TBADT-Mediated Photocatalytic Stereoselective Radical Alkylation of Chiral N-Sulfinyl Imines: Towards Efficient Synthesis of Diverse Chiral Amines.

Herein we describe a sustainable and efficient photocatalytic method for the stereoselective radical alkylation of chiral sulfinyl imines. By employing readily available non-prefunctionalized radical precursors and the cost-effective TBADT as a direct HAT photocatalyst, we successfully obtain diverse chiral amines with high yields and excellent diastereoselectivity under mild conditions. This method provides an efficient approach for accessing a diverse array of medicinally relevant compounds, including both natural and synthetic α-amino acids, aryl ethyl amines, and other structural motifs commonly found in approved pharmaceuticals and natural product.

Access to N-Fused Quinazolinones by Radical-Promoted Cascade Annulations of Alkenyl N-Cyanamides with Aromatic Aldehydes.

A cascade radical cyclization of alkenyl N-cyanamides with aromatic aldehydes has been achieved for an expeditious synthesis of keto-methylated dihydropyrrolo-quinazolinones. Benzoyl radicals, generated from aryl aldehydes in the presence of di-tert-butyl peroxide (DTBP), promoted the domino annulations leading to distinctive functionalized quinazolinones in good yields. In addition, the robustness of the present protocol is validated by employing heterocyclic and natural product-based aldehydes.

Photocatalytic Asymmetric Acyl Radical Truce Smiles Rearrangement for the Synthesis of Enantioenriched α-Aryl Amides.

The radical Truce-Smiles rearrangement is a straightforward strategy for incorporating aryl groups into organic molecules for which asymmetric processes remains rare. By employing a readily available and non-expensive chiral auxiliary, we developed a highly efficient asymmetric photocatalytic acyl and alkyl radical Truce-Smiles rearrangement of α-substituted acrylamides using tetrabutylammonium decatungstate (TBADT) as a hydrogen atom-transfer photocatalyst, along with aldehydes or C-H containing precursors. The rearranged products exhibited excellent diastereoselectivities (7:1 to >98:2 d.r.) and chiral auxiliary was easily removed. Mechanistic studies allowed understanding the transformation in which density functional theory (DFT) calculations provided insights into the stereochemistry-determining step.

Enantioselective and Regiodivergent Synthesis of Dihydro-1,2-oxazines from Triene-Carbamates via Chiral Phosphoric Acid-Catalysis.

Conjugated trienes are fascinating building blocks for the rapid construction of complex polycyclic compounds. However, limited success has been achieved due to the challenging regioselectivity control. Herein, we report an enantio- and diastereoselective process allowing to regioselectively control the functionalization of NH-triene-carbamates. Synthesis of chiral cis-3,6-dihydro-2H-1,2-oxazines is achieved by a chiral phosphoric acid catalyzed Nitroso-Diels-Alder cycloaddition involving [(1E,3E,5E)-hexa-1,3,5-trien-1-yl]carbamates. Moreover, modular access to three different regioisomers with excellent diastereoselectivities and high to excellent enantioselectivities is obtained by a careful choice of the reaction conditions. A computational study reveals that the regioselectivity is influenced by the steric demand of the substituents at the 6-position of the triene, as well as noncovalent interactions between the two cycloaddition partners. Utility of each regioisomeric cycloadduct is highlighted by a variety of synthetic transformations.

Enantioselective and Diastereodivergent Synthesis of Spiroindolenines via Chiral Phosphoric Acid-Catalyzed Cycloaddition.

A diastereodivergent and enantioselective synthesis of chiral spirocyclohexyl-indolenines with four contiguous stereogenic centers is achieved by a chiral phosphoric acid-catalyzed cycloaddition of 2-susbtituted 3-indolylmethanols with 1,3-dienecarbamates. Modular access to two different diastereoisomers with high enantioselectivities was obtained by careful choice of reaction conditions. Their functional group manipulation provides an efficient access to enantioenriched spirocyclohexyl-indolines and -oxindoles. The origins of this stereocontrol have been identified using DFT calculations, which reveal an unexpected mechanism compared to our previous work dealing with enecarbamates.

Tritylium assisted iodine catalysis for the synthesis of unsymmetrical triarylmethanes.

The combined Lewis acid catalytic system, generated from molecular iodine and tritylium tetrafluoroborate effectively catalyzed the Friedel-Crafts (FC) arylation of diarylmethyl sulfides providing an efficient access to various unsymmetrical triarylmethanes. The addition of tritylium and iodine created a more active catalytic system to promote the cleavage of sulfidic C-S bonds.

