Divergent insertion reactions of Pt-carbenes generated from [3+2] cyclization of platinum-bound pyrylliums

The divergent insertion reactions of Pt-Carbenes generated from [3+2] cyclization of platinum-bound pyrylliums was studied. The enynals 7 bearing an olefinic pendant were successfully cyclized through Huisgen-type cycloaddition to the tetracyclic Pt-carbene complex B which would undergo insertion into a C-H bond of the β-position to afford the fused cyclopropanes 8 which are otherwise not accessible. The experiment included a 5ml test tube filled with o-alkynylbenzaldehyde 7a, PtCl₂ and dry toluene which were allowed to react at 0°C and the reaction mixture was kept under argon atmosphere. The preliminary results using molecular modeling show that trans-B is less likely to be formed due to steric hindrance between the incoming double bond and the Zgroup. Several substrates were examined under the preset conditions to explore the scope and limitations of this reaction. The acid catalyzed rearrangement of cyclopropanes 8 smoothly occurred to form the corresponding spiranes 9 with excellent levels of stereoselecivity.