Search

A metal-free dual C(sp3)-H bond functionalization of saturated cyclic ethers via photooxidative singlet oxygen-mediated ring opening and ring closing has been developed, providing a method for generating hydrobenzofurans/pyrans/dioxins. Mechanistic studies have confirmed that ring-opening intermediates were effectively generated by singlet oxygen-mediated C(sp3)-H activation and efficiently reacted with aldehydes and activated methylene compounds to form a wide array of products with high diastereoselectivities (up to >95:5 dr). This study is a rare example of α,β-dual C(sp3)-H bond functionalization of ethers.

Herein, we report the development of an efficient green procedure for synthesizing carbonyl furan derivatives by dehydrogenative coupling of furfuryl alcohol with carbonyl compounds. The reaction is performed under mild reaction conditions in the presence of

Herein, we report the Pd(0)-catalyzed intermolecular asymmetric dearomative [3 + 2] annulation of phenols with vinyl cyclopropanes via in situ generated

The catalytic dehydrogenation of alcohols is essential for the sustainable production of valuable products. This provides a new strategy for green organic synthesis in chemical industries. Herein, we describe a manganese-based catalytic system that enables the efficient synthesis of C3-alkylated indoles from benzyl alcohols and indoles via the borrowing hydrogen process. Furthermore, dehydrogenative coupling of 2-arylethanols and indoles yields C3-alkenylated indoles. Meanwhile, reacting 2-aminophenethanol instead of indoles can also obtain the corresponding indole products with high selectivity under the same conditions.

We demonstrate that α-aryl cyclic vinylogous esters are competent substrates in the direct intermolecular Pd-catalyzed asymmetric allylic alkylation, enabling a straightforward enantioselective synthesis of 6-allyl-6-aryl-3-ethoxycyclohex-2-en-1-ones, common motifs embedded in numerous structurally diverse natural products. As an initial demonstration of the utility of this protocol, the first catalytic enantioselective total synthesis of (+)-oxomaritidine and an improved five-step catalytic enantioselective synthesis of (-)-mesembrine have been completed divergently.

Chiral phosphoric acid-catalyzed biomimetic asymmetric [4 + 2] cycloaddition of ortho-alkenyl naphthols/phenols and ortho-quinone methides (o-QMs) has been demonstrated to afford various important 2,3,4-trisubstituted chromans in high yields with excellent enantio- and diastereoselectivities (up to 99% yield, 99% ee, >20:1 dr). Notably, this methodology not only enabled access to the trans-cis chiral trisubstituted chromans from 1-alkenyl 2-naphthols but also is compatible with 2-alkenyl 1-naphthols and phenols to deliver trans-trans chiral trisubstituted chromans.

A SPINOL-derived chiral phosphoric acid catalyzed asymmetric formal [2 + 3]-annulation of in situ generated alkynyl imines and 1,4-dithiane-2,5-diol has been developed to afford enantiopure α-alkynylated thiazolidones with up to 72% yield and 98.5 : 1.5 er. This tandem annulation involved a tandem S-addition of alkynyl imines/intramolecular acetalization, followed by PDC-mediated oxidation. The α-alkynylated thiazolidones could facilely afford the corresponding chiral α-alkynylated or α-alkenylated cyclic sulfoxides via further elaboration.

Direct enantioselective Michael-type Friedel–Crafts arylations and heteroarylations of s-cis 1-azadienes were achieved by applying chiral bifunctional tertiary amine-urea catalysts when using 2-naphthols as the nucleophiles, and phosphoric acid catalysts when using indoles as the nucleophiles. These two catalytic protocols efficiently enabled access to a diverse variety of important benzofuran-containing hetero-triarylmethanes in up to 98% yield and with 99.5 : 0.5 er.

