Regiocontrolled synthesis of enantioenriched 2-substituted dehydropiperidines by stereospecific allyl-allyl cross-coupling of a chiral allylic boronate.

The palladium-catalyzed cross-coupling of an optically enriched dehydropiperidinyl boronate with cinnamyl carbonates was optimized to minimize stereochemical erosion. Although the coupling of two unsymmetrical allyl fragments may generate four possible regioisomers, the optimal procedure using ( p -CF 3 C 6 H 4 ) 3 P as the ligand affords linear 2-allylated 3,4-dehydropiperidines exclusively (>98 : 2 rr) with enantiospecificity up to 99%.