Search for: All records

The full scope and limitations of the catalytic acylative kinetic resolution of a range of tertiary heterocyclic alcohols (78 examples,sup to >200) is reported under operationally‐simple conditions, using low loadings of a commercially available Lewis basic isothiourea catalyst, HyperBTM (generally 1 mol %). The protocol is highly effective for the kinetic resolution of 3‐substituted 3‐hydroxyoxindole and α‐substituted α‐hydroxylactam derivatives bearing up to three potential recognition motifs at the stereogenic tertiary carbinol center. The full power of this methodology has been showcased through the synthesis of highly enantioenriched biologically‐active target compounds in both enantiomeric forms. To provide further insight into the reaction mechanism, a detailed kinetic analysis of this Lewis base‐catalyzed acylation of tertiary alcohols is reported using the variable time normalization analysis (VTNA) method.

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.

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.

Two bipolar host materials3‐CBPyand4‐mCBPyare reported. These hosts are structural analogs of the common host materials CBP and mCBP wherein the phenyl rings have been replaced with pyridines. The two materials possess deep highest occupied molecular orbital (HOMO) and shallow lowest unoccupied molecular orbital (LUMO) levels along with sufficiently high energyS₁andT₁states that make them suitable hosts for yellow emitters in electroluminescent devices. Yellow‐emitting thermally activated delayed fluorescence organic light‐emitting diodes are fabricated using 2,4,6‐tris (4‐(10H‐phenoxazin‐10‐yl)phenyl)‐1,3,5‐triazine (tri‐PXZ‐TRZ) as the dopant emitter with either3‐CBPyor4‐mCBPyemployed as the host. Their device performance is compared to analogous devices using CBP and mCBP as host materials. The pyridine‐containing host devices show markedly improved external quantum efficiencies (EQE) and decreased roll‐off. The 7 wt% tri‐PXZ‐TRZ‐doped device exhibits very low turn‐on voltage (2.5 V for both3‐CBPyand4‐mCBPy) along with maximum external quantum efficiencies (EQE_max) reaching 15.6% (for3‐CBPy) and 19.4% (for4‐mCBPy). The device using4‐mCBPyalso exhibits very low efficiency roll‐off with an EQE of 16.0% at a luminance of 10 000 cd m⁻².

A combination of experimental and computational studies have identified a C=O⋅⋅⋅isothiouronium interaction as key to efficient enantiodiscrimination in the kinetic resolution of tertiary heterocyclic alcohols bearing up to three potential recognition motifs at the stereogenic tertiary carbinol center. This discrimination was exploited in the isothiourea‐catalyzed acylative kinetic resolution of tertiary heterocyclic alcohols (38 examples,s factors up to >200). The reaction proceeds at low catalyst loadings (generally 1 mol %) with either isobutyric or acetic anhydride as the acylating agent under mild conditions.

A combination of experimental and computational studies have identified a C=O⋅⋅⋅isothiouronium interaction as key to efficient enantiodiscrimination in the kinetic resolution of tertiary heterocyclic alcohols bearing up to three potential recognition motifs at the stereogenic tertiary carbinol center. This discrimination was exploited in the isothiourea‐catalyzed acylative kinetic resolution of tertiary heterocyclic alcohols (38 examples,s factors up to >200). The reaction proceeds at low catalyst loadings (generally 1 mol %) with either isobutyric or acetic anhydride as the acylating agent under mild conditions.