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

Stereoselective Vinylogous Aza-Pummerer Reaction of β,β-Disubstituted Enesulfinamides

Treatment of multisubstituted NH-enesulfinamides with tosyl isocyanate (TsNCO) at room temperature results in the formation of α-tosylcarbamoyloxy N-sulfenyl ketimines with high enantioselectivity. This process is believed to proceed via a vinylogous aza-Pummerer-type reaction pathway in which the sulfinyl oxygen atom in the enesulfinamides undergoes nucleophilic attack on tosyl isocyanate, triggering the subsequent transformations that enable the transfer of chirality from sulfur to carbon.

Stereoselective Enesulfinamide-Sulfinylimine Tautomerization of β,β-Disubstituted Enesulfinamides

In the presence of cesium fluoride and organosilicon reagent, β,β-disubstituted NH-enesulfinamides undergo stereoselective enesulfinamide-sulfinylimine tautomerization at room temperature, resulting in the formation of α-branched N-sulfinyl ketimines in good yields with high stereoselectivity. A variety of acyclic ketone surrogates α-substituted with two electronically and sterically similar groups (e.g., methyl and ethyl), which are typically challenging to access through conventional protocols involving stereoselective protonation of enolates and their equivalents, have been effectively synthesized.

Stereoselective Aminomethylation of β,β-Disubstituted Enesulfinamides: Asymmetric Construction of Less Accessible Acyclic α,α-Disubstituted α-Aminomethylated Ketimines

β,β-Disubstituted enesulfinamides undergo stereoselective nucleophilic addition to the formaldehyde imines, in situ formed from tosylmethylcarbamates, affording α-aminomethylated ketimines bearing a challenging acyclic quaternary stereocenter substituted by two sterically and electronically similar groups (e.g., Me and Et). The defined geometry of the C═C bond in the enesulfinamides, combined with the strong chiral induction offered by their chiral sulfinyl group, ensures precise stereocontrol during the formation of the new C-C bond.

Stereoselective Construction of Less-Accessible Acyclic Quaternary Carbon Stereocenters via Rhodium-Catalyzed Allylic Alkylation of β,β-Disubstituted Enesulfinamides

In the presence of Wilkinson's catalyst, the N-sulfinyl metalloenamines derived from NH-deprotonation of β,β-disubstituted enesulfinamides undergo nucleophilic allylic substitution with allyl carbonate, affording α-allylated ketimines with high stereoselectivity. These allylation products possess challenging acyclic quaternary stereocenters containing one allyl group and two alkyl groups that are both sterically and electronically similar (e.g., Me and Et). By utilizing appropriate stereoisomers of enesulfinamides, it becomes feasible to selectively access each of the four potential stereoisomers of the allylation products, thereby facilitating the selective synthesis of stereoisomers of α-tertiary chiral amines featuring a β-quaternary stereocenter through imino nucleophilic addition.

Asymmetric Construction of Ethenyl-Substituted Acyclic Quaternary Stereocenters at the α-Position of Carbonyl Surrogates via Stereoselective Sulfonylvinylation-Reductive Desulfonylation

N-Sulfinyl metalloenamines, derived from geometry-defined β,β-disubstituted enesulfinamides, undergo conjugate addition-elimination reaction with β-tosyl nitroolefin to afford α-sulfonylvinylated ketimines with high stereocontrol. Further desulfonylation using sodium naphthalenide gives carbonyl surrogates bearing a less-accessible acyclic quaternary α-stereocenters substituted with an ethenyl group and two sterically and electronically similar groups (e.g., methyl and ethyl). Synthetic application of the described protocol was demonstrated by enantioselective synthesis of (S)-bakuchiol.

Stereoselective Electrophilic Sulfenylation of β,β-Disubstituted Enesulfinamides: Asymmetric Construction of Less Accessible Acyclic α,α-Disubstituted α-Sulfenylated Ketimines

Current methods for the asymmetric α-sulfenylation of carbonyls cannot be applied to acyclic carbonyls that have two similar substituents at the α-position. This research demonstrated that the electrophilic sulfenylation of geometry-defined acyclic β,β-disubstituted enesulfinamides using S-aryl or S-alkyl benzenethiosulfonates can be highly stereoselective. This process results in enantioenriched α,α-disubstituted α-sulfenylated ketone surrogates with sulfur-containing acyclic tetrasubstituted carbon stereocenters bearing two electronically and sterically similar substituents (e.g., methyl and ethyl). Furthermore, by employing the corresponding stereoisomers of enensulfinamides, any of the four stereoisomers of α-sulfenylated ketimines can be selectively accessed.

Stereoselective Construction of Less-Accessible Acyclic α,α-Disubstituted β-Ketiminonitriles via Electrophilic Cyanation of β,β-Disubstituted Enesulfinamides

The metalloenamines, formed by NH-deprotonation of β,β-disubstituted enesulfinamides, can undergo reactions with commercially available electrophilic cyanating reagents such as tosyl cyanide (TsCN) or 3-oxo-1,2-benziodoxole-1(3H)-carbonitrile (CBX). Through the utilization of appropriate stereoisomers of enesulfinamides, this method enables the selective synthesis of any of the four stereoisomers of α,α-disubstituted β-sulfinylimino nitriles, which feature acyclic quaternary stereocenters and are typically more challenging to synthesize. These compounds can then undergo stereoselective nucleophilic addition, leading to the creation of valuable enantioenriched multisubstituted β-amino carbonyl surrogates with a high degree of structural diversity.

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 Cyclopropanation of Multisubstituted Enesulfinamides: Asymmetric Construction of α-Tertiary Cyclopropylamine Derivatives Containing β-Quaternary Stereocenters

Enesulfinamides with α,β,β-trisubstitution undergo a Simmons-Smith reaction to yield multisubstituted cyclopropylamine derivatives with high stereocontrol. The resulting α-tertiary cyclopropylamine derivatives, which feature β-quaternary stereocenters bearing two electronically and sterically similar substituents (e.g., methyl and ethyl), are seldom achieved by using conventional methods. By adjusting the stereochemistry of the carbon-carbon double bond and/or sulfinyl group within the enesulfinamides, it is feasible to selectively produce four stereoisomers of the cyclopropylamines, each with different absolute configurations at the α- and β-carbons.

Stereoselective Electrophilic Chlorination of β,β-Disubstituted Enesulfinamides with Chloramine-T: Asymmetric Synthesis of Acyclic α,α-Disubstituted α-Chlorinated Carbonyl Surrogates

Enamine and iminium ion-mediated asymmetric organocatalysis was not successful in achieving highly stereoselective α-chlorination of acyclic α,α-disubstituted carbonyls. To address this limitation, an alternative method was developed, which involved the use of geometry-defined persubstituted enesulfinamides to intercept the electrophilic chlorinating reagent. This approach enables the asymmetric construction of challenging acyclic α,α-disubstituted α-chlorinated ketimines with a high degree of stereoselectivity. The use of chloramine-T, a cost-effective and stable chlorine source rarely utilized in asymmetric electrophilic chlorination, plays a crucial role in achieving superior stereocontrol.