N-Heterocyclic carbene catalysis

C-C-Bond Formations Employing N-Heterocyclic Carbene Catalysis... 

Enders D, Niemeier O, Balensiefer T (2006c) Asymmetric intramolecular cros-sed-benzoin reactions by N-heterocyclic carbene catalysis. Angew Chem Int Ed Engl 45 1463... 

Enders D, Kallfass U (2002) An efficient nucleophilic carbene catalyst for the asymmetric benzoin condensation. Angew Chem Int Ed 41 1743-1745 Enders D, Niemeier O (2004) Thiazol-2-ylidene catalysis in intramolecular crossed aldehyde-ketone benzoin reactions. Synlett 2004 2111-2114 Enders D, Niemeier O, Balensiefer T (2006) Asymmetric intramolecular crossed-benzoin reactions by N-heterocyclic carbene catalysis. Angew Chem Int Ed 45 1463-1467... 

Total Synthesis of (—)-7-Deoxyloganin Exploiting N-Heterocyclic Carbene Catalysis with a,p-Unsaturated Enol Esters... 

Although NHC (N-heterocyclic carbene) catalysis is still underdeveloped compared to other areas of organocatalysis, the number of enantioselective methodologies regardingthe direct C—H bond functionalization of aldehydes... 

Although a large number of transformations exist for N-heterocyclic carbene catalysis, until recently there was no knowledge about their compatibility with metals as catalysts and their workability in presence of each other. ° In 2010, Scheidt et al. reported the first enantioselective cooperative catalytic system, consisting of Mg(Ot-Bu)2 and a chiral N-heterocyclic carbene, which was applied in the presence of a base, such as 1,5,7-triaza-bicyclo[4.4.0]dec-5-ene (TBD), to a diastereo- and enantioselective synthesis... 

Chiang PC, Bode JW (2011) N-mesityl substituted chiral triazoliiun salts opening a new world of N-heterocyclic carbene catalysis. TCI MAIL 149 2-17... 

N-heterocyclic carbene catalysis has become one of the major categories in orga-nocatalysis. Azolium salts are ready deprotonated by weak bases to generate a carbene, which then adds to an aldehyde to form an acyl anion equivalent, generally called the Breslow intermediate. The reactive acyl anion attacks an electrophile to promote the various transformations such as benzoin, Stetter, and redox reactions [107]. Recently, an interesting approach for NHC-catalyzed generation of an enol/enolate intermediate was reported. Enantio-enriched (i-amino acid derivatives (217) are formed by the reaction between the a-aryloxyaldehyde 214 and N-tosyl-imines (215) in the presence of phenyalanine-derived azoUum salt 216 as a pre-catalyst and aryl phenoxide as a base (Scheme 28.28) [108]. 

Scheme 43.11 Secondary amine/N-heterocyclic carbene catalysis for the synthesis of 2,4-disubstituted cyclopent-2-enones.

The combination of diphenylprolinol silyl ether catalyst 34 with a primary amine catalyst was used to promote the double a-functionalization of aldehydes [140], A combination of enamine or iminium catalysis with N-heterocyclic carbene catalysis [141] and hydrogen-bonding catalysis [142] was also developed. 

Incorporation of the new catalysis concept and N-heterocyclic carbene catalysis into multicatalytic systems emerged as a new direction to build up a complex scaffold such as those often found in natural products. Liu et al. developed an enantioselective Diels-Alder reaction via trienamine catalysis of indole-2,3-quinodimethane and activated alkenes. More recently, they combined this Diels-Alder process with N-heterocyclic carbene catalysis for the rapid generation of chiral cyclopentanone-fused tetrahydrocarbazoles with diverse substitution [30]. Mechanistically, with the... 

Nolan SP, Viciu MS (2005) The Use of N-Heterocyclic Carbenes as Ligands in Palladium Mediated Catalysis. 14 241-278... 

Glorius F (ed) (2007) N-heterocyclic carbenes in transition metal catalysis. Springer, Hamburg... 

C. S. J. Cazin (ed.), N-Heterocyclic Carbenes in Transition Metal Catalysis and Organocatalysis, Catalysis by Metal Complexes 32,... 

Gabriele B, Salerno G, Costa M (2006) Oxidative Carbonylations. 18 239-272 Gade LH, Bellemin-Laponnaz S (2006) Chiral N-Heterocyclic Carbenes as Stereodirecting Ligands in Asymmetric Catalysis. 21 117-157 Gade LH, see Kassube JK (2006) 20 61-96 Gandon V, see Aubert C (2006) 19 259-294 Garcia JI, see Fraile JM (2005) 15 149-190... 

Rogers MM, Stahl SS (2006) N-Heterocyclic Carbenes as Ligands for High-Oxidation-State Metal Complexes and Oxidation Catalysis. 21 21-46 Roland S, Mangeney P (2005) Chiral Diaminocarbene Complexes, Synthesis and Application in Asymmetric Catalysis. 15 191-229 Roll R, see Behr A (2008) 23 19-52... 

Tejel C, Ciriano MA (2007) Catalysis and Organometallic Chemistry of Rhodium and Iridium in the Oxidation of Organic Substrates. 22 97-124 Tekavec TN, Louie J (2006) Transition Metal-Catalyzed Reactions Using N-Heterocyclic Carbene Ligands (Besides Pd- and Ru-Catalyzed Reactions). 21 159-192 Tesevic V, see Gladysz JA (2008) 23 67-89... 

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