Chiral ruthenium porphyrins

In 1997 after the introduction of Ru Pybox catalysts, chiral ruthenium porphyrin derivatives were found by three groups to be effective catalysts for ACP... 

Some examples of asymmetric epoxidations of alkenes using chiral ruthenium porphyrins have been reported for example, the previously reported D4-sym-metrical chiral ruthenium porphyrin complex Run(D4-Por )(CO)(MeOH) [58], which produced (R)-styrene oxide in 57% ee with Cl2PyNO as a donor, was readily converted into the dichloro derivative A [59] (Fig. 11). This di-chlororuthenium porphyrin gave (R)-styrene oxide in 69% ee using Cl2PyNO and was highly active (875 TON in 1.5 h). The use of unsubstituted pyridine N-oxide or NMO as oxidants resulted in low substrate conversions as well as... 

A ruthenium porphyrin complex immobilized in a polymer can be used for catalytic epoxidation with 2,6-dichloropyridine N-oxide [112], Nitrous oxide (N2O) can be also used as oxidant for the epoxidation of trisubstituted olefins in the presence of ruthenium porphyrin catalyst [113], Asymmetric epoxidations have been reported using chiral ruthenium porphyrin complexes 35 [114], 36 [115], and 37 [116] (Eq. 3.62). 

Another type of polymer-supported chiral catalyst for asymmetric cyclopropanation was obtained by electropolymerization of the tetraspirobifluorenylporphyrin ruthenium complex [143]. The cyclopropanation of styrene with diazoacetate, catalyzed by the polymeric catalyst 227, proceeded efficiently at room temperature with good yields (80-90%) and moderate enantioselectivities (up to 53% at -40 °C) (Scheme 3.75). PS-supported versions of the chiral ruthenium-porphyrin complexes 231 (Scheme 3.76) were also prepared and used for the same reaction [144]. The cyclopropanation of styrene by ethyl diazoacetate proceeded well in the presence of the polymeric catalyst to give the product in good yields (60-88%) with high stereoselectivities (71-90% ee). The highest ee-value (90%) was obtained for the cyclopropanation of p-bromostyrene. 

Another very good chiral Ru(II) catalyst for the asymmetric cyclopropanation of styrene with ethyl diazoacetate was recently reported [50,51 ]. The chiral ruthenium-porphyrin 37 was found to provide optically active phenylcyclopro-pane derivatives with a very high catalyst turnover number. A 96 4 transxis ratio of products was obtained with styrene and in the presence of only 0.05 mol % of the catalyst 37. The ee of the trans isomer was 91%, Eq. (13). Similar results with high transxis selectivities and high enantioselectivities for the trans product have also been found with other substituted styrenes. 

Very recently, Simmonneaux has reported that a chiral ruthenium-porphyrin complex is an active catalyst for cyclopropanation of styrene, but the corresponding cyclopropanes were produced with low to moderate enantiomeric excesses [52]. 

Gross et al. reported the first use of a chiral ruthenium porphyrin Ru"(L,)(CO) as a catalyst for styrene epoxidation . Chiral ruthenium porphyrin systems have also been reported by Che et a/. . The utilization of another chiral ruthenium porphyrin, Ru"(L2)(CO) as a catalyst for enantioselective epoxidation of olefins with 2,6-dichloropyridine A-oxide has been described by Berkessel and Frauenkron ". The highest enantiomeric excesses of the oxiranes were obtained in the epoxidation of tetrahydronaphthalene and styrene, 77% and 70% ee, respectively, with high jdelds (up to 88%). Terminal aliphatic olefins and tra 5-disubstituted olefins, represented by 1-octene and rraw-stilbene, were sluggish substrates and gave low ee s. The epoxidation of tetrahydronaphthalene with iodosylbenzene catalyzed by Ru(II)(L2)(CO) produced only 52% ee... 

Berkessel, A. and M. Frauenkron (1997). Catalytic asymmetric epoxidation with a chiral ruthenium porphyrin and N-oxides. J. Chem. Soc., Perkin Trans. 16(1), 2265-2266. 

