Platinum(II)-Catalyzed Cyclopropanation of Vinyl Arenes and 1,3-Aryl Dienes Employing Aryl Diazirines as Carbene Precursors

PtCl2(NCC6F5)2 catalyzes the reaction of electron-rich vinyl arenes with aryl diazirines in chloroform at 45 °C for 12 h to form 1,2-diarylcyclopropanes in >75% yield with cis/trans selectivity ranging from 3.0 - 10:1. The method is similarly applicable to the cyclopropanation of 1-aryl-1,3-butadienes, albeit with diminished diastereoselectivity (cis/trans = 0.5 - 2.6). Kinetic studies support a mechanism for diazirine to alkene carbene transfer involving nucleophilic attack of diazirine on a platinum bis(vinyl arene) complex followed by C–N oxidative addition, nitrogen extrusion, and addition of the vinyl arene C=C bond across the Pt=C bond of the resulting electrophilic dichloroplatinum carbene complex.