A four-step synthesis of benzo- and naphthothiophenes that have biological importance
and application in material science was integrated into a one-pot reaction by using
silica gel-supported acid and base reagents, NaHSO4/SiO2 and Na2CO3/SiO2. The supported reagents provided acid and base environments on the surface of the
supports without neutralization and worked separately in the same medium. The four-step
reaction comprises (i) deacetylation of 3-halo-2,4-pentanediones to α-halo ketones,
(ii) deacetylation of S-aryl thioacetates to arenethiols, (iii) coupling of α-halo ketones and arenethiols
to give α-sulfanyl ketones, and (iv) cyclization of sulfanyl ketones to benzo- and
naphthothiophenes. The steps (i) and (iii) proceeded by Na2CO3/SiO2, and (ii) and (iv) by NaHSO4/SiO2. The four-step reaction proceeded efficiently by introduction of starting materials
and reagents in a single reaction vessel. The starting materials were very easy to
handle and unpleasant smell of aryl thiols that were used in conventional methods
could be avoided. Novel thirty-nine benzo- and naphthothiophenes were synthesized
by this method in excellent to fair yields.
Key words
benzothiophenes - one-pot synthesis - 3-halo-2,4-pentanediones -
S-aryl thioacetates - silica-gel-supported reagents