Kinetic Resolution of Acyclic Secondary Allylic Silyl Ethers Catalyzed by Chiral Ketones

Abstract

Kinetic resolution of acyclic secondary allylic silyl ethers by chiral dioxiranes generated in situ from chiral ketones (R)-1 and (R)-2 and Oxone was investigated. An efficient and catalytic method has been developed for kinetic resolution of those substrates with a CCl(3), tert-butyl, or CF(3) group at the alpha-position. In particular, high selectivities (S up to 100) were observed for kinetic resolutions of racemic alpha-trichloromethyl allylic silyl ethers 7 and 9-15 catalyzed by ketones (R)-2. Both the recovered substrates and the resulting epoxides were obtained in high enantiomeric excess. On the basis of steric and electrostatic interactions between the chiral dioxiranes and the racemic substrates, a model was proposed to rationalize the enantioselectivities and diastereoselectivities in the chiral ketone-catalyzed kinetic resolution process.

Recent Advances in Iminium‐Salt‐Catalysed Asymmetric Epoxidation

“…Catalytic Kinetic resolution in asymmetric epoxidation has been observed previously by Sharpless, 103 Jacobsen, 104 Katsuki, 105 Shi 57 and Yang, 107 and is discussed below.…”

“…107 Yang also showed that diastereoselectivities were excellent, with ratios of erythro:threo consistently around 49:1 (Table 23). …”

ChemInform Abstract: Recent Advances in Organocatalytic Kinetic Resolution for the Synthesis of Functionalized Products

“…In 2001, Yang et al reportedt he OCKR of acyclic masked allylic alcohols catalyzed by C 2 -symmetric chiral ketones. [39] Recently, Page et al realized iminium salt catalyzed OCKR in asymmetric epoxidation (Scheme 17). [40] The process involved dihydroisoquinolinium-derived iminium salt catalyst 80,i nw hich racemic 2substituted benzopyrans 81 were resolved through asymmetric epoxidation of the olefinic moiety by using tetraphenylphosphonium monoperoxysulphate (TPPP).…”

Oxidation

“…Some examples of olefins successfully epoxidized by the catalysts 12 are shown below. For the linear substrates shown in Scheme 10.4 epoxidation catalyzed by ketone 5b resulted in the predominant formation of the erythroepoxides (erythro/threo-ratio usually better than 49:1) [28]. In summary, the preparation of these materials (e.g.…”

“…Use of 12a enables reduction of catalyst loading to 1-5% [20]. Chiral ketone catalysts of the Yang-type (5a and 5b, see above) and of the Shitype (10, Scheme 10.2) have been successfully used for kinetic resolution of several racemic olefins, in particular allylic ethers (Scheme 10.4) [28,29]. Some examples of olefins successfully epoxidized by the catalysts 12 are shown below.…”