Stereocontrolled Construction of Acyclic Quaternary Carbon Centers via α-Hydroxymethylation of α-Branched N-tert-Butanesulfinyl Ketimines

N-Polyfluoroarylation-Triggered Rearrangement of Enesulfinamidines: Asymmetric Synthesis of α-Amino Ketimine Derivatives

Metalloenamines, generated through the α-deprotonation of N-iminosulfinyl ketimines, can be selectively intercepted at their nitrogen atom by highly fluorinated (hetero)arenes. The interaction leads to the formation of N-polyfluoroarylated enesulfinamidine intermediates, which are capable of undergoing [2,3]-sigmatropic rearrangement to yield α-amino ketimine derivatives. The high enantiopurity of the resulting products is ensured by the precise transfer of chirality from the sulfur atom of the iminosulfinyl group to the α-carbon of the ketimine moiety.

Diastereoselective Synthesis of Less Accessible Fluorine-Containing Acyclic Tetrasubstituted Stereocenters via Electrophilic Fluorination of β,β-Disubstituted Metalloenamines

A stereocontrolled protocol was developed to construct less accessible fluorine-containing acyclic tetrasubstituted stereocenters bearing two sterically and electronically similar alkyl groups at the α-position of carbonyls. In this process, tBuOK-promoted stereospecific α-deprotonation of α,α-disubstituted N-tert-butanesulfinyl ketimines or NH deprotonation of β,β-disubstituted enesulfinamides generates geometry-defined multisubstituted metalloenamines, followed by stereoselective electrophilic fluorination with the N-fluoro ammonium salt of quinine, affording the acyclic α-fluorinated ketimines with excellent diastereoselectivities.

Stereoselective Construction of Acyclic β,β-Disubstituted Enesulfinamides via Conjugate Addition of Organocuprates to α-Substituted α,β-Unsaturated N-Sulfinyl Ketimines

In the presence of boron trifluoride, conjugate addition of organocuprates to α-substituted α,β-unsaturated N-tert-butanesulfinyl ketimines provides facile access to acyclic β,β-disubstituted enesulfinamides with high ratios of geometric isomers. Diverse and challenging to synthesize, multisubstituted aza-enolates bearing two electronically and sterically similar β-substituents, which are important precursors for asymmetric construction of the less accessible acyclic quaternary or tetrasubstituted stereocenters at the α-position of ketimines, can be efficiently prepared in good yields with high stereocontrol.

Stereoselective Synthesis of Less Accessible α-Tertiary Amino Ketimines via Electrophilic Amination of α-Branched N-tert-Butanesulfinyl Ketimines

A stereocontrolled electrophilic amination of α-branched N-tert-butanesulfinyl ketimines was developed to construct α-aminoketone derivatives containing less accessible α-tetrasubstituted stereocenters. Stereospecific α-deprotonation of ketimines with potassium tert-butoxide gave stereodefined metalloenamine intermediates that could act as nucleophiles to attack azodicarboxylic derivatives, affording α-aminated products in high yields with excellent stereoselectivities.

Stereocontrolled α-Allylation of α-Branched N-tert-Butanesulfinyl Ketimines via a Michael-Wittig Cascade for the Construction of Acyclic Quaternary Stereocenters

A single-flask cascade of Michael addition and Wittig olefination was developed to allow the stereoselective α-allylic alkylation of α-branched N-tert-butanesulfinyl ketimines for the construction of acyclic quaternary stereocenters bearing two sterically and electronically similar substituents. In this process, tBuOK-promoted stereoselective α-deprotonation gives fully substituted aza-enolates with a stereodefined geometry, Michael addition with α,β-unsaturated phosphonates generates C-C bonds with exceptional stereocontrol, and finally paraformaldehyde trapping of the conjugate addition intermediate generates functionalized α-allylated imines.