Boron-Containing Enamine and Enamide Linchpins in the Synthesis of Nitrogen Heterocycles

The use of α-boryl enamine
and enamide linchpins in the synthesis
of nitrogen heterocycles has been demonstrated. Boryl enamines provide
ready access to the corresponding α-halo aldehydes, which undergo
regioselective annulation to form borylated thiazoles. A condensation/amidation
sequence converts α-boryl aldehydes into stable α-boryl
enamides without concomitant C → N migration. We also show
that palladium-catalyzed cyclization of α-boryl enamides leads
to synthetically versatile isoindolones. These molecules can be subsequently
used to access polycyclic scaffolds.