Epoxides precursors

Epoxy-clay nanocomposites from epoxide precursors have been investigated by research groups at Michigan State University [34-40], Cornell University [41], and Case Western Reserve University [42,43]. In general, the synthesis is similar to that of Nylon-6 and PS... 

Several recent articles describe the ring-opening of chiral epoxides under microwave irradiation conditions (see also Scheme 6.103). In the context of the preparation of novel /32-adrenoceptor agonists related to formoterol and salmeterol, Fairhurst and a team from Novartis have described the synthesis of chiral ethanolamines by solvent-free microwave-assisted ring-opening of a suitable chiral epoxide precursor with secondary benzylated amines (Scheme 6.129) [262]. At 110 °C, the reaction occurred... 

Kim et al. (1) prepared the energetic agent poly(glycidyl dinitropropyl formal), (VI), by polymerizing the epoxide precursor, (VII), as illustrated in Eq. (2). The preparation of reaction intermediates is discussed by the authors (2). 

Since the introduction of the titanocene chloride dimer 67a to radical chemistry, much attention has been paid to render these reactions catalytic. This field was reviewed especially thoroughly for epoxides as substrates [123, 124, 142-145] so only catalyzed reactions using non-epoxide precursors and a few very recent examples of titanium-catalyzed epoxide-based cyclization reactions, which illustrate the principle, will be discussed here. A very useful feature of these reactions is that their rate constants were determined very recently [146], The reductive catalytic radical generation using 67a is not limited to epoxides. Oxetanes can also act as suitable precursors as demonstrated by pinacol couplings and reductive dimerizations [147]. Moreover, 5 mol% of 67a can serve as a catalyst for the 1,4-reduction of a, p-un saturated carbonyl compounds to ketones using zinc in the presence of triethylamine hydrochloride to regenerate the catalyst [148]. 

Concise theoretical studies of Ziegler145,146 analyzed all of the possible reaction pathways including the crossover from the singlet to the triplet surface with the transition state on the singlet surface while the formed product is a triplet species. It could be shown that the epoxide precursor is formed via a [3 + 2]-addition of ethylene to two Cr=0 bonds followed by rearrangement to the epoxide product (Scheme 10). 

The kaurene synthetase from Echinocystsis macrocarpa (wild cucumber) seed is able to cyclize both R- and 5-enantiomers of 14,15-oxidogeranylgeranyl pyrophosphate to give 3a- and 3/3-hydroxykaurene respectively in good yields. The degree of flexibility of substrate revealed by the diterpenoid cyclase makes more plausible previous proposals that naturally occurring axially hydroxylated terpenoids might arise by direct cyclization of appropriate epoxide precursors. 

Toxicology LD50 (oral, rat) > 5000 mg/kg nonirritating to skin nonmutagenic Uses Chain extender for elastomeric PU curing agent for PU elastomers, epoxides precursor for polyimides intermediate for org. synthesis... 

The postulated epoxide intermediates in the biosynthesis of the above-described lipid mediators is generally difficult to confirm experimentally due to synthetic challenges and the labile nature of these epoxides that are very readily hydrolyzed. Despite these difficulties, the involvement of the 13S,14S epoxide precursor in the biosynthesis of MaRl (Figure 9.7) was recently demonstrated [22], Stereochemically pure 13S,14S epoxide, prepared via stereocontrolled total synthesis, upon incubation... 

The biogenetic-type synthesis of a number of naturally occurring penta-cyclic triterpenoids and steroids from acyclic olefinic epoxide precursors has been achieved. Thus the epoxide (501) is transformed into dl-d-amynn (502) (8%) by SnCl4-MeN02 at 0 °C. ... 

How much of the biosynthetic operation can one expect to simulate in the organic laboratory The first studies directed toward nonenzymatic bio-genetic-like polyene cyclization were not promising. However, van Tamelen found that if the D-ring is preformed, the isoeuphenol system can be obtained in good yield by treatment of the epoxide precursor with a Lewis acid (207). 

Fig. 5.23. Van Tamelen s synthesis of the epoxide precursor of isoeuphenol system (207).

Scheme 3.24 Optical active a-sulfinyl epoxides precursors of chiral functionalized homoallylic alcohols.

The conformational analysis of certain 1,2-anhydrohexopyranose derivatives, and the synthesis of branched-chain sugars from epoxide precursors are covered in Chapters 20 and 13 respectively. 

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