Synthesis and reactions of hydrazine trifluoroborate salts

We report a new class of hydrazine trifluoroborate salts that undergo chemoselective reactions to deliver a range of new functionalized building blocks for organic synthesis. In particular, we show that a wide range of pyrazole N-methylboronates can be prepared by condensation reactions with 1,3-dicarbonyl compounds and conjugated ynones with high regiocontrol. Finally, the synthetic potential of these pyrazole derivatives is demonstrated by SEAr, three-component alkyl Petasis Boron-Mannich reaction, and through the synthesis of palovarotene analogs.