Mukaiyama Mannich Research Articles

B(C6F5)3-Catalyzed Diastereoselective and Divergent Reactions of Vinyldiazo Esters with Nitrones: Synthesis of Highly Functionalized Diazo Compounds.

Herein we report a mild, transition-metal-free, highly diastereoselective Lewis acid catalyzed methodology toward the synthesis of isoxazolidine-based diazo compounds from the reaction between vinyldiazo esters and nitrones. Interestingly, the isoxazolidine products were identified to have contrasting diastereoselectivity to previously reported metal-catalyzed reactions. Furthermore, the same catalyst can be used with enol diazo esters, prompting the formation of Mukaiyama-Mannich products. These diazo products can then be further functionalized to afford benzo[b]azepine and pyrrolidinone derivatives.

Short Synthesis of Alkaloid (-)-205B.

The alkaloid (-)-205B has in the past served as a testing ground for novel approaches in nitrogen heterocycle synthesis. We herein report a highly straightforward synthesis of (-)-205B in just six synthetic steps, making it the shortest route currently known. The central steps of our approach are a vinylogous Mukaiyama-Mannich reaction to establish the first two stereogenic centers with excellent diastereo- and enantiocontrol followed by zinc-mediated Barbier allylation to set the third chiral center with high substrate control. Upon cyclization of the Barbier product to lactam and enolate methylation, the third ring is annulated by a one-pot sequence of lactam reduction and aza-Prins cyclization to directly set the final stereogenic center with complete cis-stereoselectivity. As the iminium ion undergoing the aza-Prins cyclization rapidly isomerized to a planar enamine intermediate, the alkaloid was eventually obtained as a 1:1 mixture of C6 diastereomers, which were readily separated by chromatography. Yet, the target natural product was obtained isomerically pure in an overall yield of 12%, which compares favorably with all previous syntheses.

Organocatalytic Enantioselective Mukaiyama–Mannich Reaction of Isatin‐Derived Ketimines for the Synthesis of Oxindolyl‐β3, 3‐Amino Acid Esters

Mukaiyama-Mannich reactions of ester enolate equivalents with aldimines have been elegantly used for the asymmetric synthesis of β-amino acids; nevertheless, the corresponding asymmetric reaction employing ketimines are unexplored. Herein, the first organocatalytic enantioselective Mukaiyama-Mannich reaction employing isatin-derived ketimines with unsubstituted silyl ketene acetals is disclosed towards the scalable synthesis of 2-oxoindolinyl-β3, 3 -amino acid esters at room temperature with excellent enantioselectivities (ee >99.5 %). Ultra-low catalyst loadings (as low as 250 ppm) could be used for the quantitative product formation with high enantiopurity. The synthetic utility of this protocol has been showcased in the short formal synthesis of pharmaceutically demanded (+)-AG-041R, a potent gastrin/CCK-B receptor antagonist.

Asymmetric Vinylogous Mukaiyama‐Mannich Reactions of Heterocyclic Siloxy Dienes with Ellman's Fluorinated Aldimines

AbstractVinylogous Mukaiyama Mannich reactions of furan and pyrrole based dienoxy silanes with α‐fluoroalkyl sulfinyl imines provide a powerful synthetic access to a variety of amino fluoroalkyl γ‐butenolide‐type and butyrolactam frameworks with high regio‐ and diastereoselectivity. Anti‐configured adducts were obtained in all cases, independent of the nature of the heteroatom (O or N) present in the dienoxy silane. The absolute configuration of the adducts prepared was unequivocally established by X‐ray crystallographic analysis. It is noteworthy that the introduction of substituents at the γ‐position of the heterocyclic partner allows the generation of adducts bearing chiral quaternary centers.magnified image

Organocatalytic Mukaiyama Mannich Reactions of 2,5-Bis(trimethylsilyloxy)furan.

The organocatalytic synthesis of densely substituted mono- and bis-γ-lactams involving the Mukaiyama Mannich addition of 2,5-bis(trimethylsilyloxy)furan to imines is described. Use of a ditoluenesulfonylimide catalyst produces γ-lactams from monoaddition, whereas a more acidic catalyst (triflic acid) produces fused bis-lactams from double addition. Optimized organocatalytic conditions allow for the selective synthesis of either desired core as well as the one-pot, multicomponent assembly of the trisubstituted monolactams from aldehydes, amines, and bis-trimethylsilyloxyfuran. An examination of chiral acids found these organocatalysts to be highly active and diastereoselective in the monoaddition reaction, albeit with no enantioselectivity.

