Chiral Dirhodium(II) Catalysts with Ortho-Metalated Arylphosphine Ligands:  Synthesis and Application to the Enantioselective Cyclopropanation of α-Diazo Ketones

Enantiomerically pure dirhodium(II) complexes with orthometalated p-substituted aryl phosphines have been shown to be enantio-and diastereoselective in the cyclopropanation of styrene by ethyl diazoacetate. Enantioselectivities up to 91% and diastereoselectivities up to 90% are observed for ethyl cis-2-phenylcyclopropanecarboxylateThe design of new chiral catalysts to induce enantiocontrol in carbene transfer reactions is presently a subject of interest. [1][2][3] The intermolecular cyclopropanation reaction of styrene, 1, with ethyl diazoacetate is frequently used as a model reaction to measure the stereo-and enantioselectivity of the new catalyst (Scheme 1).Chiral copper catalysts, 4-8 especially those with bis-oxazoline ligands, have been found to induce the highest levels of enantiocontrol. Thus, enantioselectivities up to 99% for ethyl 2-phenylcyclopropanecarboxylates have been obtained in the cyclopropanation of styrene with ethyl diazoacetate catalyzed by Cu catalysts. Ruthenium catalysts have also produced high level of enantiocontrol in the cyclopropanation of olefins, 9 but their carbenoids are less reactive than those of copper. In general, chiral dirhodium(II) catalysts do not provide high selectivities. 10 Dirhodium(II) catalysts of general formula Rh 2 (O 2 CR) 2 (PC) 2 , containing two ortho-metalated aryl phosphines (PC) in a head to tail arrangement, 11 (Figure 1), have backbone chirality and they can be isolated as pure enantiomers by conventional resolution methods. 12 We have recently reported some of these dirhodium(II) catalysts as the most enantioselective among dirhodium(II) catalysts, giving enantioselectivities up to 91% and up to 87%, for ethyl cis-and trans-2-phenylcyclopropanecarboxylate, respectively. 13 However, these catalysts induce low diastereoselectivities, about 60:40 or lower.According to the transition state model proposed for the cyclopropanation reaction of styrene catalysed by enantiomers of Rh 2 (O 2 CR) 2 (PC) 2 , 13 the presence of bulky substitutents on the metalated ring might improve the diastereocontrol of the catalyst. In order to probe such hypothesis we have studied four dirhodium(II) catalysts with different substituents in the para positions of the aryl groups. These catalysts are represented in Fig. 1.Catalysts 5 and 7 were prepared by standard methods 14 from the reaction of rhodium tetraacetate and the corresponding phosphines.Catalyst 6 was prepared according to the method reported in the literature. 13 We now report the catalytic results obtained in the cyclopropanation of styrene with ethyl diazoacetate using catalysts 5-7 following the procedure described in ref. 13. These results are compared in Table 1 with those previously reported using catalyst 4.As indicated in Fig. 1, all these catalysts contain different groups in the para position of all the aryl groups of the phosphine. The influence of the substituents on the diastereoselectivities of the cyclopropanation reaction is clear, increasing with the size of the substituent Br v Me 3 C v Me 3 Si, w...

show abstract

“…2, placing the ester group at the less sterically demanding quadrant in the neighbourhood of the carboxylate ligands, will be favored compared to the opposite orientation B 1 . The high enantiocontrol observed for these orthometalated rhodium(II) catalysts was previously been attributed 13 to a discrimination between the cyclometalation pathways resulting from A 1 and B 1 intermediates.…”

mentioning

confidence: 78%

“…13 We now report the catalytic results obtained in the cyclopropanation of styrene with ethyl diazoacetate using catalysts 5-7 following the procedure described in ref. 13. These results are compared in Table 1 with those previously reported using catalyst 4.…”

mentioning

confidence: 99%

“…12 We have recently reported some of these dirhodium(II) catalysts as the most enantioselective among dirhodium(II) catalysts, giving enantioselectivities up to 91% and up to 87%, for ethyl cis-and trans-2-phenylcyclopropanecarboxylate, respectively. 13 However, these catalysts induce low diastereoselectivities, about 60:40 or lower.…”

mentioning

confidence: 99%

“…According to the transition state model proposed for the cyclopropanation reaction of styrene catalysed by enantiomers of Rh 2 (O 2 CR) 2 (PC) 2 , 13 the presence of bulky substitutents on the metalated ring might improve the diastereocontrol of the catalyst. In order to probe such hypothesis we have studied four dirhodium(II) catalysts with different substituents in the para positions of the aryl groups.…”

mentioning

confidence: 99%

See 2 more Smart Citations

Enantio‐ and Diastereocontrol in Intermolecular Cyclopropanation Reaction of Styrene Catalyzed by Dirhodium(II) Complexes with Bulky ortho‐Metalated Aryl Phosphines.