Enantioselective Redox-Divergent Chiral Phosphoric Acid Catalyzed Quinone Diels-Alder Reactions.

An efficient enantioselective construction of tetrahydronaphthalene-1,4-diones as well as dihydronaphthalene-1,4-diols by a chiral phosphoric acid catalyzed quinone Diels-Alder reaction with dienecarbamates is reported. The nature of the protecting group on the diene is key to the success of achieving high enantioselectivity. The divergent "redox" selectivity is controlled by using an adequate amount of quinones. Reversible redox switching without erosion of enantioselectivity was possible from individual redox isomers.

Highly Diastereo- and Enantioselective Synthesis of Cyclohepta[b]indoles by Chiral-Phosphoric-Acid-Catalyzed (4+3) Cycloaddition.

A highly enantio- and diastereoselective formal (4+3) cycloaddition of 1,3-diene-1-carbamates with 3-indolylmethanols in the presence of a chiral phosphoric acid catalyst is reported. The approach described herein provides efficient access to 6-aminotetrahydrocyclohepta[b]indoles in good yields with mostly complete diastereoselectivity and excellent levels of enantioselectivity (>98:2 dr and up to 98 % ee). Mild reaction conditions, facile scale-up, and versatile derivatization highlight the practicality of this methodology. A mechanistic study suggests that cycloaddition occurs in a stepwise fashion, after the formation of an ion pair between the chiral catalytic phosphate and the intermediate carbocation.

Copper-Catalyzed Domino Three-Component Approach for the Assembly of 2-Aminated Benzimidazoles and Quinazolines.

A copper-promoted three-component synthesis of 2-aminobenzimidazoles (1) or of 2-aminoquinazolines (2) involving cyanamides, arylboronic acids, and amines has been developed. The operationally simple oxidative process, performed in the presence of K2CO3, a catalytic amount of CuCl2·2H2O, 2,2'-bipyridine, and an O2 atmosphere (1 atm), allows the rapid assembly of either benzimidazoles or quinazolines starting from aryl- or benzyl-substituted cyanamides, respectively. In this process, the copper promotes the formation of three bonds, two C-N bonds, and an additional bond resulting from C-H functionalization event.

Enantioselective synthesis of putative lipiarmycin aglycon related to fidaxomicin/tiacumicin†B.

An enantioselective synthesis of a putative lipiarmycin aglycon was accomplished and features: 1) Brown's enantioselective alkoxyallylboration and allylation of aldehydes, 2) chain elongation by iterative Horner-Wadsworth-Emmons olefination, 3) Evans' aldol reaction and 4) an ene-diene ring-closing metathesis. A neighboring-group-assisted chemoselective reductive desilylation was uncovered in this study and was instrumental to the realization of the present synthesis.

Palladium-catalyzed through-space C(sp(3))-H and C(sp(2))-H bond activation by 1,4-palladium migration: efficient synthesis of [3,4]-fused oxindoles.

Palladium two step: Linear anilides were converted into the title compounds in good to excellent yields through a palladium-catalyzed domino carbopalladation/1,4-palladium shift sequence. The C(sp(3) )-H activation involves a seven-membered palladacycle, and is chemoselective in the presence of competitive C(sp(2) )H bonds. DMA=N,N-dimethylacetamide, OPiv=pivalate.

Visible-Light-Driven Decarboxylative Borylation: Rapid Access to α- and ß-Amino-boronamides.

In this study, we described a two-step process involving an efficient visible-light-induced decarboxylative borylation of α- and ß-amino redox-active esters with bis(catecholato)diboron, followed by transamination with 1,8-diaminonapthalene (DANH2). A series of boronamides were obtained in moderate to excellent yields in this one-pot procedure. The photochemical process proved to be very efficient even when conducted under flow conditions with shorter reaction durations and scalable synthesis of DAN boronates.

Visible-Light-Mediated Divergent and Regioselective Vicinal Difunctionalization of Styrenes with Arylazo Sulfones.

Activated by visible light, arylazo sulfones can serve as multifaceted reactants and are employed in diazenylation, sulfonylation, and arylation reactions under (photo)catalyst-free conditions. Such versatile reactivity enabled us to develop an operationally simple, regioselective, and tunable difunctionalization of styrenes with arylazo sulfones to produce α-sulfonyl arylhydrazones and 1,2-alkoxyarylated products in moderate to excellent yields. Furthermore, such difunctionalized products have been exploited as key building blocks for the synthesis of various heterocycles.

