Taming of Furfurylidenes by Chiral Bismuth-Rhodium Paddlewheel Catalysts. Preparation and Functionalization of Optically Active 1,1-Disubstituted (Trifluoromethyl)cyclopropanes

Although 2-furyl-carbenes (furfurylidenes) are prone to instantaneous electrocyclic ring opening, chiral [BiRh]-paddlewheel complexes empowered by London dispersion allow (trifluoromethyl)furfurylidene metal complexes to be generated from a bench-stable triftosylhydrazone precursor. These reactive intermediates engage in asymmetric [2+1] cycloadditions and hence open entry into valuable trifluoromethylated cyclopropane or -cyclopropene derivatives in optically active form, which are important building blocks for medicinal chemistry but difficult to make otherwise. 1,1-Disubstituted (trifluoromethyl)cyclopropanes represent bioisostereres of tert-butyl groups of improved metabolic stability; they are on high demand in medicinal chemistry but difficult to make in optically active form. A new approach, which engages a bench-stable carbene source in asymmetric cyclopropanation catalyzed by a [BiRh] paddlewheel complex, opens ready access to compounds of this type.image