N-Tosylhydrazones have had widespread application in organic synthesis for more than a half century. In most of cases, N-tosylhydrazones, as masked diazo compounds, have been generally used in a series of important carbon–carbon and carbon–heteroatom bond-forming reactions. This review provides an update on progress in diverse coupling reactions of N-tosylhydrazones since 2012. The examples selected are mainly categorized by metal-catalyzed and metal-free systems, wherein four main types of transformations including insertion, olefination, alkynylation, and cyclization are discussed for each system.1 Introduction2 Transition-Metal-Catalyzed Coupling Reactions3 Metal-Free Coupling Reactions4 Conclusion and Outlook

The direct oxidation of alcohols into carboxylic acids is an essential reaction for the synthesis of bulky and fine chemicals. Most current processes require the use of either strong and toxic oxidants or the presence of pressurized oxygen. Herein, we report a sustainable manganese-catalyzed acceptorless dehydrogenative coupling of alcohols with alkaline water to form carboxylates generating H2 as the sole by-product. This is a general applicable and efficient non-noble metal catalyzed dehydrogenative transformation of alcohols into carboxylates. The reaction proceeded selectively in the presence of a well-defined manganese pincer complex at a very low catalyst loading. A wide range of carboxylic acids (46 examples) were synthesized with high yields and excellent functional group tolerance. Mechanistic studies including control experiments, NMR spectroscopy, and X-ray crystallography identified the resting state and key intermediates in the catalytic cycle.

A novel strategy for the dearomatization of naphthols using in situ generated oxy-allyl cations is reported. Both α- and β-naphthols can work well in this process. Using this catalyst-free methodology, various structurally diverse α-quaternary center-containing 2-(2-oxocycloalkyl)cycloalkyl diketones can be efficiently accessed in good to excellent yields under mild conditions.

Herein we show the application potential of primary amine catalysts in the context of Mannich reactions of aldehydes with ketimines exemplified by isatins-derived ketimines and cyclic trifluoromethyl ketimines. Primary amine catalysts exhibit either unusual stereoselectivity or reactivity, which is not observable with secondary amine catalysts. Moreover, reversal of diastereofacial selectivity between primary and secondary amine catalysts is disclosed. These new reactions provide useful methods for the syntheses of chiral 3-substituted 3-amino-2-oxindoles and dihydroquinazolinones bearing a trifluoromethylated quaternary stereocenter. The synthetic utility of the reactions is demonstrated through the formal synthesis of AG-041R and DPC 083 and the total synthesis of (-)-psychotriasine.

Catalytic asymmetric and divergent assembly of tricyclic and tetracyclic 3,3′-pyrrolidonyl spirooxindoles was developed, involving a one-pot chiral Bronsted base catalyzed asymmetric propargylation for the synthesis of oxindole 1,6-enynes and a subsequent switchable site-selective and highly diastereoselective electrophilic iodocyclization of 1,6-enynes. In addition, antitumor properties of the newly synthesized compounds were evaluated.

of main observation and conclusion Catalytic hydrogenation of esters is essential for the sustainable production of alcohols in organic synthesis and chemical industry. Herein, we describe the first non-noble metal catalytic system that enables an efficient hydrogenation of non-activated esters to alcohols in the absence of phosphine ligands (with a maximum turnover number of 2391). The general applicability of this protocol was demonstrated by the high-yielding hydrogenation of 39 ester substrates including aromatic/aliphatic esters, lactones, polyesters and various pharmaceutical molecules.

The first highly stereoselective intermolecular catalytic asymmetric dearomatization (CADA) of α-naphthols through C–C formation and the first asymmetric allylic dearomatization of naphthols by chiral organocatalysis have been achieved. These new and complete atom-economic reactions provide enantioriched α- and β-naphthalenones bearing an all-carbon quaternary center.

Herein, we report a novel cobalt-catalyzed stereodivergent transfer hydrogenation of alkynes to Z- and E-alkenes. Effective selectivity control is achieved based on a rational catalyst design. Moreover, this mild system allows for the transfer hydrogenation of alkynes bearing a wide range of functional groups in good yields using catalyst loadings as low as 0.2 mol %. The general applicability of this procedure is highlighted by the synthesis of more than 50 alkenes with good chemo- and stereoselectivity. A preliminary mechanistic study revealed that E-alkene product was generated via sequential alkyne hydrogenation to give Z-alkene intermediate, followed by a Z to E alkene isomerization process.

