Synthetic applications of arenetricarbonylchromium(0) complexes: the synthesis of polyfunctionalised thiophenes

Abstract

Lithiation of thiophenetricarbonylchromium(0) complexes with butyllithium occurs preferentially at C-2/5 but when these are blocked, 3/4 lithiation is facile. Combinations of a bulky silyl (Prⁱ₃Si or Bu^tMe₂Si) blocking group at C-2/5 and remote lithiation/electrophilic quench of C-3/4 followed by desilylation/lithiation/electrophilic quench allowed the synthesis of 2,3-, 2,3,5- and 2,3,4,5-polysubstituted thiophene complexes and their derived free thiophenes.