Epoxidation table

The Aggarwal group has used chiral sulfide 7, derived from camphorsulfonyl chloride, in asymmetric epoxidation [4]. Firstly, they prefonned the salt 8 from either the bromide or the alcohol, and then formed the ylide in the presence of a range of carbonyl compounds. This process proved effective for the synthesis of aryl-aryl, aryl-heteroaryl, aryl-alkyl, and aryl-vinyl epoxides (Table 1.2, Entries 1-5). 

Since Eisch and Galle first introduced organyl substituents as anion-stabilizing groups for lithiated epoxides (Table 5.4, Entries 8-9) they have examined them extensively (Table 5.5) [54, 65]. 

The principle cost determinant in typical hydrolytic or phenolic resolutions is the cobalt catalyst, despite the relatively low catalyst loadings used in most cases and the demonstrated recyclability with key substrates. From this standpoint, recently developed oligomeric (salen)Co complexes, discussed earlier in this chapter in the context of the hydrolytic desymmetrization of meso-epoxides (Scheme 7.16), offer significant advantages for kinetic resolutions of racemic terminal epoxides (Table 7.3) [29-31]. For the hydrolytic and phenolic kinetic resolutions, the oligo-... 

There are several examples of successful dienol epoxidations (Table 9.2). Catalytic SAE conditions are generally better than stoichiometric for reactive substrates (Entry 1), whilst stoichiometric conditions, on the other hand, are useful for less reactive substrates. Small variations in substrate structure can cause large differences in reactivity and product stability pentadienol could be epoxidized in acceptable yield, whereas hexadienol gave a complex mixture of products (Entries 1, 2). 

An allenyllithium intermediate was implicated in the reaction of BuLi with an alkynylated cyclohexene epoxide (Table 9.5) [11], It was found that addition of 2equiv. of BuLi to the alkynyloxirane in the presence of 5mol% CuBr-2PPh3 led, after quenching with H20, not to the expected SN2 butylated allene, but instead to the protonolysis product. Likewise, quenching the reaction with Mel or MeSSMe led to the methylated and thiolated allenes, respectively. Furthermore, the putative lithioallene could be trapped by C02 or PhCHO to yield the expected adducts. 

Annis et al. [69] reported the synthesis of polystyrene- 36 and silica bound Co(salen) 37 and their use in HKR of racemic epoxides (Scheme 7-9). Polystyrene bound systems 36 demonstrated highly practical solutions to certain technical difficulties associated with the isolation of reaction products from HKR especially problematic substrates like epichlorohydrin and other high boiling epoxides (Table 1). 

Tomioka and coworkers reported ketones 15 and 16 as asymmetric epoxidation catalysts (Fig. 5) [42,43]. Ketone 15 was found to be prone to Baeyer-Vilhger oxidation to the lactone, thus giving low yield for the epoxidation (Table 1, entry 14). Epoxidation results were much improved with tricychc ketone 16 (Table 1, entries 15, 24). 

Chiral Ketone and Iminium Catalysts for Olefin Epoxidation Table 3 Asymmetric epoxidation with ketone 26... 

Primary allylic alcohols can be successfully resolved by the Sharpless epoxidation (Table 14), which may be performed in the stoichiometric or the catalytic modification with similar success. 

Many hundreds of affinity labels have been synthesized, the majority based on halomethyl ketones or epoxides (Table 9.3). They are listed each year in the Specialist Periodical Reports Amino-Acids, Peptides, and Proteins, published by the Royal Society of Chemistry (U.K.). 

Asymmetric Methods of Epoxidation Table 6 Epoxides from (2,3 )>Disubstituted Allylic Alcohols... 

Dimethylallyl aloteol was epoxidized with >90% ee (Table 7, entry 1) but in low yield when a stoichiometric amount of tee titanium tartrate conqtlex was used. However, when a catalytic amount of tee complex was used and in situ derivatization employed, tee p-nitrobenzoate (>98% ee after recrystalli-zation) and p-toluenesulfonate (93% ee) were isolated in yields of 70% and 55%, respectively. Likewise, tee epoxidation of geraniol with a stoichiometric amount of tee conqtlex gave the epoxide (Table 7, entry 3) in 77% yield (95% ee) which was improved to 95% yield (91% ee) when a catalytic amount of complex was used (entry 4). 

The monooxygenation of methylstyrene (PhCH=CHMe) to form the epoxide (Table 9) appears to involve an O-atom transfer from the end-on configuration (13) of the Fe (ROOH) + complex (eqnation 83). 

Whereas peracids do not exhibit any face discriminating steric effect in the epoxidation of (S)-limoncne (Table 2, entries 3 and 4), due to the shallow topography of the molecule in the half-chair conformation (in accord with an MM2 simulation168), oxaziridine-mediated and molybdenum-catalyzed epoxidations (Table 2, entries 5 and 7 versus entries 1 and 2) show appreciable, but opposite, diastereoselectivity. 