Estevan

¹

,

Lahuerta

²

,

Lloret‐Fillol

³

et al. 2005

Self Cite

View full text Add to dashboard Cite

Enantiomerically pure dirhodium(II) complexes with orthometalated p-substituted aryl phosphines have been shown to be enantio-and diastereoselective in the cyclopropanation of styrene by ethyl diazoacetate. Enantioselectivities up to 91% and diastereoselectivities up to 90% are observed for ethyl cis-2-phenylcyclopropanecarboxylateThe design of new chiral catalysts to induce enantiocontrol in carbene transfer reactions is presently a subject of interest. [1][2][3] The intermolecular cyclopropanation reaction of styrene, 1, with ethyl diazoacetate is frequently used as a model reaction to measure the stereo-and enantioselectivity of the new catalyst (Scheme 1).Chiral copper catalysts, 4-8 especially those with bis-oxazoline ligands, have been found to induce the highest levels of enantiocontrol. Thus, enantioselectivities up to 99% for ethyl 2-phenylcyclopropanecarboxylates have been obtained in the cyclopropanation of styrene with ethyl diazoacetate catalyzed by Cu catalysts. Ruthenium catalysts have also produced high level of enantiocontrol in the cyclopropanation of olefins, 9 but their carbenoids are less reactive than those of copper. In general, chiral dirhodium(II) catalysts do not provide high selectivities. 10 Dirhodium(II) catalysts of general formula Rh 2 (O 2 CR) 2 (PC) 2 , containing two ortho-metalated aryl phosphines (PC) in a head to tail arrangement, 11 (Figure 1), have backbone chirality and they can be isolated as pure enantiomers by conventional resolution methods. 12 We have recently reported some of these dirhodium(II) catalysts as the most enantioselective among dirhodium(II) catalysts, giving enantioselectivities up to 91% and up to 87%, for ethyl cis-and trans-2-phenylcyclopropanecarboxylate, respectively. 13 However, these catalysts induce low diastereoselectivities, about 60:40 or lower.According to the transition state model proposed for the cyclopropanation reaction of styrene catalysed by enantiomers of Rh 2 (O 2 CR) 2 (PC) 2 , 13 the presence of bulky substitutents on the metalated ring might improve the diastereocontrol of the catalyst. In order to probe such hypothesis we have studied four dirhodium(II) catalysts with different substituents in the para positions of the aryl groups. These catalysts are represented in Fig. 1.Catalysts 5 and 7 were prepared by standard methods 14 from the reaction of rhodium tetraacetate and the corresponding phosphines.Catalyst 6 was prepared according to the method reported in the literature. 13 We now report the catalytic results obtained in the cyclopropanation of styrene with ethyl diazoacetate using catalysts 5-7 following the procedure described in ref. 13. These results are compared in Table 1 with those previously reported using catalyst 4.As indicated in Fig. 1, all these catalysts contain different groups in the para position of all the aryl groups of the phosphine. The influence of the substituents on the diastereoselectivities of the cyclopropanation reaction is clear, increasing with the size of the substituent Br v Me 3 C v Me 3 Si, w...

show abstract

Catalytic, Asymmetric, Intramolecular Carbon–Hydrogen Insertion

Doyle

¹

,

Liu

²

,

Ratnikov

³

2012

View full text Add to dashboard Cite

The insertion of a chiral‐ligated metal carbene into an aliphatic C‐H bond to construct a carbon‐carbon bond imparts asymmetry into the resultant molecule to form enantiomerically enriched lactones, lactams, and cycloalkane derivatives and returns the chiral‐ligated metal to its catalytically active state. Insertion is favored by electron‐donating groups adjacent to the C‐H bond that undergoes insertion, and is disfavored by electron‐withdrawing groups. Chiral dirhodium(II) carboxamidates have proven to have the greatest breadth of high selectivities, but other classes of catalysts are selective in specific cases. Although there are examples of iodonium ylides as reactants, diazo compounds are the reactants of choice for these reactions. Diazocarbonyl compounds, especially diazoacetates and diazoacetamides, have reactivities and selectivities that are most suitable for high product yields and high stereoselectivities. This reaction is optimally designed for the formation of five‐membered ring compounds using diazoacetates and diazoacetamides and of four‐membered ring products with constrained diazoacetamides. Access to lignan lactones, baclofen, deoxyxylolactone, and rolipram, among others, exemplify the efficiencies of this methodology relative to other synthetic approaches.

show abstract

Chiral Dirhodium(II) Catalysts with Ortho-Metalated Arylphosphine Ligands: Synthesis and Application to the Enantioselective Cyclopropanation of α-Diazo Ketones

Cited by 56 publications

References 37 publications

Enantio- and diastereocontrol in intermolecular cyclopropanation reaction of styrene catalyzed by dirhodium(ii) complexes with bulky ortho-metalated aryl phosphines

Enantio- and diastereocontrol in intermolecular cyclopropanation reaction of styrene catalyzed by dirhodium(ii) complexes with bulky ortho-metalated aryl phosphines

Enantio‐ and Diastereocontrol in Intermolecular Cyclopropanation Reaction of Styrene Catalyzed by Dirhodium(II) Complexes with Bulky ortho‐Metalated Aryl Phosphines.

Catalytic, Asymmetric, Intramolecular Carbon–Hydrogen Insertion

Contact Info

Product

Resources

About