Ring opening in epoxides

The course of the ring opening in epoxides derived from various exocyclic methylene compounds by treatment with lithium aluminum deuteride has been studied in the norbornane series. ... 

Acceleration of cure rates was reported by Crivello et al., when simultaneous photo initiated eationic polymerizations of epoxides and vinyl ethers are carried out in the presence of diaryliodonium salts. This, however, results in accelerations of ring-openings in epoxide polymerizations but deceleration of vinyl ether polymerizations. The effects are seen both, in mixtures of the two monofunetional monomers as well as in hybrid monomers that bear both functional groups simultaneously, vinyl ether and epirane groups... 

There is significant interest in controlling the absolute stereochemistry of ring opening in epoxide/C02 copolymerization. Cyciohexene oxide, a meso molecule, is an ideal substrate for desymmetrization using chiral catalysts. In 1999, Nozaki et al7 reported that a 1 1 mixture of ZnEt2 and (S)-diphenyl (pyrrolidine-2-yl)methanol (11) (Scheme 13) was active for stereoselective cyciohexene oxide/C02 copolymerization at 40 °C and 30 atm. CO2 (Scheme 14). The resultant polycarbonate contained 100% carbonate linkages, had an Ain of... 

We saw an example of nucleophilic ring opening of epoxides in Section 15 4 where the reaction of Grignard reagents with ethylene oxide was described as a synthetic route to primary alcohols... 

Acid-catalyzed ring opening of epoxides is discussed in Section 16.13. 

Reductive ring opening of epoxides in radical reactions in presence of titanocenes as electron transfer catalysts 98SL801. 

The 2,3-epoxy alcohols are often obtained in high optical purity (90% enantiomeric excess or higher), and are useful intermediates for further transformations. For example by nucleophilic ring opening the epoxide unit may be converted into an alcohol, a /3-hydroxy ether or a vicinal diol. 

Scheme 12.15 gives some examples of both acid-catalyzed and nucleophilic ring openings of epoxides. Entries 1 and 2 are cases in which epoxidation and solvolysis are carried out without isolation of the epoxide. Both cases also illustrate the preference for anti stereochemistry. The regioselectivity in Entry 3 is indicative of dominant bond cleavage in the TS. The reaction in Entry 4 was studied in a number of solvents. The product results from net syn addition as a result of phenonium ion participation. The ds-epoxide also gives mainly the syn product, presumably via isomerization to the... 

Metal oxides were also chirally modified and few of them showed a significant or at least useful e.s. Thus, while Al203/alkaloid [80] showed no enantiodifferentiation, Zn, Cu, and Cd tartrate salts were quite selective for a carbene addition (45% e.e.) [81] and for the nucleophilic ring opening of epoxides (up to 85% e.e.) [82], Recently, it was claimed that /(-zeolite, partially enriched in the chiral polymorph A, catalyzed the ring opening of an epoxide with low but significant e.s. (5% e.e.) [83], All these catalysts are notyet practically important but rather demonstrate that amorphous metal oxides can be modified successfully. 

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