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BINOL-Al catalysed asymmetric cyclization and amplification: preparation of optically active menthol analogs

“…We carried out the cyclization in the presence of a more bulky ligand, (R,R)-9-phenanthrylTADDOL ((R)-3c). 25 The enantioselectivity of (−)-trans-2 was higher than that of (R)-3b (Table 1, entry 3). However, the reactivity of the complex with (R)-3c was much lower than that with (R)-3b.…”

“…16 896 mg, 5.32 mmol, 90%, 90% ee; [α] 20 D = +7.1 (c 0.25, THF); 1 H-NMR (500 MHz, CDCl 3 ): δ 0.94 (s, 3H, CH 3 ), 0.97 (s, 3H, CH 3 ), 1.14 (t, 1H, J = 11.7 Hz), 1.22 (td, 1H, J = 13.2, 4.7 Hz), 1. 25 Large scale procedure of synthesis of (−)-trans-2 (Table 2, entry 2) A mixture of (R)-4a (1.63 g, 6.42 mmol, 9 mol%), triethylaluminium toluene solution (1.0 mol L −1 , 3.6 mL, 5 mol%), and dichloromethane (32 mL) was added to a 200 mL reactor under a N 2 atmosphere. After stirring at r.t. for over 1 h, the solution was cooled to less than 10 °C.…”

Kinetic Rationalization of Nonlinear Effects in Asymmetric Catalysis Based on Phase Behavior

“…As an example, we studied both the equilibrium phase behavior and the dissolution kinetics of taddol derivative 5; nonlinear behavior has been reported in a variety of asymmetric reactions using this class of compounds. [25][26][27] We found that 5 forms a true racemic compound exhibiting an extremely high eutectic ee value of over 99 % ee under solidsolution equilibrium. [20] Figure 3 reveals that taddol exhibits the behavior of a kinetic conglomerate phase as it dissolves; for a 40 % ee taddol mixture, solution ee values spanning the entire range from nearly racemic to nearly enantiopure are obtained over time.…”

“…The quantitative phase behavior of most commonly employed chiral ligands remains virtually unexplored, although nonlinear effects have been reported in a number of cases that may be related to factors influenced by solidsolution phase behavior, such as the concentration and preparation of the catalyst as well as reaction protocols. [25][26][27][28][29][30] This work shows that both the sign and the magnitude of the observed nonlinear effect may depend on the kinetics of catalyst dissolution. As an example, we studied both the equilibrium phase behavior and the dissolution kinetics of taddol derivative 5; nonlinear behavior has been reported in a variety of asymmetric reactions using this class of compounds.…”

(−)-(4R,5R)-4,5-Bis[hydroxy(diphenyl)methyl]-2,2-dimethyl-1,3-dioxolane

“…26 Chiral Reagent. TADDOL has been employed as a chiral acid in the enantioselective protonation of the achiral enolate (20) (eq 9) 27. …”