Synthesis of Fluorinated α-Pyrans

Significance

Based on previous work showing that F-vinyl and F-aryl copper reagents add to hexafluoro-2-butyne to stereospecifically provide F-dienylcopper or F-arylvinylcopper reagents (K. J. MacNeil, D. J. Burton J. Org. Chem. 1993, 58, 4411; M. Yamamoto, D. J. Burton, D. C. Swenson J. Fluorine Chem. 1995, 72, 49), acylation of the F-dienylcopper reagents with acyl ­halides has been carried out to afford the corresponding di­enylketones (T. D. Spawn, D. J. Burton Bull. Soc. Chim. Fr. 1986, 876) which undergo spontaneous cyclization to give pyran derivatives. A sterically hindered dienylketone was observed in solution by ^¹9F NMR. In some cases, protonation of the dienylcopper reagent occurred to yield the reduced diene.