Abstract
BINOLs are valuable and widely used building blocks, chiral ligands, and catalysts that are effective across a remarkable range of different chemical transformations. Here we demonstrate that an ammonium salt catalyzed kinetic resolution of racemic BINOLs with benzyl tosylate proceeds with s up to 46. This is a scalable and practical process that can be applied across >30 different C 2‐ and non‐C 2‐symmetric BINOLs. Implementation of this method enables the enantioselective synthesis of a wide range of BINOL derivatives with over 99:1 e.r.
Highlights
BINOLs are valuable and widely used building blocks, chiral ligands and catalysts that are effective across a remarkable range of different chemical transformations
C2-Symmetric BINOLs are generally accessible through derivatization of enantiopure BINOL, which can be accessed by resolution[2] and from commercial sources.[3]
With a working process in hand, we examined the scope of our counterion-mediated kinetic resolution across both C2- and non C2symmetric substrates (Table 2)
Summary
Pseudomonas sp. lipoprotein lipase (Toyobo LIP-301), in the presence of isopropenyl acetate (Figure 1D).[12]. The use of benzyl iodide as the electrophile gave a broadly similar selectivity (s = 12, entry 3), but higher conversion (53%) was achieved when using benzene as the solvent (entry 4) This is a valuable observation, as temporal control of conversion is important for attaining high levels of enantioselectivity in kinetic resolutions. 7,7’dibromo derivative functions well under the optimized reaction conditions (s = 33) These positions appear to be somewhat sensitive to substitution: and are both less selective substrates than most others. Changing the aryl group as in 35-37 is well tolerated with little effect on selectivity 5,5’-substituted BINOLS are good substrates for the kinetic resolution: 38 and are successful and selective substrates but 5,5’-diphenyl substrate is significantly less selective.
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