Stereoselective Cyclopropanation of Multisubstituted Enesulfinamides: Asymmetric Construction of α-Tertiary Cyclopropylamine Derivatives Containing ß-Quaternary Stereocenters.

Enesulfinamides with α,ß,ß-trisubstitution undergo a Simmons-Smith reaction to yield multisubstituted cyclopropylamine derivatives with high stereocontrol. The resulting α-tertiary cyclopropylamine derivatives, which feature ß-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 ß-carbons.

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

In the presence of boron trifluoride, conjugate addition of organocuprates to α-substituted α,ß-unsaturated N-tert-butanesulfinyl ketimines provides facile access to acyclic ß,ß-disubstituted enesulfinamides with high ratios of geometric isomers. Diverse and challenging to synthesize, multisubstituted aza-enolates bearing two electronically and sterically similar ß-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.

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,ß-unsaturated phosphonates generates C-C bonds with exceptional stereocontrol, and finally paraformaldehyde trapping of the conjugate addition intermediate generates functionalized α-allylated imines.

Construction of Acyclic Quaternary Stereocenters via Mannich-Type Addition of α,α-Disubstituted N-tert-Butanesulfinyl Ketimines to Isatin-Derived Ketimines.

A Mannich reaction of deprotonated, highly enantioenriched α,α-disubstituted N-tert-butanesulfinyl ketimines with isatin-derived ketimines was developed to prepare 3-amino-3-substituted oxindoles bearing an acyclic quaternary stereogenic carbon substituted with two sterically similar groups. The excellent stereocontrol of the deprotonation enabled the formation of metalloenamine intermediates with stereodefined geometry, while the precise facial selectivity of the C-C bond formation allowed the construction of contiguous quaternary and tetrasubstituted stereocenters with excellent stereoselectivity.