Disubstituted aromatic epoxides

One year later, the same authors studied the biohydrolysis of seven differently substituted a-methylstyrene oxide derivatives, including the para-bromo-a-methyl styrene oxide, using ten different EHs [14]. The best results were obtained with the 

Kinetic hydrolytic resolution at high substrate concentration of para-bromo-a-methyl styrene oxide using an enzymatic extract of Aspergillus niger LCP 521. 

8 EPOXIDE HYDROLASES AND THEIR APPLICATION IN ORGANIC SYNTHESIS 

Preparative-scale synthesis of enantiopure para-trifluoromethyl-a-methyl styrene oxide using a partially purified recombinant EH from Aspergillus niger LCP 521 as a biocatalyst. 

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We will describe representative procedures for the epoxidation of a disub-stituted aromatic allylic alcohol (A), a trisubstituted aromatic allylic alcohol (B) and a disubstituted aliphatic allylic alcohol (C). 

The Jacobsen-Katsuki Schiff base Mn complexes (6a and 6b) are the most advanced catalysts for enantioselective epoxidation of double bonds. With the typical reactants, cis disubstituted and trisubstituted aromatic olefins, ee values up to 98% are achieved, even if the total number of turnovers is quite limited. In Jacobsen s complex 6a, particularly the bulky /-butyl substituents at positions 3 and 5 of the aromatic ring are crucial in directing the reactant and obtaining high ee values (86). 

There are two new examples of the use of chiral sulphinyl groups for induction of optical activity, in one case during the reduction of an imine to an amine with UAIH4 and in the other case during the alkylation of an aldehyde before cycliza-tion to an epoxide.In the latter case the reaction has been used as part of a sequence leading to the insect pheromone disparlure. N-Tosylsulphilimines (76) are converted in good yield and with high stereoselectivity into rrans-disubstituted oxirans (77) on reaction with NaH and an aromatic aldehyde. 

In further optimizations, Beller and coworkers examined various benzyl amines as replacement for pyrrolidine in the FeCl3-H2pydic catalyst system. They found thatthe use of different benzyl amines resulted in higher yields and better selectivity for the formation of epoxides, predominantly from aliphatic alkenes [111]. As seen in Table 2.8, the epoxidation of trans-l,2-disubstituted alkenes such as frans-2-octene and fruns-5-decene resulted in high yields, whereas aliphatic terminal alkenes appear to be problematic substrates. The epoxidation of aromatic alkenes using this catalytic system gave similar results to those obtained using pyrrolidine as base. 

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