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.