The highly stereoselective total synthesis of the phytoalexin (+/-)-lubiminol (1) has been accomplished. The synthesis relies on three pivotal transformations: (1) a conjugate addition-cyclization reaction to prepare a highly functionalized 2-carbomethoxycyclopentenone as a photocycloaddition substrate, (2) a double diastereoselective intramolecular photocycloaddition for a stereoselective intramolecular photoaddition reaction which establishes the central quaternary spirocenter, and (3) the transformation of the photoadduct into the required spiro[5.4]decane through a radical fragmentation-rearrangement reaction.