Epoxidation organocatalysis

One of the early examples for organocatalysis is the asymmetric Weitz-Scheffer epoxidation of electron-deficient olefins, which can be effected either by organic chiral phase transfer catalysts (PTC) under biphasic conditions or by polyamino acids. This reaction has gained considerable attention and is of great synthetic use. 

Michael-aldol reaction as an alternative to the Morita-Baylis-Hillman reaction 14 recent results in conjugate addition of nitroalkanes to electron-poor alkenes 15 asymmetric cyclopropanation of chiral (l-phosphoryl)vinyl sulfoxides 16 synthetic methodology using tertiary phosphines as nucleophilic catalysts in combination with allenoates or 2-alkynoates 17 recent advances in the transition metal-catalysed asymmetric hydrosilylation of ketones, imines, and electrophilic C=C bonds 18 Michael additions catalysed by transition metals and lanthanide species 19 recent progress in asymmetric organocatalysis, including the aldol reaction, Mannich reaction, Michael addition, cycloadditions, allylation, epoxidation, and phase-transfer catalysis 20 and nucleophilic phosphine organocatalysis.21... 

This class of catalysts covers chemocatalysts that do not contain a transition metal. The class has been known for many years, but it is relatively recently that the term organocatalyst has been used (209). A wide variety of transformations can be performed, which is currently an area of intense research (209-218). Table 5 (220-252) summarizes some key transformations in which organocatalysis can be useful. Reactions range from the asymmetric epoxidation of alkenes, which need not be conjugated to another functional group, to aldol reactions and... 

P. C. B. Page, D. Barros, B. R. Buckley, A. Ardakani, B. A. Marples, Organocatalysis of asymmetric epoxidation mediated by iminium salts under nonaqueous conditions, /. Org. Chem. 69 (2004) 3595. 

Key Words Iminium, Oxaziridinium, Oxaziridine, Ketiminium, Oxone, Tetra-phenylphosphonium monoperoxysulphate, Isopinocampheylamine, Alkene, Epoxide, Enantiomeric excess. Asymmetric synthesis, Organocatalysis, 2-(2-Bromoethyl)benzaldehyde, Levcromakalim, Dihydroisoquinolinium, Spiro, Azepinium, Benzopyran, Dielectric constant, Binol. 2008 Elsevier B.v. 

P.C.B. Page, G. A. Rassias, D. Barros, A. Ardakani, D. Bethell, E. Merifield, New organocatalysis for the asymmetric catalytic epoxidation of alkenes mediated by chiral iminium salts, Synlett 4 (2002) 580. 

For an overview of the Julia-Colonna epoxidation of enones, see Berkessel, A. Groger, H. Asymmetric Organocatalysis , Wiley-VCH Weinheim, 2005, Chapter 10.2. 

Some other very important events in the historic development of asymmetric organocatalysis appeared between 1980 and the late 1990s, such as the development of the enantioselective alkylation of enolates using cinchona-alkaloid-based quaternary ammonium salts under phase-transfer conditions or the use of chiral Bronsted acids by Inoue or Jacobsen for the asymmetric hydro-cyanation of aldehydes and imines respectively. These initial reports acted as the launching point for a very rich chemistry that was extensively developed in the following years, such as the enantioselective catalysis by H-bonding activation or the asymmetric phase-transfer catalysis. The same would apply to the development of enantioselective versions of the Morita-Baylis-Hillman reaction,to the use of polyamino acids for the epoxidation of enones, also known as the Julia epoxidation or to the chemistry by Denmark in the phosphor-amide-catalyzed aldol reaction. ... 

Catalytic ring expansion ofthiiranes, aziridines, and oxiranes 13SL787. Organocatalysis in synthesis and reactions of epoxides and aziridines 13RCA11385. 

Another important highlight in organocatalysis was also developed in the 1980s. Julia and Colonna reported the epoxidation of enones by H2O2 catalyzed by poly-L-leucine. This example is formally the first use of hydrogen-bonding catalysis in asymmetric synthesis (Scheme 1.7) [19]. 

This chapter describes the chemical Hterature of aziridines and epoxides for the year 2013. As in previous years, this account does not provide a complete list of all uses and syntheses of aziridines and epoxides. Instead, the aim of this report is to provide an overview of synthetically valuable and intriguing methods that pertain to the reactions and synthesis of three-membered heterocycles. In particular, it should be noted that a review discussing organocatalysis in the synthesis and reactions of epoxides and aziridines was reported during the past year (13MI11385). 

The versatility of asymmetric organocatalysis was demonstrated by the practical synthesis of methyl (27, 35)-3-(4-methoxyphenyl)glycidate, a key intermediate in the synthesis of diltiazem. Therefore, the key step of this synthesis was the asymmetric epoxidation of methyl ( )-4-methoxyeiimamate using a chiral dioxirane generated from Yang s catalyst. This reaction provided the desired epoxide in high chemical and optical yields, as shown in Scheme 7.8. 

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