Recent Advances in Kinetic Resolution of Tertiary Alcohols

Isothiourea-Catalysed Acylative Kinetic Resolution of Tertiary Pyrazolone Alcohols

The development of methods for the selective acylative kinetic resolution (KR) of tertiary alcohols is a recognised synthetic challenge with relatively few successful substrate classes reported to date. In this manuscript, a highly enantioselective isothiourea-catalysed acylative KR of tertiary pyrazolone alcohols is reported. The scope and limitations of this methodology have been developed, with high selectivity observed across a broad range of substrate derivatives incorporating varying substitution at N(2)-, C(4)- and C(5)-, as well as bicyclic constraints within the pyrazolone scaffold (30 examples, selectivity factors (s) typically >100) at generally low catalyst loadings (1 mol %). The application of this KR method to tertiary alcohols derived directly from a natural product (geraniol), alongside pharmaceutically relevant drug compounds (indomethacin, gemfibrozil and probenecid), with high efficiency (s >100) is also described. The KR process is readily amenable to scale up using bench grade solvents and reagents, with effective resolution on a 50 g (0.22 mol) scale demonstrated. The key structural motif leading to excellent selectivity in this KR process has been probed through computation, with an NC=O⋅⋅⋅isothiouronium interaction from substrate to acylated catalyst observed within the favoured transition state. Similarly, the effect of C(5)-aryl substitution that leads to reduced experimental selectivity is probed, with a competitive π-isothiouronium interaction identified as leading to reduced selectivity.

Kinetic Resolution of Sulfoximines via Asymmetric Organocatalyzed Formation of Benzothiadiazine-1-oxides

A catalytic kinetic resolution of sulfoximines has been developed through chiral phosphoric acid-catalyzed intramolecular dehydrative cyclizations. A variety of racemic sulfoximines bearing an ortho-amidophenyl moiety underwent asymmetric dehydrative cyclizations using this method, yielding both the recovered sulfoximines and benzothiadiazine-1-oxide products with good to high enantioselectivities (with s-factor up to 61). The diverse derivatizations of the chiral products into a wide range of S-stereogenic center-containing S,N-heterocycles have demonstrated the value of this method.

Enantioselective rhodium-catalyzed addition of arylboronic acids to N-heteroaryl ketones: synthesis of α-hydroxy acids

The enantioselective addition of arylboronic acids to N-heteroaryl ketones provides a convenient access to chiral α-heteroaryl tertiary alcohols, yet addition reactions of this type have been challenging due to catalyst deactivation. In this report, an efficient rhodium-catalyzed addition of arylboronic acids to N-heteroaryl ketones is established, affording a variety of valuable α-heteroaryl alcohols with excellent functional group compatibility. The employment of the WingPhos ligand containing two anthryl groups is crucial for this transformation. In particular, a range of chiral benzoxazolyl-substituted tertiary alcohols were formed with excellent ee values and yields by employing a Rh loading as low as 0.3 mol%, which can serve as a practical protocol to furnish a series of chiral α-hydroxy acids after hydrolysis.