Gold(I)-catalysed direct thioetherifications using allylic alcohols: an experimental and computational study

B(C6F5)3-Catalyzed Regiodivergent Thioetherifications of Alkenes via Thiiranium Intermediates: Experimental and Computational Insights

Precise control of selective alkene functionalization is a continuing challenge in the chemical community. In this study, we develop a substitution-controlled regiodivergent thioetherification of di- or trisubstituted alkenes using 10 mol % tris(pentafluorophenyl)borane [B(C6F5)3] as a catalyst and N-thiosuccinimide as a sulfenylating reagent. This metal-free borane catalyzed C-S bond forming method is utilized for a Csp2-H sulfenylation reaction to synthesize an array of diphenylvinylsulfide derivatives with good to excellent yields (25 examples, up to 91 % yield). Some of the products exhibit aggregation-induced emission luminogen properties used in organic light-emitting diodes (OLEDs), chemical sensors, and biological imaging units. Depending upon the starting alkene, Csp3-S sulfenylation products could also be generated regioselectively. A variety of allylic thioethers from α-alkyl substituted styrenes were isolable in good yields and selectivities (14 examples, up to 67 % yield). The DFT-supported mechanistic study confirms that the reaction proceeds via a thiiranium ion intermediate, where the regioselectivity and product formation is determined by the alkene substituents which influence the activation barriers and energy profiles. Diphenylvinylsulfide derivatives can also be efficiently transformed into a range of synthetically valuable compounds, including vinyl sulfoxides, vinyl sulfones, and vinyl sulfoximines.

Recent progress in the chemistry of β-aminoketones

The current study highlighted the significance of β-aminoketones as privileged biologically active molecules, recent synthetic strategies, and synthetic applications.

Gold-catalyzed thioetherification of allyl, benzyl, and propargyl phosphates

Supported gold catalysts showed high activity for thioetherification of various phosphates. The surface of gold nanoparticles supported on ZrO2 served as a source for active cationic Au species.

K2S2O8 promoted dehydrative cross-coupling between α,α-disubstituted allylic alcohols and thiophenols/thiols

K₂S₂O₈ promoted dehydrative cross-coupling between α,α-disubstituted allylic alcohols and thiophenols/thiols is demonstrated for the first time, leading to a wide range of allyl sulfides in good to high yields.

Gold-Catalyzed Asymmetric Thioallylation of Propiolates via Charge-Induced Thio-Claisen Rearrangement

A gold(I)-catalyzed enantioselective thioallylation of propiolates with allyl sulfides is described. The key mechanistic element is a sulfonium-induced Claisen rearrangement which helps minimize the allyl dissociation and render higher enantioselectivity. This protocol features remarkable scope of the allyl moiety, allowing enantiocontrolled synthesis of all-carbon quaternary centers, and exhibits exceptional functional group compatibility with many Lewis bases and π-bonds. This intermolecular variant of Claisen rearrangement forges both C-S and C-C bonds concomitantly, providing efficient access to interesting optically active organosulfur compounds which can be transformed further through the vinyl sulfide as a functional handle. The rate of the reaction was zeroth order with respect to allyl sulfides, which suggested a reversible inhibition, providing a resting state for the catalyst. The Hammett plot displayed a correlation with σ_p values, suggesting a turnover-limiting sigmatropic rearrangement where decreased electron-density on sulfur accelerated the rearrangement.

Pyridine hydrochloride-catalyzed thiolation of alkenes: divergent synthesis of allyl and vinyl sulfides

Divergent synthesis of allyl and vinyl sulfides by a Py-HCl catalyzed tandem thiolation–elimination reaction between N-thiosuccinimides and alkenes.

Gold-Catalyzed Hydroamination of Propargylic Alcohols: Controlling Divergent Catalytic Reaction Pathways To Access 1,3-Amino Alcohols, 3-Hydroxyketones, or 3-Aminoketones

A versatile approach to the valorization of propargylic alcohols is reported, enabling controlled access to three different products from the same starting materials. First, a general method for the hydroamination of propargylic alcohols with anilines is described using gold catalysis to give 3-hydroxyimines with complete regioselectivity. These 3-hydroxyimines can be reduced to give 1,3-amino alcohols with high syn selectivity. Alternatively, by using a catalytic quantity of aniline, 3-hydroxyketones can be obtained in high yield directly from propargylic alcohols. Further manipulation of the reaction conditions enables the selective formation of 3-aminoketones via a rearrangement/hydroamination pathway. The utility of the new chemistry was exemplified by the one-pot synthesis of a selection of N-arylpyrrolidines and N-arylpiperidines. A mechanism for the hydroamination has been proposed on the basis of experimental studies and density functional theory calculations.

