strained carbon skeletons by ring-closing olefin metathesis (RCM) was investigated. With well-designed diene 4, RCM was found to be applicable to the formation of a highly strained inside−outside bicyclo[4.4.1]undecane skeleton of ingenol, a bioactive diterpenoid, and formal total synthesis of optically active ingenol (1) was achieved. The key features of this synthesis are construction of an A-ring