Enantioselective epoxidation of olefins with chiral metalloporphyrin catalysts

Abstract

The intent of this tutorial review is to cover the recent progress accomplished in iron and manganese porphyrin-catalyzed enantioselective epoxidation of terminal olefins. The literature is covered up to the beginning of 2005. In the first part of the manuscript, we will present the results obtained with simple catalysts in the early eighties, before describing the pickets and strapped series reported more recently. We will also place a special emphasis on the biomimetic approach that oriented most of this research throughout the years. As a conclusion, we will demonstrate that easy-to-prepare porphyrin catalysts should play an important role in the future and should compete with other well-known, successful systems. Among those, the popular titanium tartrate-catalyzed Sharpless-Katsuki asymmetric epoxidation allows the conversion of allylic alcohols to chiral epoxides with high enantiomeric excesses and high conversion. We will also cite the chiral metallosalen complexes independently reported by Jacobsen and Katsuki in 1990. Using manganese-salens, cis-1,2-disubstituted, trisubstituted and some tetrasubstituted olefins are efficiently epoxidized with high enantiomeric excess. However, they suffer from two major drawbacks. They often require low temperature for the epoxidation of monosubstituted (57% ee for styrene at 5 degrees C; 80% at -78 degrees C). More importantly, they proceed with low turnover numbers, TON (TON approximately 40 for styrene). More recently, a new approach involving metal-free chiral dioxiranes was also reported. In some cases, they constitute an interesting alternative to the more common systems previously discussed. Compared to the three pre-cited systems, chiral metalloporphyrins allow the enantioselective epoxidation of unfunctionalized terminal olefins with high enantiomeric excess (>97% ee for styrene) and impressive turnover numbers (>16000) when PhIO is used as oxidant. These results highlight the remarkable potential of porphyrin-based catalysts.

Porphyrins as Catalysts in Scalable Organic Reactions

“…Due to the relevance of cytochrome P-450 mechanism, catalytic epoxidation by iron porphyrins has gained great attention [33]. Since the Groves and co-workers' first report in 1983 [34], several research groups have employed chiral metalloporphyrins [35] to catalyse the oxidation of various organic substrates, and new synthetic routes have been created to improve the catalytic performance of these heterocyclic complexes.…”

Chemical Synthesis and Medicinal Applications of Glycoporphyrins

“…While catalytic applications have no direct relevance for biomedical uses such studies do indicate the degree to which porphyrin-conjugates can be fine-tuned and modified for a specific purpose, such as substrate or receptor binding. The catalytic ability of metalloporphyrins is well known [402][403][404] and use of glycoporphyrins might result in either water soluble catalysis and/or enhance catalyst selectivity. Such studies can also be of relevance for understanding natural porphyrin based oxidations.…”

Asymmetric catalysis using iron complexes – ‘Ruthenium Lite’?

“…The developments in this area of chiral strapped porphyrins, 60 not 30 only of iron but also containing Mn and Ru, has recently been summarised in a detailed review. 61 In other early work, Jacobsen described the use of combinatorial methods to discover an optimised catalyst for iron-catalysed epoxidation of tran--methylstyrene. 62 35 Following a process of split-mix bead functionalisation and testing with a range of metals, several FeCl 2 complexes 55 and 56 emerged as sucessful in the epoxidation reaction using aqueous hydrogen peroxide (Figure 19).…”