Bifunctional epoxides

Avoid bifunctional or potentially bifunctional epoxides, especially when the epoxide groups are at the terminal end of an alkyl chain, as they are more reactive than epoxy groups interdispersed or attached to a rigid ring due to higher molecular flexibility to interact with DNA. 

PREPARATION OF VALUABLE CHIRAL BUILDING BLOCKS FOR THE SYNTHESIS OF BIOLOGICALLY ACTIVE COMPOUNDS STARTING FROM BIFUNCTIONAL EPOXIDES... 

The potential of such reaction sequences for the generation of molecular diversity was also demonstrated by the synthesis of a library of heterocycles. Epoxide ring-opening with hydrazine and subsequent condensation with (3-diketones or other bifunctional electrophiles gave rise to a variety of functionalized heterocyclic structures in high purity [34]. A selection based on the substrate derived from cyclohexene oxide is shown in Scheme 12.12. 

Gomez GA, Morisseau C, Hammock BD, Christianson DW. Structure of human epoxide hydrolase reveals mechanistic inferences on bifunctional catalysis in epoxide and phosphate ester hydrolysis. Biochemistry 2004 43 4716-23. 

It is worth mentioning that both the carboxylation of epoxides and anilines are acid-base reactions, which do not entail redox processes. Therefore a catalyst active in these reactions must provide acid-base functionality. In this perspective, positively charged gold could be the real player, although a co-catalytic or promotion effect of ze-rovalent gold could also be important. Therefore the catalysts for the oxidative carbonylation of aniline, supported on Merck Ion-exchanger IV, could be actually bifunctional. On one side, Au could catalyze the oxidation of CO with O2 to CO2, a reaction for which it is... 

Epoxides are extremely useful intermediates in organic synthesis since they react with a variety of nucleophiles suffering opening of the epoxide ring with retention or inversion of configuration at the carbon undergoing attack. Thus, the development of highly stereoselective methods for the synthesis of certain chiral epoxides, such as the methods under discussion, has enabled the asymmetric synthesis of a wide variety of 1,2-bifunctional compounds. 

Wu, M. H. Jacobsen, E. N. (1998) Asymmetric ring opening of meso-epoxides with thiols enantiomeric enrichment using a bifunctional nucleophile., J. Org. Chem., 63 5252-5254. 

Snapper and Hoveyda reported a catalytic enantioselective Strecker reaction of aldimines using peptide-based chiral titanium complex [Eq. (13.11)]. Rapid and combinatorial tuning of the catalyst structure is possible in their approach. Based on kinetic studies, bifunctional transition state model 24 was proposed, in which titanium acts as a Lewis acid to activate an imine and an amide carbonyl oxygen acts as a Bronsted base to deprotonate HCN. Related catalyst is also effective in an enantioselective epoxide opening by cyanide "... 

The Tsuji-Trost-type reaction is applicable to bifunctional vinyl epoxide 144 and 1,3-diketone using a palladium catalyst as demonstrated by Koizumi, who obtained polymer 145 (Equation (67)). The reaction proceeds at 0 °C to a reflux temperature of THE. The resulting polymer 145 is isolated in a quantitative yield. The molecular weight of 145 is ca. 3000 (PDI = 2.0-2.7) when 5 mol% of Pd(PPh3)4 is employed as a catalyst. Use of Pd2(dba)3 with several bidentate phosphines such as dppe, dppp, dppb, and dppf is also effective for the polymerization reaction. Propargyl carbonate 146 also reacts with bisphenols in the presence of a palladium catalyst to afford polyethers 147 via carbon-oxygen bond formation at s - and r/) -carbon atoms (Equation (68)). 

If bifunctional or potentially bifunctional (e.g., containing a double bond) epoxides are absolutely essential, separate the epoxides (or the epoxide and the double bond) by more than six carbon atoms. 

In contrast to the non-catalyzed reaction, the base-initiated copolymerization was found to be a specific reaction 35,36,39 -45) and the consumption of both monomers, epoxide and anhydride, is the same. The initiator not only affects the rate of copolymerization but also suppresses the undesirable homopolymerization of the epoxide. At equimolar ratio, epoxide and anhydride are strictly bifunctional. 

Another relatively simple system for the epoxidation of tri- and c/r-disubstituted olefins is formamide-hydrogen peroxide in an aqueous medium. This reagent has the advantage of being pH-independent, which makes it attractive for biochemically mediated transformations. No reaction was observed in the case of /ran.v-disubstituted and terminal olefins. With bifunctional alkenes, the more reactive double bond is selectively epoxidized [95TL4015]. 

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