Deng reaction

Deng reaction 985,1004 3-deoxy sugars 914 deprotonated carboxylic acid 479 deprotonations 43... 

Although acid catalysis is thought to be necessary for the Biginelli reaction, there has been a report disputing this requirement. Ranu and coworkers surveyed over 20 aldehydes and showed that excellent yields of DHPMs could be achieved at 100-105°C in 1 h in the absence of catalyst and solvent with no by-products formed. In contrast Peng and Deng reported no significant formation of DHPM 15 when a mixture of benzaldehyde (5), ethyl acetoacetate (6), and urea (3a) was heated at 100°C for 30 min. 

Esterification reactions can be catalyzed by the ionic liquid 1-butylpyridinium chloride-aluminium chloride ([BP]C1/A1C13 (X(A1C13) = 0.33) [34, 35]. Deng and coworkers found that higher yields were obtained than in similar reactions with a sulfuric acid catalyst. 

Deng and Peng have found that certain ionic liquids catalyze the Biginelli reaction [62]. Usually, this reaction is catalyzed by Lewis acids such as InCl3, [Fe(H20)6]Cl3, or BF3.0(C2H5)2, or by acid catalysts such as Nafion-H. The reaction was found to give yields in the 77-99 % range in the ionic liquids [BMIM][PF6] or [BMIM][BF4] for the examples in Scheme 5.1-34. The reaction fails if there is no ionic liquid present or in the presence of tetrabutylammonium chloride. 

Deng et al. (2004a,b) prepared the crystals of the spent obelin (W92F mutant from O. longissima) that had been luminesced with Ca2+, and successfully obtained the X-ray structure of apoobelin as an important information in elucidating the mechanism of the luminescence reaction. 

Deng, L., Ziegler, T., 1997, Theoretical Study of the Oxidation of Alcohols to Aldehyde by d° Transition-Metal-Oxo Complexes Combined Approach Based on Density Functional Theory and die Intrinsic Reaction Coordinate Method , Organometallics, 16, 716. 

Fu Q, Deng W, Saltsburg H, Flytzani-Stephanopoulos M (2005) Activity and stability of low-content gold-cerium oxide catalysts for the water-gas shift reaction. Appl Catal B 56 57-68... 

Deng, L., V. Branchadell, and T. Ziegler. 1994. Potential Energy Surface of the Gas-Phase Sn2 Reactions X + CH2X = XCH3 + X- (X = F, Cl, Br, I) A Comparative Study by Density Functional Theory and ab initio Methods. 

The precursor alloy is quenched to form small grains readily attacked by the caustic solution [31], Quenching can also enable specific intermetallic phases to be obtained, although this is less common. Yamauchi et al. [32-34] have employed a very fast quench to obtain a supersaturation of promoter species in the alloy. It is even possible to obtain an amorphous metal glass of an alloy, and Deng et al. [35] provide a review of this area, particularly with Ni, Ni-P, Ni-B, Ni-Co, and Ni-Co-B systems. The increased catalytic activity observed with these leached amorphous alloy systems can be attributed to either chemical promotion of the catalyzed reaction or an increased surface area of the leached catalyst, depending on the components present in the original alloy. Promotion with additives is considered in more detail later. 

Deng, Q., Moore, R. B. and Mauritz, K. A. 1995. Novel Nation ORMOSIL hybrids via in situ sol-gel reactions. 1. Probe of ORMOSIL phase nanostructures by infrared spectroscopy. Chemistry of Materials 7 2259-2268. 

Deng et al. (1997) studied the reaction of metallic iron powder (5 g 40 mesh) and vinyl chloride (15.0 mL) under anaerobic conditions at various temperatures. In the experiments, the vials containing the iron and vinyl chloride were placed on a roller drum set at 8 rpm. Separate reactions were performed at 4, 20, 32, and 45 °C. The major degradate produced was ethylene. Degradation followed pseudo-first-order kinetics. The rate of degradation increased as the temperature increased. Based on the estimated activation energy for vinyl chloride reduction of 40 kilojoules/mol, the investigators concluded that the overall rate of reaction was controlled at the surface rather than the solution. 

Deng and Overman [74] employed their aza-Cope rearrangement-Mannich cyclization reaction as the key step in an approach to both (+)-and (-)-preussin. 

The first organocatalyzed conjugate addition of a-substituted p-ketoester to a,P-unsaturated ketones was presented by Deng et al. [42] (Scheme 3). Although traditional Cinchona alkaloids were efficient catalysts for conjugate addition of carbon nucleophiles to nitroalkenes and sulfones, replacement of the C(9)-OH with an ester group (Q-7b) showed great improvement in stereoselectivity. The reaction is applicable to a variety of cyclic and acyclic enones (16,18). 

