319
the oxirane ring further onto the acid framework. That is, acids serve as temporary
reservoir of electronic charge during the reaction to maintain high nucleophilicity
of oxirane and to reduce overlap repulsion between the substrate and the attacking
nucleophile.
10.5 Conclusion
In this brief review, there are summarized the results of quantum chemical investigation of epoxides transformation in neutral, alkaline and acidic environment. It has
been shown that in the presence of both basic and acid catalysts back-side attack of
nucleophile is more preferable if compared to front-side approach due to strong repulsion between nucleophile and oxygen atom of epoxide. Having the same stereochemistry the reactions in alkaline and acid medium possess opposite regiochemisty—protonation facilitates nucleophile attack on the less substituted carbon atom
resulted in formation of abnormal product while in alkaline medium nucleophile
forms bond with more substituted carbon atom. Uncatalyzed transformation of epoxides is characterized by high values of activation energy. Modeling hydrolysis
of oxirane with explicit consideration of one and two water molecules showed the
preference of front-side attack. For neutral aminolysis, on the other hand, backside attack is more favorite where four-water cluster assists the proton transfer,
and strengthens both the entering and the leaving groups through a charge-transfer
process induced by different strengths between the two proton-transfer processes.
Detailed analysis of epoxides model reactions in different environment
built background for theoretical modeling of large-scaled biologically valuable
processes.
References
1. Yudin AK (2006) Aziridines and epoxides in organic synthesis. Wiley, Weinheim
2. Stirling CJM (1985) Evaluation of the effect of strain upon reactivity. Tetrahedron 41(9):1613–
1666
3. Bartok M, Lang KL (1980) The chemistry of functional groups. Supplement E. In: Patai S (ed)
The chemistry of ethers, hydroxyl groups and their sulfur analogues. Part 2. Willey, New York,
pp 609–682
4. Lewars EG (1984) Structure of small and large rings. In: Katritzky AR, Rees CW, Lwowski W
(eds) Comprehensive heterocyclic chemistry, vol 7. Pergamon, New York, pp 95–130
5. Dittmer DC (1984) Thiiranes and Thiirenes. In: Katritzky AR, Rees CW, Lwowski W (eds)
Comprehensive heterocyclic chemistry, vol 7. Pergamon, New York, pp 131–184
6. Crandall JK, Lin L-HC (1968) Base-promoted reactions of epoxides. V. 1-Alkylcycloalkene
oxides. J Org Chem 33(6):2375–2378
7. Gronert S, Lee JM (1995) Gas phase reactions of methyloxirane with HO − and methylthiirane
with HO
−
and HS
−
. An ab initio study of addition and elimination. J Org Chem 60(14):4488–
4497
10 Quantum-Chemical Investigation of Epoxidic Compounds Transformation
the oxirane ring further onto the acid framework. That is, acids serve as temporary
reservoir of electronic charge during the reaction to maintain high nucleophilicity
of oxirane and to reduce overlap repulsion between the substrate and the attacking
nucleophile.
10.5 Conclusion
In this brief review, there are summarized the results of quantum chemical investigation of epoxides transformation in neutral, alkaline and acidic environment. It has
been shown that in the presence of both basic and acid catalysts back-side attack of
nucleophile is more preferable if compared to front-side approach due to strong repulsion between nucleophile and oxygen atom of epoxide. Having the same stereochemistry the reactions in alkaline and acid medium possess opposite regiochemisty—protonation facilitates nucleophile attack on the less substituted carbon atom
resulted in formation of abnormal product while in alkaline medium nucleophile
forms bond with more substituted carbon atom. Uncatalyzed transformation of epoxides is characterized by high values of activation energy. Modeling hydrolysis
of oxirane with explicit consideration of one and two water molecules showed the
preference of front-side attack. For neutral aminolysis, on the other hand, backside attack is more favorite where four-water cluster assists the proton transfer,
and strengthens both the entering and the leaving groups through a charge-transfer
process induced by different strengths between the two proton-transfer processes.
Detailed analysis of epoxides model reactions in different environment
built background for theoretical modeling of large-scaled biologically valuable
processes.
References
1. Yudin AK (2006) Aziridines and epoxides in organic synthesis. Wiley, Weinheim
2. Stirling CJM (1985) Evaluation of the effect of strain upon reactivity. Tetrahedron 41(9):1613–
1666
3. Bartok M, Lang KL (1980) The chemistry of functional groups. Supplement E. In: Patai S (ed)
The chemistry of ethers, hydroxyl groups and their sulfur analogues. Part 2. Willey, New York,
pp 609–682
4. Lewars EG (1984) Structure of small and large rings. In: Katritzky AR, Rees CW, Lwowski W
(eds) Comprehensive heterocyclic chemistry, vol 7. Pergamon, New York, pp 95–130
5. Dittmer DC (1984) Thiiranes and Thiirenes. In: Katritzky AR, Rees CW, Lwowski W (eds)
Comprehensive heterocyclic chemistry, vol 7. Pergamon, New York, pp 131–184
6. Crandall JK, Lin L-HC (1968) Base-promoted reactions of epoxides. V. 1-Alkylcycloalkene
oxides. J Org Chem 33(6):2375–2378
7. Gronert S, Lee JM (1995) Gas phase reactions of methyloxirane with HO − and methylthiirane
with HO
−
and HS
−
. An ab initio study of addition and elimination. J Org Chem 60(14):4488–
4497
10 Quantum-Chemical Investigation of Epoxidic Compounds Transformation