Another innovation involves the preparation of chiral ruthenium porphyrins of type 28, readily available from the reaction of pyrrole with enantiopure aldehydes (e.g., 26), as catalysts for the asymmetric epoxidation of unfunctionalized olefins. Using 2,6-dichloropyridine A-oxide as a terminal oxidant, good yields and enantioselectivities were observed <97JCS(P1)2265>. 

In 1999, Che and co-workers designed and synthesized a D4-symmetric chiral ruthenium porphyrin complex C31. With this catalyst, hydroxylation reactions occurred smoothly at the benzylic positions (Scheme 1.64). In this way, secondary alcohols 161 can be prepared with up to 76% ee from the simple ethylbenzene derivatives 160. It was postulated that the production of enantioenriched products 161 may arise from the preferential collapse of the benzylic radical on the pro-S face versus the pro-R face in the oxygen atom rebound step. 

There has also been a renewal of interest in reactions catalyzed by ru-thenium(II) porphyrin complexes, simultaneously with the development of new chiral ruthenium porphyrins [175-178]. Although these reactions focus mainly on asymmetric epoxidation of olefins [179,180], in some cases asymmetric cyclopropanations were very successful As a recent example, the intermolecular cyclopropanation of styrene and its derivatives with ethyl diazoacetate afforded the corresponding cyclopropyl esters in up to 98% ee with high trans/cis ratios of up to 36 and extremely high catalyst turnovers of up to 1.1 X 10 [140]. The structure of the metalloporphyrin is given in Fig. 2. Asymmetric intramolecular cyclopropanations were also reported with the same catalyst [140]. hi this case, the decomposition of a series of aUyhc diazoacetates afforded the cyclopropyl lactones in up to 85% ee. Both the inter-and intramolecular cyclopropanation were proposed to proceed via a reactive chiral ruthenium carbene intermediate. The enantioselectivities in these processes were rationahzed on the basis of the X-ray crystal structures of closely related stable chiral carbene complexes obtained from the reaction of the chiral complex with N2CPh2 and N2C(Ph)C02CH2CH = CH2. 

Optically active ruthenium porphyrins have also been recently reported [184]. It was decided to target porphyrins bearing spirobifluorenyl groups to allow polymerization and chiral groups for asymmetric induction, as monomers (Scheme 16). As a second example of carbene transfer catalyzed by chiral ruthenium porphyrin polymers, intramolecular cyclopropanation of trans-cinnamyl diazoacetate (Scheme 17) was found to proceed with good enantios-electivity (85%) and high product turnover munbers [186]. 

The first ruthenium porphyrin-catalyzed intramolecular carbenoid C - H insertion to afford selectively cis-2,3-disubstituted-2,3-dihydroergocornine using tosylhydrazone salts as the carbene source was reported by Zheng et al. [192]. This general strategy was applied in natural product synthesis to provide a route to the total synthesis of racemic epi-conocarpan. Enantio-selective synthesis of 2,3-dihydrobenzofurans was also achieved by a similar route using chiral ruthenium porphyrins as catalysts for this interesting carbon-carbon bond formation [193]. Recently, it was found that dinuclear fx-oxo osmium porphyrins are able to catalyze intermolecular carbene insertion into C - H bonds in cyclohexene [153]. 

Zhang JL, Liu YL, Che CM (2002) Chiral ruthenium porphyrin encapsulated in (ndeted mesoporous molecular sieves (MCM-41 and MCM-48) as catalysts for asymmetric alkene epoxidation and cyclopropanation. Chem Common 23 2906-2907... 

Ferrand Y, Le Maux P, Simonneaux G (2004) Highly enantioselective synthesis of cyclopropylphosphonates catalyzed by Chiral Ruthenium Porphyrins. Org Lett 6 3211-3214... 

Le Maux P, Bahri H, Simonneaux G (1991) Moleeular leeognition of racemie phosphines by a chiral ruthenium porphyrin. J (Them Soe (Them Commun 19 1350-1352... 

Simonneaux and coworkers reported that chiral ruthenium porphyrin 270 was used for the asymmetric cyclopropanadon of diisopropyl diazomethylphosphonate [189] or... 

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