Kinetic resolution of terminal epoxides

In sharp contrast, Bartoli showed that the (salen) Co catalyst system could be applied to the kinetic resolution of terminal epoxides with unprotected tert-butyl carbamate as nucleophile with extraordinarily high selectivity factors (Scheme 7.40) [72]. Excellent yields and selectivities are also obtained with use of ethyl, Cbz,... 

One way of overcoming these problems is by kinetic resolution of racemic epoxides. Jacobsen has been very successful in applying chiral Co-salen catalysts, such as 21, in the kinetic resolution of terminal epoxides (Scheme 9.18) [83]. One enantiomer of the epoxide is converted into the corresponding diol, whereas the other enantiomer can be recovered intact, usually with excellent ee. The strategy works for a variety of epoxides, including vinylepoxides. The major limitation of this strategy is that the maximum theoretical yield is 50%. 

The hydrolytic kinetic resolution of terminal epoxides catalyzed by the monomer la and dimer lb... 

S,12S)-2,12-Diacetoxytridecane (17) is a component of the female pheromone of pea midges (Contarinia pisi). Kitching synthesized 17 as shown in Scheme 28 by employing Jacobsen s hydrolytic kinetic resolution of terminal epoxides with a (salen)Co(OAc) complex, (S,S)-B [46]. By this reaction bis-... 

M. Tokunaga, J. F. Larrow, F. Kakiuchi, E. N. Jacobsen, Asymmetric Catalysis with Water Efficient Kinetic Resolution of Terminal Epoxides by Means of Catalytic Hydrolysis, Science 1997, 2T7, 936-938, and references cited therein. 

Kim et al. [67], used the self-polymerized heterometallic polymeric salen complexes 26-32 as efficient catalysts for kinetic resolution of terminal epoxides with phenols to give a-aryloxy alcohols in high yields (38-43%) and ee (92-99%) (Scheme 17). These catalysts were recycled up to three times without any loss in their performance. 

Tokimaga, M. Larrow, J. F. Kakiuchi, F. Jacobsen E. N. (1997) Asymmetric catalysis with water Efficient kinetic resolution of terminal epoxides by means of catalytic hydrolysis., Science, 111 936-938. 

Cavazzini, M. Quid, S. Pozzi, G. (2002) Hydrolytic kinetic resolution of terminal epoxides eatalyzed by fluorous chiral Co(salen) complexes. Tetrahedron 58 3943-3949. 

Shepperson, L Cavazzini, M. Pozzi, G. Quici, S. (2004) Fluorous biphasic hydrolytic kinetic resolution of terminal epoxides, J. Fluor. Chem., 125 175-180. 

Annis, D. A. Jaeobsen, E. N. (1999) Polymer supported ehiral Co(salen) complexes synthetie applieations and mechanistic investigations in the hydrolytic kinetic resolution of terminal epoxides., Y. Am. Chem. Soc., 121 4147-4154. 

To investigate the catalytic activity of the materials prepared, hydrolytic kinetic resolution of terminal epoxides such as styrene oxide, 1,2-epoxyhexane, and epi-chlorohydrin was carried out using only water, which acts as a nucleophilic agent... 

Hydrolytic Kinetic Resolution of Terminal Epoxides with Water (Scheme 6.9)... 

This result, caused by the proximity effect between peripheral catalytic sites, can translate into higher or lower catalytic activity of the metallodendrimer in homogeneous catalysis, and is commonly termed the dendritic effect. In the above case, a negative dendritic effect is observed. An interesting example of a positive dendritic effect on catalyst activity was reported by Jacobsen et al. in the hydrolytic kinetic resolution of terminal epoxides by peripherally Co(salen)-substituted PAMAM dendrimers [39]. 

The effect of microwaves on the kinetics and the selectivity of the Cr (salen)-catalyzed asymmetric ring opening of epoxides was investigated by Dioos and Jacobs (2005). It was found that the reaction rate of the Cr (salen)-catalyzed kinetic resolution of terminal epoxides and the asymmetric ring opening (ARO) of meso-epoxides could be increased by three orders of magnitude without impairing the selectivity. 

Schaus, S. E., Brandes, B. D., Larrow, J. F., Tokunaga, M., Hansen, K. B., Gould, A. E., Furrow, M. E., Jacobsen, E. N. Highly Selective Hydrolytic Kinetic Resolution of Terminal Epoxides Catalyzed by Chiral (salen)Colll Complexes. Practical Synthesis of Enantioenriched Terminal Epoxides and 1,2-Diols. J. Am. Chem. Soc. 2002, 124, 1307-1315. 

S. E. Schaus, B. D. Brandes, J. F. Larrow, M. Tokunaga, K. B. Hansen, A. E. Gould, M. E. Furrow, E. N. Jacobsen, Highly selective hydrolytic kinetic resolution of terminal epoxides cataly zed by chiral (salen)Co complexes. Practical synthesis of enantioenriched termmal epoxides and... 

When using (rac)-vinylcyclohexane epoxide as a standard substrate (Scheme 4.24), the dendrimer catalysts exhibited significantly higher catalytic activities in the hydrolytic kinetic resolution of terminal epoxides as compared to the monomer or the dimer catalysts. Among the dendrimer catalysts, the first-generation dendrimer catalyst gave the best results and the efficiency of the catalyst on a per-metal basis was in the following order 4-Co(salen)-PAMAM > 8-Co(salen)-PAMAM > 16-Co(salen)-PAMAM. This dendrimer effect was considered to arise from the restricted conformation imposed by the dendrimer structure, which enhanced the... 

Scheme 5.3 Hydrolytic kinetic resolution of terminal epoxides.

Table 2. Kinetic resolution of terminal epoxides with TMSN3 catalyzed by 1 ...

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