Reformatsky Reaction to Alkynyl N-tert-Butanesulfinyl Imines: Lewis Acid Controlled Stereodivergent Synthesis of β-Alkynyl-β-Amino Acids

Amide phosphonium salt catalyzed enantioselective Mannich addition of isoxazole-based nucleophiles to β,γ-alkynyl-α-ketimino esters

An enantioselective Mannich addition of 3,5-disubstituted 4-nitroisoxazoles to β,γ-alkynyl-α-ketimino esters promoted by an amide phosphonium salt-based catalyst has been developed. N-Cbz-protected ketimino esters with various aryl substituents attached to the alkyne unit were reacted with a series of isoxazoles with different substitution patterns. Chiral tertiary propargylic amine products were obtained with moderate to good yields and enantioselectivities. TIPS- and cyclopropyl-substituted alkynyl ketimines were also examined in the current system and the desired products were obtained with moderate yields and enantioselectivities. The potential scalability and utility of the current protocol were demonstrated by carrying out a relatively larger scale reaction followed by further transformations.

Organocatalytic Enantioselective Conjugate Alkynylation of β-Aminoenones: Access to Chiral β-Alkynyl-β-Amino Carbonyl Derivatives

Readily available potassium alkynyltrifluoroborates were used for organocatalytic asymmetric conjugate alkynylation of β-enaminones. The interception of a modified binaphthol catalyst and in situ generated organodifluoroboranes proved important to access functionalized β-alkynyl-β-amino carbonyls and derivatives with improved chemo-reactivity and enantio-induction. Mechanistic studies revealed the impact of molecular sieves on efficiency and stereocontrol. The products undergo additional functionalization to yield a diverse set of valuable β-alkynyl-β-amino carbonyl scaffolds.

Enantioselective synthesis of chiral α-alkynylated thiazolidones by tandem S-addition/acetalization of alkynyl imines

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.