Chiral Zinc(II)‐Catalyzed Enantioselective Tandem α‐Alkenyl Addition/Proton Shift Reaction of Silyl Enol Ethers with Ketimines

AbstractA new catalytic asymmetric tandem α‐alkenyl addition/proton shift reaction of silyl enol ethers with ketimines was serendipitously discovered in the presence of chiral N,N′‐dioxide/ZnII complexes. The proton shift preferentially proceeded instead of a silyl shift after α‐alkenyl addition of silyl enol ether to the ketimine. A wide range of β‐amino silyl enol ethers were synthesized in high yields with good to excellent ee values. Control experiments suggest that the Mukaiyama–Mannich reaction and tandem α‐alkenyl addition/proton shift reaction are competitive reactions in the current catalytic system. The obtained β‐amino silyl enol ethers were easily transformed into β‐fluoroamines containing two vicinal tetrasubstituted carbon centers.

A Sc(OTf)3 catalyzed Mukaiyama–Mannich reaction of difluoroenoxysilanes with unactivated ketimines

The first example of a Mukaiyama–Mannich reaction of difluoroenoxysilanes with unactivated ketimines catalyzed by Sc(OTf)3 is described.

Catalytic Asymmetric Mukaiyama-Mannich Reaction of Cyclic C-Acylimines with Difluoroenoxysilanes: Access to Difluoroalkylated Indolin-3-ones.

A catalytic enantioselective Mukaiyama-Mannich reaction of cyclic C-acylimines with difluoroenoxysilanes is reported. (S)-TRIP enables the enantioselective synthesis of a series of novel difluoroalkylated indolin-3-ones bearing a quaternary stereocenter in up to 97% yield and 98% ee. The synthetic utility of this protocol is highlighted by efficient conversion of the products to the corresponding indolin-3-one derivatives without any erosion of the enantiopurity.

A Highly Efficient Gold(I)-Catalyzed Mukaiyama–Mannich Reaction of α-Amino Sulfones with Fluorinated Silyl Enol Ethers To Give β-Amino α-Fluorinated Ketones

Ph3PAuOTf was identified as a powerful catalyst for the ­Mukaiyama–Mannich reaction of fluorinated silyl enol ethers with α-amino sulfones. This provides ready access to β-amino α-fluorinated ketones in good to excellent yields.

In situ generation of N-Boc-protected alkenyl imines: controlling the E/Z geometry of alkenyl moieties in the Mukaiyama–Mannich reaction

Readily available Boc-protected Z-alkenyl aminals could be used as Z-alkenyl and E-alkenyl imine precursors under acidic conditions. In the Mukaiyama-Mannich reaction of Z-alkenyl Boc-aminals, the E/Z geometry of the products was controlled by the catalyst used. The present method was also applied to asymmetric Mukaiyama-Mannich reactions.

Ni(ii)-Catalyzed enantioselective Mukaiyama–Mannich reaction between silyl enol ethers and cyclic N-sulfonyl α-ketiminoesters

The first Ni(ii)-catalyzed Mukaiyama–Mannich reaction of cyclic N-sulfonyl α-ketiminoesters with silyl enol ethers was realized and provided enantioenriched benzofused sultams containing a quaternary α-amino ester.

Dimeric BINOL-Derived Disulfonimide Mukaiyama–Mannich Catalyst

Key words Mukaiyama–Mannich reaction - disulfonimides - amino esters - imines - ketene silyl acetals

ChemInform Abstract: A Powerful Chiral Phosphoric Acid Catalyst for Enantioselective Mukaiyama—Mannich Reactions.

AbstractAromatic and aliphatic imines, including challenging N‐(hydroxyphenyl)‐substituted derivatives, are transformed with complex ketene silyl acetals bearing two different substituents on the vinyl carbon in the presence of chiral BINOL‐derived phosphoric acid or amide catalysts.