Isobutanol serves as an ideal gasoline additive owing to its good compatibility with current engine technology, high energy density, and high octane number. Herein, an efficient and selective Mn-catalyzed upgrading of ethanol with methanol into isobutanol is reported. This is the first example of deoxygenative coupling of lower alcohols to isobutanol by using a homogeneous non-noble-metal catalyst. This transformation proceeded at very low catalyst loading with a high turnover number (9233) and up to 96 % isobutanol selectivity.

Biomass-derived ethanol is an important renewable feedstock. Its conversion into high-quality biofuels is a promising route to replace fossil resources. Herein, an efficient manganese-catalyzed Guerbet-type condensation reaction of ethanol to form 1-butanol was explored. This is the first example of upgrading ethanol into higher alcohols using a homogeneous non-noble-metal catalyst. This process proceeded selectively in the presence of a well-defined manganese pincer complex at the parts per million (ppm) level. The developed reaction represents a sustainable synthesis of 1-butanol with excellent turnover number (>110 000) and turnover frequency (>3000 h–1). Moreover, mechanistic studies including control experiments, NMR spectroscopy, and X-ray crystallography identified the essential role of the “N–H moiety” of the manganese catalysts and the major reaction intermediates related to the catalytic cycle.

We report the first catalytic asymmetric approach to octahydroindolones and a divergent enantioselective synthesis of perhydroindole alkaloids, as exemplified by lycorine-type Amaryllidaceae alkaloids (+)-α-lycorane and (+)-lycorine, from a common intermediate by using a highly concise route. The assembly of octahydroindolones employs a catalytic enantioselective 1,4-conjugate addition of nitro dienynes, followed by a TsOH-catalyzed cascade synthesis of highly functionalized enones, and a diastereoselective intramolecular Michael addition.

The first arylation strategy for the synthesis of enantioenriched propargylamines is disclosed. This approach, which is complementary to previous alkynylation and alkylation strategies, involves a C(sp2 )-C(sp3 ) bond formation, and is based on the first asymmetric Friedel-Crafts-type arylation reaction of C-alkynyl imines. Asymmetric Friedel-Crafts reactions with electron-deficient phenols, a longstanding unsolved challenge, have thus been realized for the first time, enabled by the combination of our recently introduced C-alkynyl N-Boc-protected N,O-acetals as electrophiles and chiral phosphoric acids as catalysts. The synthetic utility of the resulting structurally diverse and polyfunctional chiral propargylamines was demonstrated by a series of selective transformations, including controlled reduction of the alkynyl group and iterative cross-couplings.

α,β-Unsaturated ynones have historically been used as Michael acceptors in conjugate addition reactions. Herein, we have demonstrated for the first time that ynones can be harnessed as Michael donors for use in catalytic asymmetric conjugate addition reactions by strategically introducing a CO2t-Bu group as a multitasking directing group. Furthermore, this concept has enabled designer ynones as versatile synthetic equivalents of both α' anions of ynones and γ monoanions of 1,3-diketones, which are synthetically valued but difficult to generate. The first catalytic enantioselective conjugate addition of ynones as Michael donors has been realized in good yields with high enantioselectivities. A unified approach to regiospecifically and chemo- and enantioselectively access hitherto elusive γ-Michael adducts of 1,3-diketones has been achieved in a divergent manner. The strategy described here by exploring new reactivity and creating new reagents holds great potential applications in other still unsolved transformations.

Herein, we describe a selective cobalt-catalyzed chemodivergent transfer hydrogenation of nitriles to synthesize primary, secondary, and tertiary amines. The solvent effect plays a key role for the selectivity control. The general applicability of this procedure was highlighted by the synthesis of more than 70 amine products bearing various functional groups in high chemoselectivity. Moreover, this mild system achieved >2000 TONs (turnover numbers) for the transfer hydrogenation of nitriles.

