However, there are many exceptions to this sequence depending on the reagents used, as well as steric and electronic effects in the substrate. In addition to peracids, alkaline hydrogen peroxide or hydrogen peroxide together with a Bronsted or Lewis acid like BF3 can also be effective. The migratory tendency can be quite different with different reagents. For example, benzaldehyde gives mostly H migration with KHSO5, mostly Ph migration with H2O2/NaOH, and about equal amounts of both with MCPBA. Electron rich aryl rings migrate preferentially over electron poor ones, and thus the sequence among secondary, aryl, and hydrogen migratory aptitudes can be changed by substituents on the aromatic ring. Vinyl groups migrate comparably to aryl, but the enol ester products are often epoxidized during the reaction.
Chemicals, biochemicals, and strains; analytical methods; specific activity of NOX for the cell-free extract; specific activity of SpEH, BDHA, LDH, and NOX for the lyophilized cell-free extracts; procedure for the hydrolysis of epoxides with (SpEH); data for the oxidation of diols with (BDHA) and (BDHA-NOX); chiral GC and HPLC chromatograms; and 1H NMR spectrum ()
Epoxide synthesis by epoxidation - Organic chemistry
The synthesis of optically pure (+)-ambrisentan has been achieved from 3,3-diphenylacrylate in four steps with 53% overall yield and >99% ee at the >100 g scale without column purification. The chiral epoxide intermediate was prepared via asymmetric epoxidation with a fructose-derived diacetate ketone as catalyst.