Surprisingly, JV-methylation of the alanyl group in one of these alkenes has been reported to retain the very high syn selectivity of peracid epoxidation (Table 9, entries 10 and 11) from the stereochemical outcome of these two epoxidations it has been argued that a second NH hydrogen... 

Another modified metal hydride, lithium triethylborohydride, the so-called superhydride , has been introduced as a powerful reducing agent especially suitable for trisubstituted, tetrasubstituted and bicy-clic epoxides (Table 3). With trisubstituted epoxides the regiochemistry is completely controlled to give only tertiary alcohols. No skeletal rearrangement is observed for benzonorbomadiene oxide. 

Zeolite in the present reaction [Eq. (7)] is assumed to work not only as a support that finely disperses NaNj, but also as an acid catalyst to facilitate the cleavage of the C—O bond of the epoxide. Table VIII summarizes the relationship between maximum acid strength of the zeolite support and ring opening of 1,2-epoxyoctane with the supported NaNa. Both the combined yield of 7a and 7b and the ratio of 7a to 7b were closely related to the acid properties of the zeolite used. As the acid strength of the zeolite increased, an increase in the yield and a decrease in the ratio were observed. 

Enantioselective oxidation of olefins is a very elegant way of introducing oxygen and in some cases also nitrogen functions into molecules. The catalytic methods with the highest industrial potential are epoxidation and dihydroxylation, and the kinetic resolution of racemic terminal epoxides (Table 3). 

Actually the aerobic oxidation of acetaldehyde in acetonitrile solution at RT and atmospheric pressure in oxygen in the presence of alkenes and catalytic amounts of NHPI led to the corresponding epoxides (Table 6.3). No oxidation occurred under the same conditions in the absence of NHPI, clearly indicating that Eq. (6.12) plays a key role in the aerobic epoxidation. 

The best epoxidation results thus far were reported by Beller and coworkers using an in situ generated epoxidation catalyst capable of up to 100% conversion of a range of aryl olefins to epoxides (Table 18.2) [44]. They used a combination of... 

The supported reagent is capable of catalysing oxidation reactions including the oxidation of alkylaromatics using air as the oxidant, and the selective oxidation of alkenes to epoxides (Table 1) in the presence of air and an aldehyde. 

An intriguing inversion of oxygen configuration occurs in the formation of minor products from the 4)5,5)5-epoxide and the 3)5-hydroxy-5a,6a-epoxide (Table 4) (cf also p. 373). A mechanism which satisfactorily explains inversion consists of rupture and re-closure of the ring carrying the oxygen substituent. Scheme 21 illustrates this mechanism for the 4/5,5)5-epoxide (577). The essential... 

Trisubstituted Epoxides. To date, only a limited set of data are available on the enzymatic hydrolysis of trisubstituted epoxides (Table 11.2-7). Regardless of their steric bulkiness, however, they seem to be accepted by epoxide hydrolases from bacterial1110, 119], fungal[92, 941 and yeast[9S1 sources, as long as the access to one side of the substrate is not too severely restricted (e.g. a 2,2-dimethyl-3-alkyloxirane). Further data are required to depict a general selectivity pattern within this group of substrates. 

R1 and R2 samples were analyzed under the following conditions a) as grafted b) as grafted but without H2( in the grafting procedure c) same as a) but activated as reported in TABLE 1. run d d) same as c) but after the usual cyclohexene epoxidation. TABLE 2 reports also the observed binding energies relative to three samples chosen as standards, namely the inorganic precursor used (Na MoO ) and... 

Production of 102 during the lime was lower with ihe supponed caialysi MCM-4I-TBD than ihal obtained in the reaction perfonned w iih ihe homogeneous catalyst MTBD. suggesting that the suppiirted catalyst suffers from some dilTusion resistance. The synthetic process has been applied to different epoxides (Table 13). 

The reaction has been studied intensively, and earlier results including the mechanistic aspects of the reaction as well as the fundamental properties of the copolymer were reviewedThe most effective catalyst systems for this copolymerization so far examined are those based on organozinc and related compounds ). The catalyst systems so far reported, from several groups, for the copolymerization of carbon dioxide and epoxide (mainly propylene oxide) are summarized in Table 1. Diethylzinc-water system is applicable to the copolymerization of carbon dioxide and various epoxides (Table 2). 

Animals that have the digestive organ known as the liver appear to utilize the liver monooxygenases to convert benzene (CeU.) and other arenes to epoxides (Table 6.10, item 2) on the way to phenols (Table 6.10, item 2) and quinones (Table 6.10, item 4) that might then be excreted or further oxidized (ultimately to carbon... 

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