Hydrogen-Bonding Activation of Gold(I) Chloride Complexes: Enantioselective Synthesis of 3(2)-Furanones by a Cycloisomerization-Addition Cascade.

Enantioselective synthesis of 3(2)-furanones has been achieved using the intermolecular H-bonding activation of gold(I) chloride complexes. A DM-BINAP [()-(+)-2,2'-Bis[di(3,5-xylyl)phoshino]-1,1'-binaphthyl] digold(I) dichloride complex in combination with a sulfonyl squaramide (SOSq) has been identified as the optimal catalytic system. The process involves a 5-- oxa-cyclization followed by stereocontrolled addition of indoles. Interestingly, the soft LAu-Cl activation by H-bonding allowed the recovery of both LAu-Cl and the activator after chromatographic purification.