Development of Catalytic Enantioselective Mannich Reactions Using Esters

Catalytic enantioselective Mannich reactions of simple nonactivated esters proceeded using a chiral potassium strong base catalyst prepared from a chiral bisoxazoline and potassium hexamethyldisilazide. Alkyl acetates, alkyl propionates, and an alkyl butyrate were employed as the simple esters, and the desired reactions proceeded smoothly to afford Mannich products in good to high yields with high enantioselectivities. One of the products was successfully employed in the asymmetric total synthesis of Maraviroc.

Boron-Catalyzed α-Functionalizations of Carboxylic Acids

Catalytic, chemoselective, and asymmetric α-functionalizations of carboxylic acids promise up-grading simple feedstock materials to value-added functional molecules, as well as late-stage structural diversifications of multifunctional molecules, such as drugs and their leads. In this personal account, we describe boron-catalyzed α-functionalizations of carboxylic acids developed in our group (five reaction types). The reversible boron carboxylate formation is key to the acidification of the α-protons and enolization using mild organic bases, allowing for chemoselective and asymmetric bond formations of carboxylic acids. The ligand effects on reactivity and stereoselectivity, substrate scopes, and mechanistic insights are summarized.

KOtBu-catalysed α-homoallylic alkylation of acyclic amides with 1-aryl-1,3-dienes

Herein, we report a KOtBu-catalysed α-homoallylic alkylation of acyclic amides with 1-aryl-1,3-dienes. With this transition metal-free and atom-economic protocol, a series of α-homoallylic alkylated acyclic amides were synthesized in good to excellent yields. This transformation is proposed to proceed through a cation-π interaction-based C-C bond formation from the in situ-generated potassium enolate with the diene unit.

Development of chiral potassium strong Brønsted base catalysts for enantioselective carbon-carbon bond-forming reactions

Chiral alkaline metal Brønsted bases are traditional and reliable promoters in enantioselective catalysis. Here, new chiral potassium strong base catalysts were developed for enantioselective carbon-carbon bond-forming reactions of weakly acidic carbon pronucleophiles. Chiral potassium amide or alkyl potassium catalyzed enantioselective addition reactions to imines or α,β-unsaturated amides with good to high enantioselectivities. The good potential of chiral potassium Brønsted bases to act as proton transfer catalysts has been shown.

Chiral Metal Salts as Ligands for Catalytic Asymmetric Mannich Reactions with Simple Amides

Catalytic asymmetric Mannich reactions of imines with weakly acidic simple amides were developed using a chiral potassium hexamethyldisilazide (KHMDS)-bis(oxazoline) potassium salt (K-Box) catalyst system. The desired reactions proceeded to afford the target compounds in high yields with high diastereo- and enantioselectivities. It was suggested that a K enolate interacted with K-Box to form a chiral K enolate that reacted with imines efficiently. In this system, K-Box (potassium salt of Box) worked as a chiral ligand of the active potassium species.

Alkali-amide-catalyzed divergent sp2 and sp3 C–H bonds alkylation of alkylthiophenes with alkenes

Divergent sp² and sp³ C–H bonds alkylation of alkylthiophenes was achieved selectively with LDA and KHMDS catalysts, providing not only atom-economical synthesis approaches but also some insights in the different behaviours of the alkali amides.

Synthesis of diarylalkanes through an intramolecular/intermolecular addition sequence by auto-tandem catalysis with strong Brønsted base

An auto-tandem catalysis with a strong Brønsted base enabled the synthesis of diarylalkanes containing a benzofuran moiety. Potassium tert-butoxide efficiently catalyzed both the intramolecular cyclization of less acidic ortho-alkynylaryl benzyl ethers and the following intermolecular addition of diarylmethanes to styrenes, demonstrating the high potential of the catalysis in organic synthesis.

New Dimensions of Brønsted Base Catalyzed Carbon–Carbon Bond-Forming Reactions

Catalytic carbon–carbon bond-forming reactions of weakly acidic carbon pronucleophiles (pK a in DMSO ≥30) were developed using strong alkaline metal Brønsted bases as catalysts. Not only weakly acidic amides, esters, nitriles, sulfonamides without any activating group, and alkyl azaarenes, but also alkyl arenes such as toluene, were applicable for the reactions, which are difficult to be applied in typical Brønsted base catalyzed reactions. Expansion to enantioselective reactions was also revealed to be possible. The reactions are atom economical and require only inexpensive alkaline metals rather than precious transition metals.

1 Introduction

2 Catalytic Direct-Type Addition Reactions of Weakly Acidic Carbonyl and Related Pronucleophiles

3 Catalytic Direct-Type Addition Reactions of Alkyl Azaarenes

4 Catalytic Direct-Type Addition Reactions of Alkyl Arenes

5 Conclusion

Base-promoted addition of DMA with 1,1-diarylethylenes: application to a total synthesis of (-)-sacidumlignan B

A base-promoted addition of DMA (N,N-dimethylacetamide) to 1,1-diarylethylenes has been developed, and it provides a new strategy for the synthesis of N,N-dimethyl-4,4-diarylbutanamides from 1,1-diarylethylenes at room temperature. This method allows us to achieve the goal of synthesizing (-)-sacidumlignan B, and provides simple operation and broad substrate scope by avoiding the use of transition metal catalysts.

