Selective Defluorination of Trifluoromethyl Substituents by Conformationally Induced Remote Substitution.

The selective reduction of an aromatic trifluoromethyl substituent to a difluoromethyl substituent may be achieved by base-promoted elimination to form a difluoro-p-quinomethide which is trapped by an intramolecular nucleophile. High yields are obtained when the nucleophilic trap entails the conformationally favoured cyclisation of an aminoisobutyric acid (Aib) derivative. The resulting cyclised difluoromethyl-substituted arylimidazolidinone products are readily converted to versatile difluoromethyl-substituted aldehydes by reduction and hydrolysis. Defluorination is successful on a range of benzenoid (both para and ortho CF3-substituted) and heterocyclic substrates. Double defluorination may likewise be achieved sequentially, or in a single step, from an Aib dipeptide derivative.

Copper-Catalyzed C(sp3 )-Amination of Ketone-Derived Dihydroquinazolinones by Aromatization-Driven C-C Bond Scission.

Herein, we describe the development of a copper-catalyzed C(sp3 )-amination of proaromatic dihydroquinazolinones derived from ketones. The reaction is enabled by the intermediacy of open-shell species arising from homolytic C-C bond-cleavage driven by aromatization. The protocol is characterized by its operational simplicity and generality, including chemical diversification of advanced intermediates.

Dihydroquinazolinones as adaptative C(sp3) handles in arylations and alkylations via dual catalytic C-C bond-functionalization.

C-C bond forming cross-couplings are convenient technologies for the construction of functional molecules. Consequently, there is continual interest in approaches that can render traditionally inert functionality as cross-coupling partners, included in this are ketones which are widely-available commodity chemicals and easy to install synthetic handles. Herein, we describe a dual catalytic strategy that utilizes dihydroquinazolinones derived from ketone congeners as adaptative one-electron handles for forging C(sp3) architectures via α C-C cleavage with aryl and alkyl bromides. Our approach is achieved by combining the flexibility and modularity of nickel catalysis with the propensity of photoredox events for generating open-shell reaction intermediates. This method is distinguished by its wide scope and broad application profile--including chemical diversification of advanced intermediates--, providing a catalytic technique complementary to existing C(sp3) cross-coupling reactions that operates within the C-C bond-functionalization arena.

Triarylmethanes and their Medium-Ring Analogues by Unactivated Truce-Smiles Rearrangement of Benzanilides.

Intramolecular nucleophilic aromatic substitution (Truce-Smiles rearrangement) of the anions of 2-benzyl benzanilides leads to triarylmethanes in an operationally simple manner. The reaction succeeds even without electronic activation of the ring that plays the role of electrophile in the SN Ar reaction, being accelerated instead by the preferred conformation imposed by the tertiary amide tether. The amide substituent of the product may be removed or transformed into alternative functional groups. A ring-expanding variant (n to n+4) of the reaction provided a route to doubly benzo-fused medium ring lactams of 10 or 11 members. Hammett analysis returned a ρ value consistent with the operation of a partially concerted reaction mechanism.

Photocatalytic Difunctionalization of Vinyl Ureas by Radical Addition Polar Truce-Smiles Rearrangement Cascades.

We report tandem alkyl-arylations and phosphonyl-arylations of vinyl ureas by way of a photocatalytic radical-polar crossover mechanism. Addition of photoredox-generated radicals to the alkene forms a new C-C or C-P bond and generates a product radical adjacent to the urea function. Reductive termination of the photocatalytic cycle generates an anion that undergoes a polar Truce-Smiles rearrangement, forming a C-C bond. The reaction is successful with a range of α-fluorinated alkyl sodium sulfinate salts and diarylphosphine oxides as radical precursors, and the conformationally accelerated Truce-Smiles rearrangement is not restricted by the electronic nature of the migrating aromatic ring. Formally the reaction constitutes an α,ß-difuctionalisation of a carbon-carbon double bond, and proceeds under mild conditions with visible light and a readily available organic photocatalyst. The products are α,α-diaryl alkylureas typically functionalized with F or P substituents that may be readily converted into α,α-diaryl alkylamines.

Connective synthesis of 5,5-disubstituted hydantoins by tandem α-amination and α-arylation of silyl ketene acetals.

5,5-Disubstituted hydantoins, formally the cyclisation products of quaternary amino acids, were formed connectively from simple ester-derived starting materials by a one-pot tandem method. Amination of the silyl ketene acetal derivative of a methyl ester takes place by silver-catalysed addition to the N[double bond, length as m-dash]N bond of an azocarboxamide, generating a N-amino-N'-aryl urea derivative of a substituted aminoester. Treatment with a base forms an ester enolate which undergoes arylation by intramolecular migration of an aryl ring to the α-position of the ester. The product undergoes ring closure to a hydantoin, which may itself be deprotected and functionalised. Aryl migration is successful with rings of various electronic character and with esters bearing functionalised and unfunctionalised chains, and the products have features in common with several bioactive compounds.

Transition Metal Free Cycloamination of Prenyl Carbamates and Ureas Promoted by Aryldiazonium Salts.

Upon treatment with aryldiazonium salts, prenyl carbamates and ureas undergo redox-neutral azocycloamination. In general, N-aryl O-prenyl carbamates cyclize in a photocatalytic reaction with visible light and an organic dye. With electron-deficient diazonium salts, electronic matching with an electron-rich N-aryl substituent results in a reaction proceeding in the ground state, without either light or photocatalyst. Cyclic voltammetry suggests that this radical reaction is initiated by hydrogen-atom abstraction mediated by an aryl radical, followed by a radical addition cascade and proton-coupled hole propagation. The reaction proceeds at room temperature in short reaction times, and a range of functional groups is tolerated.

Discovery of Pyrazolo[1,5-a]pyrimidine B-Cell Lymphoma 6 (BCL6) Binders and Optimization to High Affinity Macrocyclic Inhibitors.

Inhibition of the protein-protein interaction between B-cell lymphoma 6 (BCL6) and corepressors has been implicated as a therapeutic target in diffuse large B-cell lymphoma (DLBCL) cancers and profiling of potent and selective BCL6 inhibitors are critical to test this hypothesis. We identified a pyrazolo[1,5-a]pyrimidine series of BCL6 binders from a fragment screen in parallel with a virtual screen. Using structure-based drug design, binding affinity was increased 100000-fold. This involved displacing crystallographic water, forming new ligand-protein interactions and a macrocyclization to favor the bioactive conformation of the ligands. Optimization for slow off-rate constant kinetics was conducted as well as improving selectivity against an off-target kinase, CK2. Potency in a cellular BCL6 assay was further optimized to afford highly selective probe molecules. Only weak antiproliferative effects were observed across a number of DLBCL lines and a multiple myeloma cell line without a clear relationship to BCL6 potency. As a result, we conclude that the BCL6 hypothesis in DLBCL cancer remains unproven.