Epoxides ring opening reactions with nucleophile

The PS-TBD catalyst has been shown to be effective for epoxide ring opening reactions with several nucleophiles such as thiols under solvent free conditions [37,78] (Scheme 6.21). In this case, the reusabihty of the catalyst was also established without a significant loss of reactivity and selectivity. As a related work, the utility of mesoporous silica-supported TBD catalysts was demonstrated in the reaction of propylene oxide with carbon dioxide to prepare the corresponding carbonate derivative under the ultrasonic activation [79]. 

There are limited data on 1,2-epoxy of glycal epoxide ring opening reaction with C-nucleophiles other than organocuprate, e.g., Grignard reagents [217, 218], organolithium compounds [217-219], aUylstannane [217], and sodio di-tert-butyl malonate [219, 220]. 

Functional groups were selectively introduced at the C-2 position of isophorone by epoxide ring-opening by several nucleophiles with active methylene groups. Different behavior was observed depending on the reaction conditions and the nature of the nucleophilic agents [57]. The best experimental systems involved PTC or KF-alumina under solvent-free conditions and MW irradiation (Eq. 37 and Tab. 5.15). 

Asymmetric microbial oxidation afforded the (-)-epoxide which has been explored as a building block ring opening reactions with organometallic nucleophiles, and via Friedel-Crafts reactions have been reported. [226,227]. A non-biotransformative approach to this epoxide has also been described [228]. Copper(II)-catalysed oxidative hydrolysis (Eq. 72) affords a lactic acid analogue in high enantiomeric purity [229]. 

Like epoxides, aziridines engage in facile ring-opening reactions with a variety of nucleophiles, and this represents an entry into many functionalized amines. For example, the 3-trifluoromethylaziridine-2-carboxyIatc 159 undergoes efficient nucleophilic attack by chloride or thiols under acidic conditions to provide the protected amino esters 160 and 161, respectively, in high yield and as a single diastcreomer <01SL679>. 

Alkyllithiums react quite differently with cyclic sulfides compared to the normal nucleophilic ring-opening reaction with epoxides (35,36). Ethyllithium reacts with 2-methylthiacyclopropane to generate propylene and lithium ethanethiolate. The resulting lithium ethanethiolate is capable of initiating polymerization of 2-methylthiacyclopropane. 

Ethers are not normally susceptible to reaction with nucleophiles. Epoxides, however, are different. Because of the strain associated with a three-membered ring, epoxides undergo ring-opening reactions with a variety of nucleophiles. Good nucleophiles... 

In the previous section, v e sav f the reactions of epoxides with strong nucleophiles. The driving force for such reactions was the removal of ring strain associated with the three-membered ring of an epoxide. Ring-opening reactions can also occur under acidic conditions. As an example, consider the reaction between ethylene oxide and HX. 

There is an important difference in the regiochemistry of ring opening reactions of epoxides depending on the reaction conditions Unsymmetncally substituted epoxides tend to react with anionic nucleophiles at the less hindered carbon of the ring Under conditions of acid catalysis however the more highly substituted carbon is attacked... 

Primary cycloaUphatic amines react with phosgene to form isocyanates. Reaction of isocyanates with primary and secondary amines forms ureas. Dehydration of ureas or dehydrosulfuri2ation of thioureas results in carhodiimides. The nucleophilicity that deterrnines rapid amine reactivity with acid chlorides and isocyanates also promotes epoxide ring opening to form hydroxyalkyl- and dihydroxyalkylaniines. Michael addition to acrylonitrile yields stable cyanoethylcycloalkylarnines. 

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