Alkyl lithium-catalyzed benzylic C–H bond addition of alkyl pyridines to α-alkenes

The alkyl lithium catalyst successfully achieved the benzylic C–H bond addition of alkyl pyridines to α-alkenes, and displayed distinct selectivity from those of transition metal catalysts.

Combined KH/alkaline-earth metal amide catalysts for hydrogenation of alkenes

Breaking saline KH: The combined KH/alkaline-earth metal amide catalysts display much better catalytic activity than their components in the hydrogenation of alkenes, suggesting the degradation and activation of saline KH with the metal amides.

Lithium Diisopropylamide Catalyzed Allylic C-H Bond Alkylation with Styrenes

Allylic substitution reactions, a well-established approach for new bond construction, often need transition-metal catalysts and stoichiometric amounts of organometallic reagents, strong bases, or oxidants. Lithium diisopropylamide (LDA), a widely used and commercially available Brønsted base, is herein reported to catalyze the allylic C-H bond addition of 1,3-diarylpropenes to styrenes. Preliminary mechanism studies have provided a solid structure of the π-allyllithium intermediate and revealed the unique catalytic roles of LDA and its conjugate acid diisopropylamine.

Potassium-Zincate-Catalyzed Benzylic C-H Bond Addition of Diarylmethanes to Styrenes

Direct functionalization of the benzylic C-H bond of diarylmethanes is an important strategy for the synthesis of diarylmethine-containing compounds. However, the methods developed to date for this purpose require a stoichiometric amount (usually more) of either a strong base or an oxidant. Reported here is the first catalytic benzylic C-H bond addition of diarylmethanes to styrenes and conjugated dienes. A potassium zincate complex, generated from potassium benzyl and zinc amide, acts as a catalyst and displays good activity and chemoselectivity. Considering the atom economy of the reaction and the ready availability of the catalyst, this reaction constitutes a practical, efficient method for diarylalkane synthesis.

Catalytic alkylation reactions of weakly acidic carbonyl and related compounds using alkenes as electrophiles

Catalytic alkylation reactions of weakly acidic carbonyl and related pronucleophiles such as amides, esters, and sulfonamides with substituted alkenes have been reported.

Catalytic Carbon-Carbon Bond-Forming Reactions of Weakly Acidic Carbon Pronucleophiles Using Strong Brønsted Bases as Catalysts

Catalytic carbon-carbon bond-forming reactions of weakly acidic carbon pronucleophiles with N-aryl imines, α,β-unsaturated amides, and others under proton-transfer conditions were developed by designing strongly basic reaction intermediates known as product bases. The reactions proceed smoothly in the presence of a catalytic amount of strong base such as KH or alkaline metal amides. Modification of the metal cations by using chiral macrocyclic crown ethers allowed catalytic asymmetric 1,4-addition reactions to proceed with high enantioselectivities. This concept can be applied to Brønsted-base-catalyzed reactions of a wide range of weakly acidic carbon pronucleophiles.

Intramolecular addition of benzyl anion to alkyne utilizing [1,2]-phospha-Brook rearrangement under Brønsted base catalysis

A novel reaction system for intramolecular addition of benzyl anions to alkynes was developed by utilizing the [1,2]-phospha-Brook rearrangement under Brønsted base catalysis. The present reaction is a rare example of a catalytic addition reaction of an unstabilized benzyl anion under Brønsted base catalysis.

Development of chiral metal amides as highly reactive catalysts for asymmetric [3 + 2] cycloadditions

Highly efficient catalytic asymmetric [3 + 2] cycloadditions using a chiral copper amide are reported. Compared with the chiral CuOTf/Et₃N system, the CuHMDS system showed higher reactivity, and the desired reactions proceeded in high yields and high selectivities with catalyst loadings as low as 0.01 mol %.

Catalytic asymmetric direct-type 1,4-addition reactions of simple esters

Catalytic asymmetric 1,4-addition reactions of simple esters have been developed. The desired reactions proceeded smoothly with high enantioselectivities.

Brønsted base-catalyzed three-component coupling reaction of α-ketoesters, imines, and diethyl phosphite utilizing [1,2]-phospha-Brook rearrangement

A three-component coupling reaction of α-ketoesters, imines, and diethyl phosphite under Brønsted base catalysis was developed by utilizing the [1,2]-phospha-Brook rearrangement.

A cooperative water effect in proazaphosphatrane-catalysed heterocycle synthesis

Water activated isocyanide is deprotonated by the organosuperbase proazaphosphatrane; no deprotonation of water could be observed.