A Disulfonimide Catalyst for Highly Enantioselective Mukaiyama–Mannich Reaction

A new BINOL-derived chiral disulfonimide has been developed by introducing 4-methyl-3,5-dinitrophenyl substituents at its 3- and 3'-positions. This chiral disulfonimide catalyst displays high catalytic efficacy toward the asymmetric Mukaiyama-Mannich reaction of imines with ketene silyl acetals leading to β-amino acid esters in good yields (up to 99%) with high diastereoselectivities (syn/anti up to 97:3) and enantioselectivities (up to 98% ee). The long-standing problem of the chiral phosphoric acid-catalyzed asymmetric Mukaiyama-Mannich reaction that requires a 2-hydroxyphenyl moiety was solved by this disulfonimide catalyst.

ChemInform Abstract: An Aromatic Ion Platform for Enantioselective Broensted Acid Catalysis.

AbstractA novel chiral Broensted acid is prepared in one step from (‐)‐menthol and readily available pentacarbomethoxycyclopentadiene and utilized in both Mukaiyama—Mannich and oxocarbenium aldol reactions with high efficiency and enantioselectivity.

A Powerful Chiral Phosphoric Acid Catalyst for Enantioselective Mukaiyama–Mannich Reactions

AbstractA new BINOL‐derived chiral phosphoric acid bearing 2,4,6‐trimethyl‐3,5‐dinitrophenyl substituents at the 3,3′‐positions was developed. The utility of this chiral phosphoric acid is demonstrated by a highly enantioselective (ee up to >99 %) and diastereoselective (syn/anti up to >99:1) asymmetric Mukaiyama–Mannich reaction of imines with a wide range of ketene silyl acetals. Moreover, this method was successfully applied to the construction of vicinal tertiary and quaternary stereogenic centers with excellent diastereo‐ and enantioselectivity. Significantly, BINOL‐derived N‐triflyl phosphoramide constitutes a complementary catalyst system that allows the title reaction to be applied to more challenging imines without an N‐(2‐hydroxyphenyl) moiety.

A Powerful Chiral Phosphoric Acid Catalyst for Enantioselective Mukaiyama-Mannich Reactions.

A new BINOL-derived chiral phosphoric acid bearing 2,4,6-trimethyl-3,5-dinitrophenyl substituents at the 3,3'-positions was developed. The utility of this chiral phosphoric acid is demonstrated by a highly enantioselective (ee up to >99 %) and diastereoselective (syn/anti up to >99:1) asymmetric Mukaiyama-Mannich reaction of imines with a wide range of ketene silyl acetals. Moreover, this method was successfully applied to the construction of vicinal tertiary and quaternary stereogenic centers with excellent diastereo- and enantioselectivity. Significantly, BINOL-derived N-triflyl phosphoramide constitutes a complementary catalyst system that allows the title reaction to be applied to more challenging imines without an N-(2-hydroxyphenyl) moiety.

ChemInform Abstract: Organocatalytic Enantioselective Mukaiyama—Mannich Reaction of Fluorinated Enol Silyl Ethers and Cyclic N‐Sulfonyl Ketimines.

AbstractIn the presence of a quinine‐based bifunctional urea catalyst, cyclic N‐sulfonyl ketimines react with fluorinated enol silyl ethers to afford benzosultam based α‐amino acid derivatives possessing a fluoroalkyl group in high to excellent yields and stereoselectivities.

ChemInform Abstract: One‐Pot Silyl Ketene Acetal‐Formation Mukaiyama—Mannich Additions to Imines Mediated by Trimethylsilyl Trifluoromethanesulfonate.

AbstractThioesters, esters, N‐arylamides and ketones react successfully with N‐arylimines if a Tms‐O‐Tf/trialkylamine mixture is used.

ChemInform Abstract: A Highly Efficient Mukaiyama—Mannich Reaction of N‐Boc Isatin Ketimines and Other Active Cyclic Ketimines Using Difluoroenol Silyl Ethers Catalyzed by Ph3PAuOTf.

AbstractCyclic ketimines (I), and active cyclic sulfonimines (VIII) undergo Mukaiyama—Mannich reactions with difluoroenol silyl ethers (II) catalyzed by title Au(I) complex affording cyclic compounds substituted by an α,α‐difluoroketone moiety.