Studies on cavity shaped polycyclic thiaarenes: Short and efficient synthesis of 2,12-dimethylanthra[1,2-b][8,7-b]bisthiophene and anthra[1,2-b]thiophene

A short, efficient and high yielding synthesis of anthra[1,2-b][8,7-b]bisthiophene (5) and anthra[1,2-b]thiophene (12) is described. Compound 5 has been synthesised by condensation of methyl thioglycolate with the bis-chloroaldehyde 1 to give the 2,10-dicarbomethoxyanthra[1,2-b][8,7-b]bisthiophene (2). Subsequent hydrolysis of the diester followed by decarboxylation of the resulting diacid 3 produces 4,5,7,8-tetrahydroanthra[1,2-b][8,7-b]bisthiophene (4) which is aromatized with DDQ to furnish compound 5. Following the similar sequence of reaction on the chloroaldehyde 8 anthra[1,2-b]thiophene (12) has been synthesised. Compound 5 on further methylation with n-BuLi and MeI results in the formation of the dimethyl derivative 6.