The synthesis of fluorinated α-pyrans via fluorinated vinylcopper reagents

Fluorinated vinylcopper reagents were prepared in situ via reaction of fluorinated vinylbromides or iodides with cadmium or zinc powder followed by metathesis with Cu(I)Br. Hexafluoro-2-butyne was then added to the solution of the F-vinylcopper reagent which resulted in a stereospecific syn addition of the F-vinylcopper reagent to the alkyne to provide in situ the corresponding dienylcopper reagent. Subsequent acylation of the dienylcopper reagent gave a dienylketone, which spontaneously cyclized to the 2H-pyran. This methodology provides a useful one flask route to fluorinated 2H-pyrans.