Organic Base-Facilitated Thiol-Thioalkyne Reaction with Exclusive Regio- and Stereoselectivity.

Here, we report the regiospecific hydrothiolation of electron-rich thioalkynes with exclusive stereoselectivity facilitated by an organic base, which could proceed exceedingly fast under ambient atmosphere and room temperature, affording ß trans addition products in up to nearly quantitative yields. The dual nature of the sulfur atom in attracting and donating electrons is supposed to be pivotal in determining the regio- and stereoselectivity. This system tolerates a wide range of thiols and thioalkynes and shows great potential in polymer synthesis.

Iridium-Catalyzed Synthesis of Chiral 1,2,3-Triazoles Units and Precise Construction of Stereocontrolled Oligomers.

Iridium-catalyzed azide-thioalkyne cycloaddition reaction (IrAAC) has proved to be a powerful tool for the synthesis of fully substituted 1,2,3-triazole compounds with exclusive regioselectivity. Here we report its successful use in the precise construction of stereocontrolled oligomers that have great potential in diverse applications. Starting with the azide derived from L-prolinol and different functionalized thioalkynes, chiral 1,2,3-triazole units were fabricated with high efficiency under the IrAAC condition, which were further assembled into stereocontrolled oligotriazoles through metal-free exponential growth strategies. The structure and uniformity of these oligomers were well identified by 1H NMR, size-exclusion chromatography, and mass spectrometry, the stereoregularity of which were studied through circular dichroism and circular polarized luminescence analysis.

Ir-Catalyzed Regioselective Dihydroboration of Thioalkynes toward Gem-Diboryl Thioethers.

While 1,1-diboryl (gem-diboryl) compounds are valuable synthetic building blocks, currently, related studies have mainly focused on those 1,1-diboryl alkanes without a hetero functional group in the α-position. gem-Diboryl compounds with an α-hetero substituent, though highly versatile, have been limitedly accessible and thus rarely utilized. Herein, we have developed the first α-dihydroboration of heteroalkynes leading to the efficient construction of gem-diboryl, hetero-, and tetra-substituted carbon centers. This straightforward, practical, mild, and atom-economic reaction is an attractive complement to the conventional multistep synthetic strategy relying on deprotonation of gem-diborylmethane by a strong base. Specifically, [Ir(cod)(OMe)]2 was found to be uniquely effective for this process of thioalkynes, leading to excellent α-regioselectivity when delivering the two boryl groups, which is remarkable in view of the many competitive paths including monohydroboration, 1,2-dihydroboration, dehydrodiboration, triboration, tetraboration, etc. Control experiments combined with DFT calculations suggested that this process involves two sequential hydroboration events. The second hydroboration requires a higher energy barrier due to severe steric repulsion in generating the highly congested α-sulfenyl gem-diboryl carbon center, a structural motif that was almost unknown before.

Internally Functionalized Dendrimers Based on Fully Substituted 1,2,3-Triazoles.

Being one important class in dendrimer chemistry, internally functionalized dendrimers (IFDs) are still exiguous. Here, the first construction of IFDs involving fully substituted 1,2,3-triazole rings as interior functionality carriers is demonstrated. Through divergent or convergent synthetic protocols established on the efficient iridium-catalyzed annulation of internal 1-thioalkynes with organic azides, sequence-controlled heterolayered dendrimers with different branched structures are achieved in a convenient manner. 1 H NMR, mass spectrometry, and size exclusion chromatography characterizations well identify their architecture and high purity.

Hydroboration and Diboration of Internal Alkynes under Iridium Catalysis.

Here we demonstrate the feasibility and efficiency of simple iridium-based catalytic systems in the synthesis of multisubstituted alkenyl boronates from internal alkynes with high selectivities. A variety of alkynes were smoothly decorated with HBpin under a mild [Ir(cod)Cl]2/dppm/acetone condition to afford trisubstituted alkenyl boronic esters with up to >99:1 regioselectivity. The diboration reaction could effectively occur in the presence of [Ir(cod)Cl]2/DCM. Plausible mechanisms were provided to illustrate these two catalytic processes, in which the intrinsic functional group of the alkyne was supposed to be important in facilitating these reactions as well as the regioselectivity.

Iridium-catalyzed regioselective hydrosilylation of internal alkynes facilitated by directing and steric effects.

Here we reported the iridium-catalyzed hydrosilylation of internal alkynes under simple and mild conditions. The intrinsic functional groups of alkyne substrates were disclosed to be crucial in facilitating both the hydrosilylation process and related regioselectivity owing to their coordination capability towards the iridium catalyst. Utilization of the steric trimethylsilyl-protected trihydroxysilane proved to be another critical factor in ensuring the efficient proceeding of this process.