Syntheses of new chiral chimeric photo-organocatalysts.

A new family of chiral chimeric photo-organocatalysts derived from phosphoric acid were synthesized and their spectroscopic and electrochemical properties were investigated. Then, the ability of these photo-activable molecules to catalyse an asymmetric tandem electrophilic ß-amination of enecarbamates was evaluated.

Chiral Phosphoric Acid-Catalyzed Enantioselective Construction of 2,3-Disubstituted Indolines.

Highly enantio- and regioselective (3 + 2) formal cycloaddition of ß-substituted ene- and thioenecarbamates as well as cyclic enamides with quinone diimides catalyzed by a BINOL- and SPINOL-derived phosphoric acid is reported. A wide variety of 2,3-disubstituted 2-aminoindolines, including polycyclic ones, were prepared in generally high yields (up to 98%) with moderate to complete diastereoselectivities and in most cases excellent enantioselectivities (up to 99% ee).

Intramolecular Suzuki-Miyaura reaction for the total synthesis of signal peptidase inhibitors, arylomycins A(2) and B(2).

Development of the total syntheses of arylomycins A(1) and B(2) is detailed. Key features of our approach include 1) formation of 14-membered meta,meta-cyclophane by an intramolecular Suzuki-Miyaura reaction; 2) incorporation of N-Me-4-hydroxyphenylglycine into the cyclization precursor, which avoids the late-stage low-yielding N-methylation step; 3) segment coupling of a fully elaborated peptide side chain to the macrocycle, which makes the synthesis highly convergent. Overall, arylomycin A(2) was obtained in 13 steps from L-Tyr for the longest linear sequence, in 13 % overall yield. Arylomycin B(2) was synthesized in 10 steps from L-3-nitro-Tyr, in 10 % overall yield.

Ugi-post functionalization, from a single set of ugi-adducts to two distinct heterocycles by microwave-assisted palladium-catalyzed cyclizations: tuning the reaction pathways by ligand switch.

Linear amides 4, prepared in one step by the Ugi four-component reaction, were converted to 3,4-dihydroquinoxalin-3-ones (5) or to 2-(2-oxoindolin-1-yl)acetamides (6) dependent on the catalytic conditions. While microwave irradiation was found to be determinant on the reaction efficiency, the choice of ligand diverged the reaction pathways. Heating a solution of 4 in dioxane/MeCN (v/v = 85/15) under microwave irradiation conditions in the presence of Pd(dba)(2) (0.05 equiv) and Cs(2)CO(3) (2 equiv), using XPhos as a supporting ligand, afforded the 3,4-dihydroquinoxalin-3-ones (5) via an intramolecular N-arylation of the secondary amide. On the other hand, using BINAP as ligand under otherwise identical conditions, intramolecular alpha-CH arylation of tertiary amide occurred to furnish the oxindoles (6).

Chiral phosphoric acid-catalyzed enantioselective construction of structurally diverse benzothiazolopyrimidines.

A highly efficient catalytic enantioselective [4+2] cycloaddition was developed between 2-benzothiazolimines and enecarbamates. A wide range of benzothiazolopyrimidines bearing three contiguous stereogenic centers was obtained in high to excellent yields and with excellent diastereo- and enantioselectivities (d.r. > 98 : 2 and up to >99% ee). Furthermore, this chiral phosphoric acid-catalyzed strategy was scalable and enabled access to a new class of optically pure Lewis base isothiourea derivatives.

Palladium-catalyzed domino intramolecular N-arylation/intermolecular C-C bond formation for the synthesis of functionalized benzodiazepinediones.

A divergent and regiocontrolled Pd-catalyzed domino sequence involving an intramolecular N-arylation and an intermolecular Heck reaction has been developed, providing rapid access to functionalized benzodiazepine-2,5-diones 3. The starting materials were synthesized by the Ugi four-component reaction. An unprecedented X-ray structure of bispalladacycle 6 was documented.

Copper-mediated N-cyclopropylation of azoles, amides, and sulfonamides by cyclopropylboronic acid.

Reaction of azoles, amides, and sulfonamides in dichloroethane with readily available cyclopropylboronic acid in the presence of copper acetate and sodium carbonate afforded the N-cyclopropyl derivatives in good to excellent yields.