A new class of chiral primary amine catalysts bearing multiple hydrogen-bonding donors have been designed and synthesized. The newly developed bifunctional organocatalysts efficiently catalyzed not only enantioselective conjugate addition of aromatic ketones to nitroolefins in good yields (up to 87%) with excellent enantioselectivities (97→99% ee) but also enantioselective conjugate addition of acetone to nitroolefins in excellent yields (90-96%) with high enantioselectivities (up to 97% ee).

Biologically important and synthetically challenging spirocyclopentaneoxindoles with four contiguous stereocenters including one spiroquaternary stereocenter have been constructed in good yields (72-87%) with excellent diastereoselectivity (16:1→30:1 dr) and enantioselectivity (93→99% ee) by a combined Ru-catalyzed cross-metathesis/organocatalyzed asymmetric double-Michael addition sequence.

Starting from peptidomimetic BACE-1 inhibitors, the P2 amino acid including the P2/P3 peptide bond was replaced by a rigid 3-aminomethyl cyclohexane carboxylic acid. Co-crystallization revealed an unexpected binding mode with the P3/P4 amide bond placed into the S3 pocket resulting in a new hydrogen bond interaction pattern. Further optimization based on this structure resulted in highly potent BACE-1 inhibitors with selectivity over BACE-2 and cathepsin D.

An unprecedented effect of the ligand-to-metal ratio on the stereofacial selection in the copper-catalyzed enantioselective addition of terminal alkynes to N-PMP-α-imino esters was observed. An excess of ligand was found not to be beneficial, on the contrary, an excess of copper was found to be beneficial. Moreover, both enantiomers of the alkynylation product were obtained with almost the same enantiomeric excess with the same chiral ligand by simply adjusting the ligand-to-metal ratio. The investigation of the mechanism demonstrated the presence of a positive nonlinear effect [(+)-NLE].

The first organocatalytic synthesis of terminal propargylic amines from aldehydes via tandem amination/Seyferth― Gilbert alkynylation has been developed. The described protocol provides the formal addition products of acetylene (HC≡CH) to aliphatic imines, which are not easily obtained directly.

Bifunctional chiral tertiary amine thioureas derived from both α-amino acids and carbohydrates were developed. These organocatalysts promoted the enantioselective conjugate addition of acetylacetone to various aromatic and aliphatic nitroolefins at room temperature in good yields (up to 93 %) and with good enantioselectivity (up to 90 % ee). Furthermore, an interesting matched–mismatched effect of two different chiral units in a chiral organocatalyst was disclosed. Both enantiomers of a product can be achieved in almost the same enantiomeric excess with the “matched” and “mismatched” chiral organocatalysts simply by changing the solvent from THF to toluene. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Lewis acid catalyzed isomerization of 7-oxabicyclic alkenes into 1 -naphthol derivatives in high yields (87-98%) under mild reaction conditions has been developed. The mechanism of this reaction is briefly postulated.

A short review on the development and application of chiral primary amine catalysts in organocatalytic enantioselective reactions has been described.

A highly diastereo- and enantioselective method for the construction of vicinal tetrasubstituted stereocenters through the first catalytic asymmetric Mannich reaction of linear α-substituted MTMs with isatin N-Boc ketimines has been developed. This protocol provides atom-economic synthesis of less accessible 3-aminooxindoles bearing vicinal tetrasubstituted stereocenters. Notably, it also constitutes the first example of stereoselective synthesis of β-amino thioesters bearing vicinal tetrasubstituted stereocenters.

[reaction: see text] The conjugate addition of symmetrical 2-nitroalkanes to 2-cycloalkenones catalyzed by trans-4,5-methano-l-proline proceeds with99% ee and excellent chemical yields. 1-Nitroalkanes afford diastereomeric syn/anti products that can be separated with good individual enantioselectivities. Proline hydroxamic acid and its trans-4,5-methano -l-proline hydroxamic acid are also effective organocatalysts in the addition of 2-nitropropane to 2-cyclohexenone (75% and 81% ee, respectively).