Easily Functionalized and Readable Sequence-Defined Polytriazoles.

Developing sequence-defined skeletons that could be conveniently characterized and functionalized with diverse side groups is attractive but challenging. Here we report one novel sequence-defined polytriazole structure bearing side groups at its triazole rings. Its construction was facilely accessed by the iterative employments of azidation and iridium-catalyzed cycloaddition of azide with internal 1-thioalkyne (IrAAC) in solution phase. The easy preparation of 1-thioalkyne monomers and the excellent tolerance of IrAAC enable the introduction of diverse functional side chains to this architecture. The obtained sequence was effectively characterized by tandem mass spectrometry owing to the efficient fractures of both of the Csp3-S and Csp3-N bonds in its backbone, indicating its potential utilization in high-capacity digital polymer developments. Further successful application of this structure in building monodisperse macromolecules exhibiting aggregation-induced emission (AIE) characteristics demonstrates its expected application in functional material fabrications.

Construction of sequence-defined polytriazoles by IrAAC and CuAAC reactions.

Here we report the first synthesis of sequence-defined polytriazoles, in which different side groups are sequentially anchored to the C-5 position of 1,2,3-triazole rings. By using efficient synthetic strategies based on IrAAC and CuAAC, different monodispersed polytriazoles with up to ∼5.3 kDa and 31-mer were constructed. Structural characterization via NMR, SEC, MALDI-TOF-MS, tandem MS and FTICR-MS evidenced the formation of polytriazoles with the desired specified sequences and exact chain lengths.

One simple Ir/hydrosilane catalytic system for chemoselective isomerization of 2-substituted allylic ethers.

Here, we describe one simple Ir/hydrosilane catalytic system for chemoselective isomerization of 2-substituted allylic ethers. This facile strategy shows high efficiency towards a variety of substrates, including derivatives from bioactive molecules. The substituent at the α position of the olefins is supposed to be critical in retarding the alkene hydrosilylation process and leading the reaction to go through the isomerization pathway.

Ru-Catalyzed Migratory Geminal Semihydrogenation of Internal Alkynes to Terminal Olefins.

Semihydrogenation of alkynes to alkenes represents a fundamentally useful transformation. In addition to the well-known cis- and trans-semihydrogenation, herein a geminal semihydrogenation of internal alkynes featuring 1,2-migration is described, which provides new access to the useful terminal vinylsilanes. This process also presents a new mode of reactivity of silyl alkynes. With the proper choice of the cationic [CpRu(MeCN)3]PF6 catalyst and a suitable silyl group, both aryl- and alkyl-substituted silyl alkynes can participate in this highly efficient gem-selective process. Furthermore, dedicated condition optimization also allowed switching of selectivity from gem to trans by using a combination of parameters, including the suitable silyl group, additive, and H2 pressure. A systematic DFT study on the reaction mechanism revealed that the formation of the gem-H2 Ru-carbene might be the key intermediate in both gem- and trans-addition reactions, rather than the Ru-vinylidene intermediate. The DFT results were further supported by carefully designed control experiments. This uncommon gem-addition combined with 1,2-silyl migration in the metal-carbene intermediate should open up a new synthetic avenue for alkyne transformations.

Iridium-Catalyzed Hydrosilylation of Unactivated Alkenes: Scope and Application to Late-Stage Functionalization.

Highly efficient and general Ir-catalyzed hydrosilylation of unactivated alkenes with excellent anti-Markovnikov regioselectivity was described. A broad scope of hydrosilylated products were synthesized economically and conveniently from commercially or naturally available compounds, which provides versatile valuable precursors for organic and medicinal studies.

Construction of highly sterically hindered 1,1-disilylated terminal alkenes.

One direct and efficient procedure for the synthesis of 1,1-disilylated terminal alkenes is demonstrated in this paper. To overcome and rationally utilize the steric hindrance of silyl units, the cationic ruthenium catalyst [CpRu(MeCN)3]+ was found to be effective for Markovnikov hydrosilylation of 1-silyl terminal alkynes with high yields and excellent regioselectivity. Dissimilarities between alkyl and alkoxy silyl units lead to versatile product derivatizations toward a variety of useful building blocks.

Investigations on Gold-Catalyzed Thioalkyne Activation Toward Facile Synthesis of Ketene Dithioacetals.

Nucleophilic addition to thioalkynes was investigated under various catalytic conditions with gold(I) complexes being identified as the optimal catalysts. Structural evaluation of the product revealed an unexpected cis-addition, arising from a gold-associated thioketene intermediate. Based on this interesting mechanistic insight, a gold(I)-catalyzed thioether addition to thioalkynes was developed as a novel approach to prepare ketene dithioacetals with good yields and high efficiency.

