A vinylogous pinacol rearrangement, involving an intramolecular 1,4-migration of the bulkythienothienyl substituent and a marked change of the crystal structure, was thermally induced in the solid statefor thienothienyl-substituted 9,10-dihydroxy-9,10-dihydroanthracenes,
1 and
3~
8. When heated over 180 to~240
C, these crystals were transformed quantitatively, accompanying dehydration, to crystals of the anthronederivatives without wetting or melting. Diol
8, which bears two isomeric thienothiophene rings, afforded onlya single anthrone product. Compounds
1 and
8 formed a mixed crystal and its thermally induced reactionyielded two anthrone products that were attributable to intramolecular migration but afforded no anthronederivative having the two substituents possible for the intermolecular combination. These results, along withthe X-ray crystal structure of the mixed crystal, demonstrate that the rearrangement in the solid state proceedsintramolecularly. The 1,4-pinacol type rearrangements were also induced, along with the
cis-
trans isomerization,by cogrinding the diols with
p-toluenesulfonic acid in a mortar at room temperature. The intramolecularity ofthe rearrangement was again proved by the use of the mixed crystal. The intervention of the carbocation in thesolid-state grinding was ascertained by the UV/vis spectra. The time courses of the product distributions showeddiscrete profiles between the
trans and
cis diols,
1 and
3, respectively; for the
trans diol
1, fast isomerizationto the
cis isomer and consecutive formation of the rearranged product via the
cis isomer were observed. Onthe basis of these observations, the solid-state 1,4-rearrangement was deduced to occur preferentially via the
cis configuration of the dihydroxy groups.