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Metal-free organocatalysts

Keywords Cyanation, a-Cyanohydrin, a-Aminonitrile, Cyanide, HCN, TMSCN, Lewis acid, Metal-free, Organocatalyst, C=0 bond, C=N bond, Strecker, Reissert, Aldehydes, Ketones, Imines, Aldimines, Ketoimines... [Pg.117]

A procedure for alkylation of C=0 double bonds in the presence of (metal-free) organocatalysts and non-metallic nucleophiles has been reported by the Iseki group for trifluoromethylation of aldehydes and ketones [185]. On the basis of a previous study of the Olah group [186, 187] which showed the suitability of non-chiral phase-transfer catalysts for trifluoromethylation of carbonyl compounds, Iseki et al. investigated the use of N-benzylcinchonium fluoride, 182, as a chiral catalyst. The reaction has been investigated with several aldehydes and aromatic ketones. Trifluoromethyltrimethylsilane, 181, was used as nucleophile. The reaction was, typically, performed at —78 °C with a catalytic amount (10-20 mol%) of 182, followed by subsequent hydrolysis of the siloxy compound and formation of the desired alcohols of type 183 (Scheme 6.82). [Pg.205]

By contrast, metal free organocatalysts [6] can be viewed as an attractive altemative to those processes in which the metal is not vital for the key bond forming event. The advantages are obvious no metal leaching to the product, reduced toxicity, and lower cost of the catalysts and their regeneration. Therefore, the prime goal here is to develop new, robust processes that could compete with their established, metal catalyzed counterparts. [Pg.132]

A range of metal-free organocatalysts have been used to good effect in the kinetic resolution of alcohols. A number of enantiomerically pure 4-aminopyridine-based catalysts effect kinetic resolution with high S values. These include the conforma-tionallyrestricted2,3-dihydroimidazo[l,2-a]pyridine (12.98) and the atropiso-meric catalyst (12.99). N-heterocyclic carbenes also function as nucleophilic... [Pg.346]

This review will concentrate on metal-free Lewis acids, which incorporate a Lewis acidic cation or a hypervalent center. Lewis acids are considered to be species with a vacant orbital [6,7]. Nevertheless, there are two successful classes of organocatalysts, which may be referred to as Lewis acids and are presented in other chapter. The first type is the proton of a Brpnsted acid catalyst, which is the simplest Lewis acid. The enantioselectivities obtained are due to the formation of a chiral ion pair. The other type are hydrogen bond activating organocatalysts, which can be considered to be Lewis acids or pseudo-Lewis acids. [Pg.350]

A new, metal-free protocol involving (heteroaryl)oxazoline catalysts for the enantioselective reduction of aromatic ketones (up to 94% ee) and ketimines (up to 87% ee) with trichlorosilane has been developed. The reaction is characterized by an unusual, long-ranging chiral induction.The enantiodifferentiation is presumed to be aided by aromatic interactions between the catalyst and the substrate.360 Asymmetric reduction of A-arylketimines with trichlorosilane is catalysed by A-methyl-L-amino acid-derived Lewis-basic organocatalysts with high enantioselectivity (up to 92% ee) 61... [Pg.138]

Organocatalysts are inexpensive, readily available, and nontoxic. The products are free from the contamination of metals, so various highly enantioselective, metal free reactions have been developed to obtain biologically active compounds based on... [Pg.334]

More recent efforts to effect metal-free hydrogenations have fallen in the realm of organo-catalysts. For example, the hydrogenation of enones, imines, unsaturated a,P-aldehydes, and quinolines have been achieved without a metal, however, in these cases the stoichiometric source of H2 was a Hantzsch ester (Scheme 11.3) [10-14], Such a protocol can be applied to asymmetric reductions, as substituted enones can be reduced with reasonable enantiomer excesses between 73 and 91%. A variety of organocatalyst systems have been reviewed [15, 16]. [Pg.262]

The organocatalyst for this metal-free approach to ROP of cyclic monomers is a nucleophilic transesterification catalysts. The linear correlation between the molecular weight and conversion is proof for the living character of this nucleophilic... [Pg.29]

Keywords Benzyne C-H functionalization Heteroaromatic A(-oxides Metal-free reactions Nucleophilic addition Organocatalyst Radical reactions... [Pg.155]


See other pages where Metal-free organocatalysts is mentioned: [Pg.5]    [Pg.17]    [Pg.5738]    [Pg.273]    [Pg.273]    [Pg.2]    [Pg.9]    [Pg.159]    [Pg.155]    [Pg.5]    [Pg.17]    [Pg.5738]    [Pg.273]    [Pg.273]    [Pg.2]    [Pg.9]    [Pg.159]    [Pg.155]    [Pg.76]    [Pg.208]    [Pg.141]    [Pg.142]    [Pg.147]    [Pg.308]    [Pg.11]    [Pg.9]    [Pg.105]    [Pg.134]    [Pg.110]    [Pg.121]    [Pg.4]    [Pg.46]    [Pg.282]    [Pg.17]    [Pg.264]    [Pg.294]    [Pg.318]    [Pg.318]    [Pg.248]    [Pg.295]    [Pg.283]    [Pg.29]    [Pg.2]    [Pg.141]    [Pg.239]    [Pg.712]    [Pg.243]    [Pg.712]    [Pg.62]   
See also in sourсe #XX -- [ Pg.2 ]




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