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37.2.3 Synthesis by Carbonyl Epoxidation

DOI: 10.1055/sos-SD-037-00188

Aggarwal, V. K.; Crimmin, M.; Riches, S.Science of Synthesis, (200837321.

General Introduction

Epoxides have found long-standing applications in organic synthesis due to their propensity to undergo highly regio- and stereoselective ring-opening reactions.[‌1‌,‌2‌] These strained three-membered heterocyclic ethers are typically aerobically and thermally stable compounds, which may be isolated by standard synthetic chemistry techniques. Exceptions to this, however, include particularly strained epoxides, or those that are functionalized by electron-donating substituents, which can render them unstable under acidic, basic, or thermal conditions.[‌3‌] 1,2-Disubstituted, 1,2,2-trisubstituted, and 1,1,2,2-tetrasubstituted epoxides may potentially exist as a mixture of trans- and cis-diastereomers due to the two contiguous stereocenters of the heterocyclic ring. Often the stereoisomers may be differentiated by chromatographic techniques and separated by preparative chromatography. Importantly for 1,2-disubstituted epoxides, the trans- and cis-diastereomers may be distinguished by 1H NMR spectroscopy, with 3J1H1H coupling constants taking typical values of approximately 3 and 4.5Hz for trans- and cis-epoxides, respectively.[‌4‌] Similarly, nuclear Overhauser effect (nOe) techniques may be used to differentiate the diastereomers of 1,2,2-trisubstituted and 1,1,2,2-tetrasubstituted epoxides.

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References