Organozirconium-mediated synthetic reactions

Abstract

Transmetalation of organozirconiums into organostannanes and zirconocene-mediated deoxygenation of vinyl epoxides, vinyl acetonides and 2,5-dihydro-furans have been investigated. The reaction of organozirconium compounds, in situ from various substrates, with tributyltin ethoxide afforded versatile organostannanes in good yields. Also, zirconabicycles were generated by the zirconium-promoted bicyclization of diene, enyne and diyne, and they were treated with dibutyltin dimethoxide to afford the corresponding bicyclic organostannanes in good yields. The reaction of vinyl epoxides with dibutylzirconocene would produce conjugated dienes involving the loss of oxozirconocene via deoxygenation of allylzirconocene pathway in good yields. The reaction of vinyl acetonides with dibutylzirconocene afforded conjugated dienes with the retention of the stereochemistry through the sequential process of complexation of olefin unit in vinyl acetonides with dibutylzirconocene, zirconacyclopropane ring fragmentation to the allylzirconium complex and ejection of acetone, and the loss of oxozirconocene in good yields. The reaction of 2,5-dihydrofurans with dibutylzirconocene would produce conjugated dienes via complexation of olefin unit, zirconacyclopropane ring fragmentation, and elimination of oxozirconocene in moderate yields. The zirconocene-mediated reactions of 2,5-dihydrothiophenes proceeded with the loss of sulfidozirconocene providing conjugated dienes. In the case of 2,5-dihydropyrroles, however, the reactions did not proceed.