Ir-Catalyzed Regio- and Stereoselective Hydrosilylation of Internal Thioalkynes: A Combined Experimental and Computational Study.

Iridium complexes are known catalysts for a range of silylation reactions. However, the exploitation for selective hydrosilylation of unsymmetrical internal alkynes has been limitedly known. Described here is a new example of this type. Specifically, [(cod)IrCl]2 catalyzes the efficient and mild hydrosilylation of thioalkynes by various silanes with excellent regio- and stereoselectivity. DFT studies suggested a new mechanism involving Ir(I) hydride as the key intermediate.

Triazole-gold promoted intermolecular propargyl alcohol addition to alkyne: the reaction cascade toward substituted allenes.

Gold-catalyzed intermolecular propargyl alcohol addition to alkyne was achieved. The reaction of propargyl alcohol with a typical gold catalyst gave the hydration product almost exclusively. The triazole gold catalyst (TA-Au) successfully prevented the hydration, giving the vinyl ether followed by a 3,3-rearrangement. Synthetically useful substituted allenes were formed with high efficiency, substrate tolerability and chemoselectivity. Also, more than 95% chirality transfer from propargyl alcohol to allene was obtained.

Highly Regio- and Stereoselective Hydrosilylation of Internal Thioalkynes under Mild Conditions.

A general and mild hydrosilylation of thioalkynes is described. With the cationic catalyst [Cp*Ru(MeCN)3 ](+) and the bulky silane (TMSO)3 SiH, a range of thioalkynes underwent smooth hydrosilylation at room temperature with excellent α regioselectivity and syn stereoselectivity. DFT calculations provided important insight into the mechanism, particularly the unusual syn selectivity with the [Cp*Ru(MeCN)3 ](+) catalyst. The sulfenyl group in the substrates was found to provide important chelation stabilization to direct the reaction through a new mechanistic pathway.

Iridium-catalyzed intermolecular azide-alkyne cycloaddition of internal thioalkynes under mild conditions.

An iridium-catalyzed azide-alkyne cycloaddition reaction (IrAAC) of electron-rich internal alkynes is described. It is the first efficient intermolecular AAC of internal thioalkynes. The reaction exhibits remarkable features, such as high efficiency and regioselectivity, mild reaction conditions, easy operation, and excellent compatibility with air and a broad spectrum of organic and aqueous solvents. It complements the well-known CuAAC and RuAAC click reactions.

Ligand-controlled remarkable regio- and stereodivergence in intermolecular hydrosilylation of internal alkynes: experimental and theoretical studies.

The first highly efficient ligand-controlled regio- and stereodivergent intermolecular hydrosilylations of internal alkynes have been disclosed. Cationic ruthenium complexes [Cp*Ru(MeCN)3](+) and [CpRu(MeCN)3](+) have been demonstrated to catalyze intermolecular hydrosilylations of silyl alkynes to form a range of vinyldisilanes with excellent but opposite regio- and stereoselectivity, with the former being α anti addition and the latter ß syn addition. The use of a silyl masking group not only provides sufficient steric bulk for high selectivity but also leads to versatile product derivatizations toward a variety of useful building blocks. DFT calculations suggest that the reactions proceed by a mechanism that involves oxidative hydrometalation, isomerization, and reductive silyl migration. The energetics of the transition states and intermediates varies dramatically with the catalyst ligand (Cp* and Cp). Theoretical studies combined with experimental evidence confirm that steric effect plays a critical role in governing the regio- and stereoselectivity, and the interplay between the substituent in the alkyne (e.g., silyl group) and the ligand ultimately determines the observed remarkable regio- and stereodivergence.

Copper-catalyzed direct oxidative annulation of N-iminopyridinium ylides with terminal alkynes using O2 as oxidant.

The aerobic direct dehydrogenative annulation of N-iminopyridinium ylides with terminal alkynes leading to pyrazolo[1,5-a]pyridine derivatives has been developed.

N,N-dimethylformamide: a multipurpose building block.

Often used as a common solvent for chemical reations and utilized widely in industry as a reagent, N,N-dimethylformamide (DMF) has played an important role in organic synthesis for a long time. Numerous highly useful articles and reviews discussing its utilizations have been published. With a focus on the performance of DMF as a multipurpose precursor for various units in numerous reactions, this Minireview summarizes recent developments in the employment of DMF in the fields of formylation, aminocarbonylation, amination, amidation, and cyanation, as well as its reaction with arynes.