Enantioselective Alkynylation of Unstabilized Cyclic Iminium Ions.

An enantioselective copper-catalyzed alkynylation of unstabilized cyclic iminium ions has been developed. Whereas such alkynylations typically utilize pyridinium, quinolinium and isoquinolinium intermediates, this method enables use of cyclic iminium ions unstabilized by resonance. With the use of a Lewis acid and copper catalyst, these iminium ions are generated from readily available hemiaminal methyl ethers and transformed into highly enantioenriched α-alkynylated cyclic amines.

Vinylation of Benzylic Amines via C-N Bond Functionalization of Benzylic Pyridinium Salts.

Cross-couplings of benzylic pyridinium salts and vinylboronic acids or esters have been developed. Via these benzylic pyridinium intermediates, benzylic amines can be engaged in these cross-couplings via C-N bond functionalization. This method boasts mild reaction conditions and excellent tolerance for heteroaryl substituents and a range of functional groups.

Transforming Benzylic Amines into Diarylmethanes: Cross-Couplings of Benzylic Pyridinium Salts via C-N Bond Activation.

A nickel-catalyzed cross-coupling of benzylic pyridinium salts with arylboronic acids was developed. Coupled with chemoselective pyridinium formation, this method allows benzyl primary amines to be efficiently converted to di(hetero)arylmethanes. Excellent heteroaryl and functional group tolerance is observed, and a one-pot procedure enables benzylic amines to be converted to diarylmethanes directly.

Stereoselective formation of trisubstituted vinyl boronate esters by the acid-mediated elimination of α-hydroxyboronate esters.

The copper-catalyzed diboration of ketones followed by an acid-catalyzed elimination leads to the formation of 1,1-disubstituted and trisubstituted vinyl boronate esters with moderate to good yields and selectivity. Addition of tosic acid to the crude diboration products provides the corresponding vinyl boronate esters upon elimination. The trisubstituted vinyl boronate esters are formed as the (Z)-olefin isomer, which was established by subjecting the products to a Suzuki-Miyaura coupling reaction to obtain alkenes of known geometry.