Investigation of an Unusual Crystal Habit of Hydrochlorothiazide Reveals Large Polar Enantiopure Domains and a Possible Crystal Nucleation Mechanism

The observation of an unusual crystal habit in the common diuretic drug hydrochlorothiazide (HCT), and identification of its subtle conformational chirality, has stimulated a detailed investigation of its crystalline forms. Enantiomeric conformers of HCT resolve into an unusual structure of conjoined enantiomorphic twin crystals comprising enantiopure domains of opposite chirality. The purity of the domains and the chiral molecular conformation are confirmed by spatially revolved synchrotron micro‐XRD experiments and neutron diffraction, respectively. Macroscopic inversion twin symmetry observed between the crystal wings suggests a pseudoracemic structure that is not a solid solution or a layered crystal structure, but an unusual structural variant of conglomerates and racemic twins. Computed interaction energies for molecular pairs in the racemic and enantiopure polymorphs of HCT, and the observation of large opposing unit‐cell dipole moments for the enantiopure domains in these twin crystals, suggest a plausible crystal nucleation mechanism for this unusual crystal habit.     

Design,Synthesis, and Application of a Chiral Sulfinamide Phosphine Catalyst for the Enantioselective Intramolecular Rauhut–Currier Reaction

A novel class of chiral sulfinamide phosphine catalysts (Xiao‐Phos) are reported, which can be easily prepared from inexpensive commercially available starting materials. The Xiao‐Phos catalysts showed good performance in enantioselective intramolecular Rauhut–Currier reactions, generating α‐methylene‐γ‐butyrolactones in high yields with up to 99 % ee under mild conditions. Moreover, kinetic resolution and parallel kinetic resolution were also observed with the use of two different substituted racemic precursors.     

Chiral Phosphoric Acid Catalyzed Kinetic Resolution of 2-Amido Benzyl Alcohols: Asymmetric Synthesis of 4H-3,1-Benzoxazines

An efficient method for the asymmetric synthesis of 4H-3,1-benzoxazines was developed by kinetic resolution of 2-amido benzyl alcohols using chiral phosphoric acid catalyzed intramolecular cyclizations. A broad range of benzyl alcohols (both secondary and tertiary alcohols) were kinetically resolved with high selectivities, with an s factor of up to 94. Mechanistic studies were performed to elucidate the mechanism of these reactions, wherein the amide moieties reacted as the electrophiles. Gram-scale reaction and facile transformations of the chiral products demonstrate the potential of this method in asymmetric synthesis of biologically active chiral heterocycles.     

Isothiourea-Catalyzed Atropselective Acylation of Biaryl Phenols via Sequential Desymmetrization/Kinetic Resolution

Axially chiral phenols are attractive targets in organic synthesis. This motif is central to many natural products and widely used as precursors to, or directly, as chiral ligands and catalysts. Despite their utility few simple catalytic methods are available for their synthesis in high enantiopurity. Herein the atropselective acylation of a range of symmetric biaryl diols is investigated using isothiourea catalysis. Studies on a model biaryl diol substrate shows that the high product er observed in the process is a result of two successive enantioselective reactions consisting of an initial enantioselective desymmetrization coupled with a second chiroablative kinetic resolution. Extension of this process to a range of substrates, including a challenging tetraorthosubstituted biaryl diol, led to highly enantioenriched products (14 examples, up to 98:2 er), with either HyperBTM or BTM identified as the optimal catalyst depending upon the substitution pattern within the substrate. Computation has been used to understand the factors that lead to high enantiocontrol in this process, with maintenance of planarity to maximize a 1,5-S⋅⋅⋅O interaction within the key acyl ammonium intermediate identified as the major feature that determines atropselective acylation and thus product enantioselectivity.