Transition-metal-catalyzed formation of trans alkenes via coupling of aldehydes.

[reaction: see text] Rh(2)(OAc)(4) catalyzed the formation of exclusively trans fluorinated alkenes from aldehydes and pentafluorobenzaldehyde tosylhydrazone salts, which were readily prepared from pentafluorobenzaldehyde using the Bamford-Stevens reaction. A series of pentafluorophenyl-containing alkenes were synthesized from aldehydes in moderate to good yields under mild reaction conditions in a one-pot reaction. It is the first report of coupling two different aldehydes to form exclusively trans alkenes.