Atom Efficient Synthesis of Selectively Difluorinated Carbocycles through a Gold(I)-Catalyzed Cyclization

The
intramolecular carbocyclization of difluorinated enol acetals
has been achieved for the first time using gold­(I) catalysis. Difluorinated
enol acetals bearing a pendant alkene group can be cyclized and reduced
in one pot to form fluorinated diol motifs. Alternatively, the cyclization
of terminal alkynes allows for the synthesis of fluorinated pyran
scaffolds. Both cyclization processes can be performed under mild
conditions allowing access to complex products rich in functionality.
The cyclic systems are synthesized concisely (maximum four steps)
from trifluoroethanol, an inexpensive fluorinated feedstock.