The treatment of chloranil (I) with alkali and 2-mercaptoethanol resulted not only in replacement of the chlorine atoms but also in reduction to form 2,3,5,6-tetrakis(β-hydroxyethylmercapto)-1,4-hydroquinone (II). The conditions for the preparation of 2,3,5,6-tetrakis(β-chloroethylmercapto)-1,4-hydroquinone (III) from II differed from those required for the preparation of a lower-melting compound (IV) from II by such a narrow margin that exact control of temperature and concentration were necessary in order to avoid erratic behavior in the preparation. The structure of the lower-melting compound has been established as 2,3-dihydro-5,7,8-tris(β-chloroethylmercapto)-6-hydroxy-1,4-benzoxathiin (IV) by analyses and cyclization reactions. The treatment of 2,3-dichloro-1,4-naphthoquinone (VIII) with 2-mercaptoethanol yielded 2,3-bis(β-hydroxyethylmercapto)-1,4-naphthoquinone (IX) and not the quinol as was the case with chloranil. The quinone (IX) could not be converted to 2,3-bis(β-chloroethylmercapto)-1,4-naphthoquinone by treatment with hydrogen chloride because under these conditions only 1,4-oxathio-5,10-anthraquinone (X) was formed. A mechanism for the formation of X which involves intramolecular addition, elimination, and cyclization is described.
Axial Chirality Beyond Atropisomerism: Allenes and Related Compounds