Small-Ring Compounds. XVII. 2-Hydroxy-3-phenyl-2-cyclobutenone and Related Substances

1,1,2-Trifluoro-2-chloro-3-phenylcyclobutane (I ) undergoes dehydrohalogenation with one mole of ethanolic potassium hydroxide and is converted to 1,1,2-trifluoro-3-phenyl-2-cyclobutene (II). With excess ethanolic potassium hydroxide, I, II or 1,1,2,2-tetrafluoro-3-phenylcyclobutane (IV) yield 1,1-difluoro-2-ethoxy-3-phenyl-2-cyclobutene (III). Hydrolysis of III in 92% sulfuric acid affords 2-ethoxy-3-phenyl-2-cyclobutenone (V) which is rather more stable toward acid hydrolysis than ordinary vinyl ethers. Treatment of I with excess potassium-butoxide in t-butyl alcohol yields 1.1-difluoro-2-t-butoxy-3-phenyl-2-cyclobutene (VI) which, on acid hydrolysis, gives 2-hydroxy-3-phenyl-2-cyclobutenone (VII). The pK_A of VII was found to be 3-4 units lower than the pK_A's of 2-hydroxy-2-cyclopentenone and 2-hydroxy-2-cyclohexenone.