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

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