Olefin metathesis is established as a remarkably valuable synthetic tool in current organic chemistry. We report here total synthesis of natural products using sequential olefin metathesis reactions. The one-pot ring-opening/cross/ring-closing metathesis (ROM/CM/RCM) reaction has been developed, allowing for the concise construction of the oxygen-bridged 1,3-cyclooctadiene framework from an oxanorbornene derivative and 1,3-butadiene. The ROM/CM/RCM product was converted into (+)-mycoepoxydiene, (−)-1893A, and (+)-1893B. Furthermore, the ring-opening/ring-closing metathesis (ROM/RCM) of cyclobutenecarboxylate derivatives has been developed as a novel method for access to γ-butenolides. The enantioselective total synthesis of (+)-clavilactone A and (−)-clavilactone B was achieved by the use of this reaction (ROM/RCM).