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翻訳的超分子チオオートエステル化学

  • 0Department of Organic Chemistry, University of Geneva, Geneva, Switzerland.
Angewandte Chemie (International ed. in English) +

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2025年9月6日

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Preparation and Reactions of Thiols 02:33

6.7K

Thiols are prepared using the hydrosulfide anion as a nucleophile in a nucleophilic substitution reaction with alkyl halides. For instance, bromobutane reacts with sodium hydrosulfide to give butanethiol.

This reaction fails because the thiol product can undergo a second nucleophilic substitution reaction in the presence of an excess alkyl halide to generate a sulfide as a by-product.

This limitation can be overcome by using thiourea as the nucleophile. The reaction first produces an alkyl...

Thermal Electrocyclic Reactions: Stereochemistry 01:17

2.1K

The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Esters to β-Ketoesters: Claisen Condensation Mechanism 01:08

3.8K

Regular Claisen condensation involves the synthesis of β-ketoesters by combining identical ester molecules bearing two α hydrogens in the presence of an alkoxide base. The reaction commences with the deprotonation of the acidic α hydrogen by the base to form a resonance stabilized ester enolate. This nucleophilic ion then attacks the carbonyl center of another ester molecule to generate a tetrahedral alkoxide intermediate. Next, the expulsion of the alkoxide group from the...

Preparation of Epoxides 03:00

8.1K

Overview
Epoxides result from alkene oxidation, which can be achieved by a) air, b) peroxy acids, c) hypochlorous acids, and d) halohydrin cyclization.
Epoxidation with Peroxy Acids
Epoxidation of alkenes via oxidation with peroxy acids involves the conversion of a carbon–carbon double bond to an epoxide using the oxidizing agent meta-chloroperoxybenzoic acid, commonly known as MCPBA. Since the O–O bond of peroxy acids is very weak, the addition of electrophilic oxygen of...

Synthesis of α-Substituted Carbonyl Compounds: The Stork Enamine Reaction 01:26

3.5K

α-Substituted ketones or aldehydes can be synthesized from enamines by the Stork enamine reaction, named after its pioneer Gilbert Stork. Enamines are useful synthetic intermediates where the lone pair on nitrogen is in conjugation with the C=C bond. They resemble enolate ions, as the resonance forms of both species have a nucleophilic α carbon.

However, enamines are neutral and less reactive than enolates, which bear a net negative charge. Consequently, enamines are effective Michael donors...

Stereochemical Effects of Enolization 01:12

2.2K

The chiral α-carbon of the carbonyl compound is the stereocenter of the molecule. As shown in the figure below, when such a carbonyl compound undergoes racemization under an acidic or basic condition, an achiral enol is formed.

Under an acidic medium, an oxygen atom of the carbonyl group is protonated with simultaneous removal of the α-hydrogen, giving an enol.
Alternatively, in the basic medium, the removal of α-hydrogen generates a resonance-stabilized enolate. Next, the...