Trans-cyclization products were selectively formed from C-6-substituted acetoxy-octadienes only via Ni(0) catalysis (1→2) and from C-4-substituted analogs under Pd(0)- and Ni(0) catalysis (7, 8→9). C-5-Substituted precursors gave mixtures of diastereoisomers. Nickel(0) catalyzed allylation/methoxycarbonylation of iodo diene 11 afforded 2-oxa-bicyclo[3.3.0]octanone 12 with highly diastereoselective generation of three stereogenic centers.