Starting from 2-cyclopentenoyl chloride ((RS)- or (S)-8), the racemic as well as the enantiomerically pure (+)-sesquiterpenes longifolene ((±)- and (+)-1, resp.) and sativene ((±)- and (+)-2, resp.) were synthesized efficiently by a sequence of nine and ten steps, respectively. The key sequence 10 → 16 → 3 is the first strategic application of an intramolecular photoaddition/retro-aldolization sequence (intramolecular de Mayo reaction) in organic synthesis.