Diastereoselective Synthesis of Less Accessible Fluorine-Containing Acyclic Tetrasubstituted Stereocenters via Electrophilic Fluorination of ß,ß-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 ß,ß-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 Electrophilic α-Alkynylation of α,α-Disubstituted N-tert-Butanesulfinyl Ketimines for Construction of Less Accessible Acyclic Quaternary Stereocenters.

In order to construct less accessible acyclic quaternary stereocenters, a protocol was developed to α-alkynylate α,α-disubstituted N-tert-butanesulfinyl ketimines stereoselectively using 1-(2-trimethylsilylethynyl)-1,2-benziodoxol-3(1H)-one in the presence of fluoride. Despite the steric and electrical similarity between the two α-substituents, the entire reaction proceeded in a strongly stereoselective manner: tBuOK promoted α-deprotonation of the acyclic ketimine to generate stereodefined fully substituted aza-enolates, which stereoselectively formed C-C bonds with electrophilic alkynylation reagents, affording α-alkynylation products with excellent stereocontrol.

Chiral spiro phosphoric acid-catalysed enantioselective reaction of ketenes with N-H pyrroles.

In the presence of a chiral spiro phosphoric acid catalyst, the asymmetric reaction of disubstituted ketenes with N-H pyrroles occurred to afford enantioenriched C-acylated pyrroles bearing α-stereogenic carbon centres. The described reaction constitutes a rare example of a catalytic asymmetric reaction of ketenes with carbon-based nucleophiles.