Complex Boron-Containing Molecules through a 1,2-Metalate Rearrangement/anti-SN2′ Elimination/Cycloaddition Reaction Sequence

The three-component coupling of benzylamines, boronic esters, and 4-phenyl-3 H -1,2,4-triazole-3,5(4 H )-dione (PTAD) is reported. The boronate complex formed from an ortho -lithiated benzylamine and a boronic ester undergoes a stereospecific 1,2-metalate rearrangement/ anti -S N 2′ elimination in the presence of an N-activator to provide a dearomatized tertiary boronic ester. Interception of this dearomatized intermediate with a dienophile leads to stereopredictable cycloaddition reactions to generate highly complex three-dimensional boron-containing molecular structures. When enantioenriched α-methyl-substituted benzylamines are employed, the corresponding cycloaddition adducts are formed with excellent enantiospecificities.