The intramolecular addition of a hydroxyl group to an alkene promoted by Pd(II) leads to an alkyl-Pd intermediate which can undergo CO insertion and cleavage by MeOH. The result is 1,2-alkoxycarbonylation. While in the formation of six-membered rings the 2,6-substituents strongly prefer a cis arrangement, the selectivity in generating 2,5-disubstituted tetrahydrofurans is poor. However, nearby substituents can influence the selectivity, and by proper positioning of large (removeable) groups, both cis-2,5 and trans-2,5 disubstituted isomers can be prepared selectively. In the absence of CO,β-hydride elimination is fast, and a remarkable solvent effect has been observed. In DMSO, the kinetic product is formed very selectively, while in MeCN, for example, the thermodynamic olefin isomer is preferred. These selectivities are tested in a plan for the synthesis of tetronomycin A.
All Science Journal Classification (ASJC) codes
- Chemical Engineering(all)