A versatile regio- and stereospecific annulation method - I

The preparation of the title compounds is easily accomplished by cycloaddition of 1,2,3,4-tetrachloro-5,5-dimethoxycyclopentadiene with allylic and homoallylic alcohols yielding tetrachloronorbornene carbinols and their homologues resp., which cyclize under basic conditions by nucleophilic addition to the strained double bond. Dechlorination is achieved by simultaneous or subsequent treatment with sodium in refluxing ethanol. The range and limitations of this reaction sequence are discussed and the dependence of the reaction rate of the intramolecular nucleophilic addition on the structure, the nucleophilicity of the anionic entity and the presence of the chlorine atoms are demonstrated.