Simple 1, 4-dien-3-ones and 1, 3-dienes react in the presence of BF3⊙ OEt2 via a domino Nazarov electrocyclization/intermolecular [4+ 3]-cycloaddition sequence to furnish keto- bridged cyclooctenes in good yield. Most cases showed high diastereofacial selectivity and/or endo/exo selectivity, and surprising levels of regioselectivity were observed when isoprene was used as the diene partner.