formation of tertiary cyanohydrins Section 28.2.2) will be addressed [1,2]. 

The cyanation of imines, generally known as the Strecker reaction, has been one of the most aggressively studied transformations of asymmetric catalysis over the past several years. Very recent efforts in this area have resulted in the discovery of several highly efficient catalytic systems capable of providing a-ami-... 

The potential substrates for the Strecker reaction fall into two categories ald-imines (derived from aldehydes, for which cyanide addition results in formation of a tertiary stereocenter) and ketoimines (derived from ketones, for which addition results in a quaternary stereocenter). As in the case of carbonyl cyanation, significant differences are observed between the substrate subclasses. To date, while a few catalyst systems have been found to display broad substrate scope with respect to aldimine substrates, successful Strecker reactions of ketoimines have been reported in only two cases. As is the case for all asymmetric catalytic methodologies, the breadth of the substrate scope constitutes a crucial criterion for the application of the Strecker reaction to a previously unexplored substrate. 

Optically pure cyanohydrins serve as highly versatile synthetic building blocks [24], Much effort has, therefore, been devoted to the development of efficient catalytic systems for the enantioselective cyanation of aldehydes and ketones using HCN or trimethylsilyl cyanide (TMSCN) as a cyanide source [24], More recently, cyanoformic esters (ROC(O)CN), acetyl cyanide (CH3C(0)CN), and diethyl cyanophosphonate have also been successfully employed as cyanide sources to afford the corresponding functionalized cyanohydrins. It should be noted here that, as mentioned in Chapter 1, the cinchona alkaloid catalyzed asymmetric hydrocyanation of aldehydes discovered... 

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