Transition-Metal-Catalyzed Cyclopropanation of Nonactivated Alkenes in Dibromomethane with Triisobutylaluminum

The cyclopropanation of nonactivated alkenes with inexpensive triisobutylaluminum (TIBA), in dibromomethane as solvent and reagent, is efficiently catalyzed by FeCl3 at ambient temperature. Catalytic amounts of Cu-I salts, CpTiCl3, and [CpFe(CO)(2)](2) are similarly effective. 2-Methylpropane, generated after quench of excess TIBA can be trapped, and excess dibromomethane can be recycled, which makes the method industrially applicable. Solvent-free DIBAH or TIBA reduction of unsaturated carbonyl compounds, followed by in situ TIBA cyclopropanation of the unsaturated aluminum alcoholates in dibromomethane give cyclopropyl alkanols. Dienols such as geraniol, linalool or nor-radjanol are selectively cyclopropanated in their distal position, which allows the synthesis of flavor and fragrance compounds such as Delta-citral, cis-javanol, and 7-methyl-georgywood. Uncontrollable exothermic events are avoided due to relatively low reaction temperatures made possible by the catalysts and by the addition mode of the reagents.([1])