New ferrocenyl ligands for the asymmetric Heck reaction and the development of catalysts for hydroxyl-directed epoxidation.

摘要

The palladium catalyzed arylation and alkenylation of alkenes, Heck reaction, is a powerful carbon-carbon bond forming reaction. We have investigated a series of phosphinoferrocenyl oxazoline ligands in the asymmetric Heck reaction and found that the tert-butyl substituted oxazoline ligand was optimal in the reaction of phenyl triflate and 2,3-dihydrofuran, providing the highest yield and highest ee.; The scope of the reaction was then studied. The tert-butyl substituted oxazoline ligand provided high levels of asymmetric induction with various aryl triflates and endocyclic alkenes (up to 98.9% ee). Unfortunately the ferrocenyl derived ligand was less active than the corresponding phenyl derived ligand. In an effort to understand this effect, we synthesized substituted phosphine oxazoline ligands bearing different groups on the phosphine. These ligands were screened in the reaction of phenyl triflate with 2,3-dihydrofuran. Simple aryl substituents were found to have little effect on the ee of the product, however the para-trifluoromethylphenyl substituted phosphine ligand provided the product in higher yield over the parent system.; Analysis of the distribution of the products in the reaction of naphthyl triflate with 2,3-dihydrofuran allowed us to determine the enantioselection of the Pd-π complex formed after the initial oxidative addition step. The diphenyl (phosphinoferrocenyl) oxazoline ligand provides significantly higher levels of enantioselection over BINAP, 95% vs 63%.; We have also studied the development of catalysts bearing spatially distinct binding and catalytic sites. We describe studies directed towards the development of hydroxyl-directed epoxidation catalysts, where a formyl group could act as a hydroxyl binding site. Initial investigations focused on the synthesis of a suitably derivatized Mn-salen ligand. We describe how a modified Duff reaction can be used to simultaneously introduce two formyl groups. Unfortunately the use of this catalyst in the epoxidation of cinnamyl alcohol provided both the desired epoxy alcohol as well as the enal.; We also describe the synthesis of a chiral pyridine derived ligand bearing a phenyl ketone that could also act as a binding site. Unfortunately this ligand did not provide any appreciable levels of asymmetric induction in the vanadium or molybdenum catalyzed epoxidation of cinnamyl alcohol and cis-2-hexenol.