Polyoxyethanyl a-tocopheryl sebacate

In addition, asymmetric cyclization of the enone 253 could also be performed in water despite the insolubility of the enone. In the presence of nanomicelleforming polyoxyethanyl-a-tocopheryl sebacate (PTS, nonionic vitamin E based surfactant) with excess phenylsilane at 5°C, the cyclized product 254 was obtained in comparable yield and enantiomeric excess (Scheme 113). 

Scarso and Strukul observed that anionic micelles based on sodium dodecyl-sulfate (SDS) efficiently solubilized Pt bis-cationic complexes and ketones in the apolar core of the micelles. This favored the contact between substrate and catalyst and, more importantly, led to a higher steric control of the asymmetric reaction thanks to the more ordered nano-environment present in the micelles compared to bulk organic solvents. Each substrate required the dedicated optimization of the catalyst, the surfactant and the experimental conditions since the distribution of the substrates and catalysts is greatly affected by the kind of surfactant and aggregate considered (Scheme 23.42). Overall, in all the cases tested, an increase in enantioselectivity was observed for the asymmetric BV oxidation of meso-4-substituted cyclohexanones with bis-diphenylphoshinobinaphthyl (BINAP) as the hgand and SDS as the surfactant. A different scenario was present in the kinetic resolution of chiral cyclobutanones or with meso cyclobutanones where an increase of enantioselectivity was observed with the neutral polyoxyethanyl-a-tocopheryl sebacate (PTS) surfactant (Scheme 23.42). 

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