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Chapter 14. Epoxides

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1. Nomenclature

2. Reactions

3. Synthesis Methods

1. Nomenclature

⑴ Oxa Type

① Named as cycloalkane at the end

② Oxygen forming the ring is labeled as 1

③ The carbon with the most substituents is labeled as 2, and if the numbers are the same, alphabetical order is followed

⑵ Oxirane Type

① Named as oxirane at the end

② Oxygen forming the ring is labeled as 1

③ The carbon with the most substituents is labeled as 2, and if the numbers are the same, alphabetical order is followed

④ Example: 2-methyl-3-phenyloxirane

Figure 1. 2-methyl-3-phenyloxirane

⑶ Epoxyalkane Type

① Terminal carbon is labeled as 1

② If connected to the 3rd and 4th carbons, named as 3,4-epoxy-

③ Substituents are named in alphabetical order after the numbers are determined

⑷ Alkene Oxide Type

① Terminal carbon of the alkene is numbered to have the lower number

② Substituents are named in alphabetical order after the numbers are determined

2. Reactions

⑴ Overview

① Ring-opening reactions

② Epoxides are more reactive than ethers due to ring strain

⑵ Acid-Catalyzed Ring-Opening Reaction: Proceeds similar to S_N1 reaction

① Mechanism

Figure 2. Acid-Catalyzed Epoxide Ring-Opening Reaction

② (Formula) Can be understood as an S_N1-like reaction where initially, oxygen captures a proton, creating a carbocation on the carbon with more substitution

⑶ Base-Catalyzed Ring-Opening Reaction: Proceeds similar to S_N2 reaction

① Mechanism

Figure 3. Base-Catalyzed Epoxide Ring-Opening Reaction

② (Formula) Strong nucleophile attacks, avoiding steric hindrance

⑷ Fürst-Plattner Rule

① For cyclic carbon compounds, the ring opens such that the -OH group and the nucleophile become trans axial.

② The ring opens in the axial direction of the chair form but not in the axial direction of the twist boat form.

③ Reason for trans axial conformation: Related to backside attack

⑸ Grignard Reagent Ring-Opening Reaction

① Mechanism

Figure 4. Grignard Reagent Ring-Opening Reaction

② (Formula) Strong nucleophile attacks, avoiding steric hindrance

3. Synthesis Methods

⑴ Alkene + Peroxycarboxylic Acid

⑵ Payne Epoxidation

⑶ Halohydrin Formation Reaction + Intramolecular S_N2 Reaction

Figure 5. Epoxide Synthesis through Halohydrin Pathway

⑷ Johnson-Corey-Chaykovsky Reaction

Input: 2020.03.04 00:57

Modified: 2022.02.02 01:54