Quinidine derived thiourea derivative

Ricci et al. [85] reported the use of a quinidine-derived chiral catalyst in the asymmetric addition of nitromethane to iV-Boc imine 40. At around the same time, S chans and co-workers used a dihydroquinidine-derive chiral thiourea DHQD-134 applicable to nitromethane and nitroethane 149 [86]. The application of nitroethane conveniently generates a tertiary stereogenic center in the P-nitroamine product 151. The methodology presented by Schaus is also applicable to novel... 

C9-epi-122 98% conv. (99% ee) after 30h, respectively (Figure 6.40). This structure-efficiency relationship supported the results already published by the Soos group for quinine- and quinidine-derived thioureas (Figure 6.39) [278]. C9-epimeric catalysts were found to be remarkably more efficient in terms of rate acceleration and stereoinduction than the analogs of natural cinchona alkaloid stereochemistry. This trend was also observed for the corresponding (thio)ureas derived from DHQD as shown by the experimental results in Figure 6.40 [279]. 

Later, a dramatic jump in the ee values was achieved by the same research group by introducing the thiourea moiety at the 6 -position of 44 [22]. Using 10 mol% of the quinidine-derived catalyst 46, the highly enantioselective Henry reaction between nitromethane and the aromatic aldehydes (electron-rich, electron-deficient, and... 

A highly enantioselective and regioselective allylic substitution of the BH carbonates using nitroalkanes as nucleophiles was developed by Lu and co-workers [135] in the presence of quinidine-derived thiourea catalyst 76. The nitroalkanes was added to the BH carbonates in the 3 position (as depicted in Scheme 9.36) in good yields and enantioselectivities (Scheme 9.38). 

The Michael-type 5(0) -exo-trig and 6(0)"-cxo-trig cycloetherifications of e-hydroxy-a,/3-unsaturated ketones HO(CH2) CH=CHCOR (n = 3 or 4), catalysed by the bifunctional Cinchona alkaloid-derived thioureas, such as the quinidine derivative (131), have been reported to produce the corresponding a-substituted THFs and tetrahydropyrans, respectively, with <95% ee at room temperature over 24 h at 3mol% catalyst loading. The reaction is believed to proceed via the doubly activated species (132). ... 

Addition of -naphthols to alkylideneindolenines (generated in situ from arenesul-fonylalkylindoles), catalysed by the quinidine-derived thiourea (289b), exhibited <98% ee ... 

The Soos group, in 2005, prepared the first thiourea derivatives from the cinchona alkaloids quinine QN (8S, 9R-121), dihydroquinidine DHQD (8S, 9S-122), C9-epi-QN (8S, 9P-123), and quinidine QD (SR, 9R-124) via an experimentally simple one-step protocol with epimerization at the C9-position of the alkaloid starting material (Figure 6.39) [278]. The catalytic efficiency of these new thiourea derivatives and also of unmodified QN and C9-epi-QN was evaluated in the enan-tioselective Michael addition [149-152] of nitromethane to the simple model chal-cone 1,3-diphenyl-propenone resulting in adduct 1 in Scheme 6.119. After 99h reaction time at 25 °C in toluene and at 10 mol% catalyst loading QN turned out to be a poor catalyst (4% yield/42% ee (S)-adduct) and C9-epi-QN even failed to accelerate the screening reaction. In contrast, the C9-modified cinchona alkaloid... 

Deng and coworkers also found that the bifunctional quinidine- or quinine-based thioureas 36 and 40 effectively catalyze the asymmetric Friedel-Crafts reaction of indoles with a variety of aromatic and alkyl-substituted aldimine derivatives 159. Both enantiomeric forms of the products 160 were obtained with uniformly high... 

The first organocatalyzed enolate-mediated aldol reaction of active carbonyl derivatives with unactivated ketones was reported by Zhao and co-workers [170]. In this methodology, a ketone is deprotonated by the tertiary amine in the quinidine thiourea catalyst backbone and the enolate associates closely with the catalyst through ionic interactions. This method of activation can be used in cases where... 

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