The first diastereoselective synthesis of paeonilide, a novel anti-PAF-active monoterpenoid, starting from R-(-)-carvone was reported. The absolute configuration for paeonilide was also established.

The first method for the asymmetric synthesis of C3-monosubstituted chiral carbazolones, structural motifs common in medicinal chemistry, has been achieved using Pd-catalyzed decarboxylative protonation of carbazolones. This methodology has been applied to the first catalytic enantioselective formal synthesis of (−)-aspidofractinine with step economy and simplicity.

The catalytic enantioselective conjugate addition of acetaldehyde to polyconjugated substrates, nitrodienynes and nitroenynes, has been accomplished using organocatalysis. Various functionalized 1,3-enynes and propargylic compounds were obtained in moderate to good yields with high enantioselectivity. The synthetic utilities of the conjugate addition reactions have been highlighted in the concise total synthesis of (+)-α-lycorane and the metal-free synthesis of chiral β-alkynyl acids.

The catalytic enantioselective and divergent total syntheses of Aspidosperma alkaloids (+)-10-oxocylindrocarpidine 7, (+)-cylindrocarpidine 1, (−)-N-acetylcylindrocarpinol 6, and (+)-aspidospermine 8 have been accomplished in 11 steps from a common precursor (15) on the basis of a highly concise route. The route features three metal-catalyzed reactions, including the key Pd-catalyzed decarboxylative asymmetric allylation of carbazolones developed in our laboratory. Our syntheses, using a combination of C–H activation, enantioselective catalysis, and collective synthesis, represent the first total synthesis of 10-oxocylindrocarpidine and the first asymmetric total synthesis of cylindrocarpidine and N-acetylcylindrocarpinol.

The first catalytic asymmetric [2 + 2] cycloaddition of oxabicyclic alkenes and terminal alkynes has been developed. This iridium-catalyzed enantioselective [2 + 2] cycloaddition allows the formation of four stereocenters in a single step with excellent enantioselectivity (94--99% ee).

The first copper(I)-catalyzed direct three-component coupling of ethyl glyoxylate,p-anisidine, and terminal alkynes has been developed. This protocol provides an efficient method to prepare β,γ-alkynyl α-amino acid derivatives in good yields.

This is the first metal-catalyzed 1,4-selective asymmetric addition of malonates to nitroenynes using a nickel(II)-diamine catalyst.

Recently, the combination of transition metal catalysts and organocatalysts has emerged as a new and powerful strategy for the development of innovative and valuable chemical reactions that are not possible when only one of the two catalysts is employed. The development of this combined catalytic strategy and its applications in different types of reactions are summarized in this chapter.

An intramolecular approach incorporating a Michael addition followed by a palladium-mediated arylation of ketone towards the synthesis of Amaryllidaceae alkaloid (′)-γ-lycorane was reported.

A new class of chiral primary amine catalysts bearing multiple hydrogen-bonding donors have been designed and synthesized. The newly developed bifunctional organocatalysts efficiently catalyzed not only enantioselective conjugate addition of aromatic ketones to nitroolefins in good yields (up to 87%) with excellent enantioselectivities (97→99% ee) but also enantioselective conjugate addition of acetone to nitroolefins in excellent yields (90–96%) with high enantioselectivities (up to 97% ee).

The first catalytic asymmetric conjugate addition of 1,3-dicarbonyl compounds to nitroenynes catalyzed by cinchona alkaloid-based thiourea organocatalysts has been developed. The 1,4-addition adducts were obtained solely, in moderate to good yields (up to 93 %) with good enantioselectivities (up to 99 % ee). This protocol affords a conceptually different entry to the precursors of pharmaceutically important chiral β-alkynyl acid derivatives and synthetically useful chiral nitroalkynes. Notably, the protocol worked well with both aryl- and alkyl-substituted alkynyl substrates.