Unsaturated terminal epoxide

Scheme 8.28 Base-promoted intramolecular cyclopropanation of unsaturated terminal epoxides.

A hindered Hthium amide such as lithium 2,2,6,6-tetramethylpiperidide (LTMP) has proved to be effective in triggering a direct intramolecular cyclopropanation of the unsaturated terminal epoxide 31 to the tricycHc alcohol 32 (2010JOC2157). This strategy has been used successfully in a concise synthesis of (—)-cubelol (33) from (—)-menthone. Similarly, the naturally occurring (—)-10-epicubelol (34) can be prepared from (+)-menthone. Interestingly, whatever is the stereochemistry of the tethered alkene, the facial selectivity of cyclopropanation is controlled solely by the epoxide stereochemistry (Scheme 8). 

Hodgson and coworkers extended this concept to epoxides of unsaturated cyclic ethers 128 [5] and amines 130 [46, 47] (Scheme 5.28). It is interesting that the use of trimethylsilylmethyllithium as the organolithium in this case resulted in substituted allylsilanes 129 and 131 (R = CH2SiMe3) presumably the epoxide ring protons of 128 and 130 are more acidic than those of a simple terminal epoxide (see Scheme 5.26). 

Isomerization has been observed with many a,j3-unsaturated carboxylic acids such as w-cinnamic 10), angelic, maleic, and itaconic acids (94). The possibility of catalyzing the interconversion of, for example, 2-ethyl-butadiene and 3-methylpenta-l,3-diene has not apparently been explored. The cobalt cyanide hydride will also catalyze the isomerization of epoxides to ketones (even terminal epoxides give ketones, not aldehydes) as well as their reduction to alcohols. Since the yield of ketone increases with pH, it was suggested that reduction involved reaction with the hydride [Co" (CN)jH] and isomerization reaction with [Co (CN)j] 103). A related reaction is the decomposition of 2-bromoethanol to acetaldehyde... 

Sulfonyl carbanions are even more stable than sulfinyl carbanions and are consequently of greater significance in synthesis. They can be alkylated and acylated at the a-carbon atom using organolithium bases, and cyclic sulfones can be formed by intramolecular alkylation, (see Chapter 10, p. 202). Sulfonyl carbanions (73) also react with terminal epoxides, and this reaction is applicable for the synthesis of unsaturated alcohols (74) (Scheme 33). 

Sequences 1,2, and 3 of Scheme 3.25, to yield unsaturated epoxy alcohols. In Sequence 1, the terminal epoxide was isolated prior to conversion to trans 5S)-55. Sequence 2 of Scheme 3.25 illustrates the complete unraveling of the C-glycoside to yield a conjugated diene diol as a reaction competing with the formation of the desired epoxy alcohol. The formation of compounds such as the diene diol formed the basis for one of the syntheses of LTB4 described earlier in Scheme... 

The fruit oil of the leguminous tree Pterodon pubescens contains geranylgeraniol (3) and its terminal epoxide (98). This terminal epoxide is highly lethal to the cercariae of Schistosoma mansoni, the causative agent of schistosomiasis (Gilbert, 1977). Other unsaturated diterpenes such as dehy-droabietic acid, agathic acid, and copalic acid prevent cercar-ial penetration. 

The vinyl esters are derived from epoxy resins, adducts of bis-phenol A and epichlorhydrin, by reaction of the terminal epoxide groups with methacrylic acid (Structure 9.2) [11, 12]. Thus, these resins have only terminal unsaturation, but do... 

Although hydrogenation of A-benzylideneaniline in the presence of 11 afforded the corresponding product (eq. 1 in Scheme 11), the a,(3-unsaturated ketone was converted into a mixture of unsaturated and saturated alcohols in the 42 56 ratio (eq. 2 in Scheme 11). Several substrates (nitrile derivatives, epoxides, esters, internal alkynes, and terminal alkenes), which are shown in Fig. 4, are not hydrogenated in this catalytic system. 

Asymmetric epoxidation of a,jS-unsaturated ketones represents an efficient method for the preparation of optically active a,jS-epoxy ketonesJ Recently, a new and very efficient catalytic system for enantioselective epoxidation of ( )-a,jS-enones to the corresponding trans-epoxy ketones has been developed based on a BlNOL-zinc complexJ Very high yields and excellent diastereo- and enantioselectivities are achieved at room temperature using cumene hydroperoxide (CMHP) as the terminal oxidant and performing the reaction in diethyl ether. A combination of enantio-merically pure BINOL and diethylzinc readily affords the active catalyst in situ (Figure 6.13). ... 

The selective epoxidation of dienes by CPO from C. jumago has been reported (Scheme 2.23) [275]. The methacrylate was a good substrate which showed two types of selectivity only the isolated double bond was epoxidized to produce the monoepoxide in 73% yield and the conjugated a, 3-unsaturated bond of the methacrylic acid moiety was untouched. It was suggested that conjugated terminal alkenes might... 

Epoxidized oils such as soybean oil or linseed oil, which are made by oxidizing the internal unsaturation in the fatty acid chain, find much use as plasticizers, particularly in vinyl resins. An internal epoxy ring is much less reactive than a terminal epoxy ring and usually does not take part in typical epoxy curing reactions under mild conditions. These materials can be used as plasticizers in epoxy adhesives but cannot really be considered reactive diluents. 

The nature of the Lewis acid and the residence time in the reactor drastically affect the ratio exo/endo of these terminal unsaturations. AICI3-based initiation leads to about 10% of vinylidenes with respect to total unsaturations, whereas the use of BF3-based catalysts, allowing a shorter contact time between the acid and the polymer and thus limiting isomerization, increases this exo structure to 70% or more [25,29]. The vinylidene double bond is much more reactive than the endo one, and favors considerably the furt her terminal functionalization of the oligomers for example, maleination, epoxidation, ozonolysis, reaction with phosphorus pentasul-fide, etc. (Fig. 2). 

Several epoxides hearing multiply-bonded substituents have lice ll subjected to alcohol addition. Treatment of several vinyl-sulistitutwl ethylene oxides with sodium methoxide, for example, has been reportid to yield alcohols eorrasponding to attack on the epoxide carbon iLloni furthest from the unsaturated function. - . > In the presence of a trace of mineral acid, however, methanol adds to the oppcmiic terminal of tbo epoxide ring (Eq- 666),... 

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