Cis-Trans Isomerization of Epoxides Catalyzed by Ruthenium(II) Porphyrins

Article abstract of DOI:10.1021/ja00221a021

Bis(tetrahydrofuran)(5,10,15,20-tetramesyitylporphyrinato)ruthenium(II) IITMP(THF)2> and the corresponding p-tolylporphyrin IITTP(THF)2> have been found to catalyze the cis-trans isomerization of epoxides under mild conditions.For β-methylstyrene oxide an equilibrium ratio of 5.4:1 (trans/cis) was achieved with either isomer indicating a free energy difference of 1 kcal/mol.Inhibition of the isomerization by added olefins was observed and attributed to olefin coordination to ruthenium(II). cis-β-Methylstyrene oxide readily formed an adduct with Ru^IITMP(CO), while the trans isomer did not.The isomerization of trans-(1S,2S)-β-methylstyrene oxide gave only cis-(1R,2S)β-methylstyrene oxide.A mechanism for epoxide isomerization involving homolytic cleavage of the C1-O bond to give carbon radical intermediate is proposed.