Synthesis of α-functionalized α-indol-3-yl carbonyls through direct SN reactions of indol-3-yl α-acyloins

A new and efficient synthesis of α-functionalized α-indol-3-yl ketones from easily available indolyl α-acyloins is reported. This process, catalyzed by Brønsted or Lewis acids, involves an uncommon direct nucleophilic substitution reaction of a secondary α-carbonyl-substituted hydroxyl group. The described methodology allows the introduction of a variety of nucleophiles such as (hetero)arenes, thiophenols, nitroanilines and 1,3-dicarbonyl derivatives. The synthesized α-indol-3-yl carbonyl compounds are important synthetic targets also useful for accessing functionalized tryptophols and furan-3-yl indoles.

Rapid Iododeboronation with and without Gold Catalysis: Application to Radiolabelling of Arenes

Radiopharmaceuticals that incorporate radioactive iodine in combination with single‐photon emission computed tomography imaging play a key role in nuclear medicine, with applications in drug development and disease diagnosis. Despite this importance, there are relatively few general methods for the incorporation of radioiodine into small molecules. This work reports a rapid air‐ and moisture‐stable ipso‐iododeboronation procedure that uses NIS in the non‐toxic, green solvent dimethyl carbonate. The fast reaction and mild conditions of the gold‐catalysed method led to the development of a highly efficient process for the radiolabelling of arenes, which constitutes the first example of an application of homogenous gold catalysis to selective radiosynthesis. This was exemplified by the efficient synthesis of radiolabelled meta‐[¹²⁵I]iodobenzylguanidine, a radiopharmaceutical that is used for the imaging and therapy of human norepinephrine transporter‐expressing tumours.

Chirality Transfer in Gold(I)-Catalysed Direct Allylic Etherifications of Unactivated Alcohols: Experimental and Computational Study

Gold(I)-catalysed direct allylic etherifications have been successfully carried out with chirality transfer to yield enantioenriched, γ-substituted secondary allylic ethers. Our investigations include a full substrate-scope screen to ascertain substituent effects on the regioselectivity, stereoselectivity and efficiency of chirality transfer, as well as control experiments to elucidate the mechanistic subtleties of the chirality-transfer process. Crucially, addition of molecular sieves was found to be necessary to ensure efficient and general chirality transfer. Computational studies suggest that the efficiency of chirality transfer is linked to the aggregation of the alcohol nucleophile around the reactive π-bound Au-allylic ether complex. With a single alcohol nucleophile, a high degree of chirality transfer is predicted. However, if three alcohols are present, alternative proton transfer chain mechanisms that erode the efficiency of chirality transfer become competitive.

Gold-Catalyzed Proto- and Deuterodeboronation

A mild gold-catalyzed protodeboronation reaction, which does not require acid or base additives and can be carried out in "green" solvents, is described. As a result, the reaction is very functional-group-tolerant, even to acid- and base-sensitive functional groups, and should allow for the boronic acid group to be used as an effective traceless directing or blocking group. The reaction has also been extended to deuterodeboronations for regiospecific ipso-deuterations of aryls and heteroaryls from the corresponding organoboronic acid. Based on density functional theory calculations, a mechanism is proposed that involves nucleophilic attack of water at boron followed by rate-limiting B-C bond cleavage and facile protonolysis of a Au-σ-phenyl intermediate.

One-Pot Synthesis of Allylic Sulfones, Ketosulfones, and Triflyl Allylic Alcohols from Domino Reactions of Allylic Alcohols with Sulfinic Acid under Metal-Free Conditions

A metal-free tandem procedure by using a sulfonylation reaction of aryl allylic alcohols followed by an iodobenzenediacetate (PIDA)-promoted oxidative functionalization has been established. Allylic sulfones, γ-ketosulfones, and triflyl allylic alcohols have been constructed in a single operation. The methodology incorporates the sulfonyl (both aryl and triflyl) functionality with a simple work-up procedure.

Dehydrative thiolation of allenols: indium vs gold catalysis

Intermolecular additions of thiols to allenols via formal S(N)2' selectivity to produce functionalized dienes are described. Although this dehydrative reaction was initially developed using gold(I) catalysis, indium(III) proves to be a far superior catalyst in terms of selectivity and substrate scope.