The efficiency with which modified Cinchona alkaloids catalyze conjugate additions of a-substituted a-cyanoacetates highlights the nitrile group s stereoselective role with the catalyst. Deng et al. [60] utilized this observation to develop a one-step construction of chiral acyclic adducts that have non-adjacent, 1,3-tertiary-quatemary stereocenters. Based on their mechanistic studies and proposed transition state model, the bifimctional nature of the quinoline C(6 )-OH Cinchona alkaloids could induce a tandem conjugate addition-protonation reaction to create the tertiary and quaternary stereocenters in an enantioselective and diastereoselective manner (Scheme 18). 

The nitroaldol reaction, particularly involving ketones has been relatively unexplored in the field of asymmetric organocatalysis. Employing cupreines and cupreidines as catalysts, Deng [63] presented an enantioselective nitroaldol reaction of a-ketoesters... 

Okamura and Nakatani [65] revealed that the cycloaddition of 3-hydroxy-2-py-rone 107 with electron deficient dienophiles such as simple a,p-unsaturated aldehydes form the endo adduct under base catalysis. The reaction proceeds under NEtj, but demonstrates superior selectivity with Cinchona alkaloids. More recently, Deng et al. [66], through use of modified Cinchona alkaloids, expanded the dienophile pool in the Diels-Alder reaction of 3-hydroxy-2-pyrone 107 with a,p-unsaturated ketones. The mechanistic insight reveals that the bifunctional Cinchona alkaloid catalyst, via multiple hydrogen bonding, raises the HOMO of the 2-pyrone while lowering the LUMO of the dienophile with simultaneous stereocontrol over the substrates (Scheme 22). 

Asides from the application of imines on conjugate addition reactions, Deng [87, 88] reported the first asymmetric chiral thiourea catalyzed Friedel-Crafts reaction of indoles with iV-tosyl imines (Scheme 35). The reaction was receptive to various aromatic, heteroaromatic, and aliphatic imines in good yield and high enantioselec-tivity (Scheme 36). 

Deng also showed that (DHQD)2AQN could catalyze the parallel KR (PKR) of a variety of monosubstituted succinic anhydrides via asymmetric alcoholysis [215]. The nature of the solvent was found to have a significant influence on the selectivity. Hence, increasing the size of the alcohol from methanol to ethanol resulted in increased levels of enantioselectivity, albeit with reduced reaction rates. In this context, 2,2,2-trifluoroethanol appeared to be the alcohol of choice as it allowed the ASD of 2-methyl succinic anhydride (58a) with a remarkable level of selectivity. Indeed, the use of (DHQD)2AQN (15 mol%) provided a mixture of two regioiso-meric hemiesters 59a and 60a in a 1 1 ratio with 93 and 80% ee respectively. 

An interesting expansion to the scope of dienes that could be adopted as partners within the Diels-Alder cycloaddition was reported by Deng (Scheme 57) [193]. Reaction of 3-hydroxypyrones 145 with a broad range of a,p-unsaturated ketones in the presence of the primary cinchona alkaloid 144 (5 mol%) provided the Diels-Alder adducts with exceptional levels of asymmetric induction (up to 99% ee). Within this report it was also shown that the related alkaloid 146 provided access to the enantiomeric adducts with similar levels of asymmetric induction. 

Peng Q, Dong Y, Deng Z, Sun X, Li Y (2001) Low temperature elemental-direct-reaction route to II-VI semiconductor nanociystalline ZnSe and CdSe. Inorg Chem 40 3840-3841... 

The Deng group identified QN-derived thiourea 121 and QD -derived thiourea 124 to be also efficient promoters of enantio- and diastereoselective Diels-Alder reactions between the 2-pyrone diene 3-hydroxypyran-2-one and the dienophiles fumaronitrile, maleonitrile as well as acrylonitrile, while various C9-hydroxy acylated and alkylated (dihydro)cupreines and (dihydro)cupreidines failed for the same reactions under identical conditions (e.g., 97% yield, 15% ee, 64 36 endoxxo) [289], Catalysts 121 and 124 (5mol% loading), however, produced the corresponding Diels-Alder adducts 1-3 with synthetically useful enantioselectivities (85-... 

C.D. Cadicamo, J. Courtieu, H. Deng, A. Meddour, D. O Hagan, Enzymatic fluorina-tion in Streptomyces cattleya takes place with an inversion of configuration consistent with an Sn2 reaction mechanism, ChemBioChem 5 (2004) 685-690. 

Deng and co-workers have also applied the cinchona derivatives to the kinetic resolution of protected a-amino acid N-carboxyanhydrides 51 [48]. A variety of alkyl and aryl-substituted amino acids may be prepared with high se-lectivities (krei=23-170, see Scheme 10). Hydrolysis of the starting material, in the presence of the product and catalyst, followed by extractive workup allows for recovery of ester, carboxylic acid, and catalyst. The catalyst may be recycled with little effect on selectivity (run 1, krei=114 run 2, krei=104). The reaction exhibits first-order dependence on methanol and catalyst and a kinetic isotope effect (A MeOH/ MeOD=l-3). The authors postulate that this is most consistent with a mechanism wherein rate-determining attack of alcohol is facilitated by (DHQD)2AQN acting as a general base. 5-Alkyl 1,3-dioxolanes 52 may also... 

---