An efficient and versatile copper-catalyzed intermolecular radical [3+2] annulation
of thioamides with azobisisobutyronitrile (AIBN) is described. This two-component
copper(II)-catalyzed transformation is achieved in one pot via cascade formation of
C–S/C–N bonds through cyclization of an in situ generated N,S-acetal intermediate derived from a β-ketothioamide. This operationally simple method
allows direct access to synthetically demanding thiazolidin-4-ones in good to excellent
yields containing diverse functional groups of different electronic and steric nature.
The readily available reaction partners, the avoidance of expensive/toxic reagents
and a gram-scale synthesis are additional attributes of this strategy. AIBN plays
a dual role as a radical initiator and an unusual source of a two-carbon coupling
partner. Notably, the products possess Z stereochemistry with regard to the exocyclic C=C double bond at position 2 of the
thiazolidine ring.
Key words
β-ketothioamides - AIBN - domino annulation - one-pot reaction - 1,3-thiazolidin-4-ones
