Highly efficient intramolecular general acid catalysis of enol ether hydrolysis, with rapid proton transfer to carbon

1994 ◽  
pp. 649 ◽  
Author(s):  
Anthony J. Kirby ◽  
Fiona O'Carroll
Keyword(s):  
Proton Transfer ◽  
Acid Catalysis ◽  
Enol Ether ◽  
Highly Efficient ◽  
Rapid Proton ◽  
General Acid

A mechanism for efficient proton-transfer catalysis. Intramolecular general acid catalysis of the hydrolysis of 1-arylethyl ethers of salicylic acid

1999 ◽  
Vol 77 (5-6) ◽  
pp. 792-801 ◽  
Author(s):  
Sarah E Barber ◽  
Kathryn ES Dean ◽  
Anthony J Kirby
Keyword(s):  
Hydrogen Bond ◽  
Salicylic Acid ◽  
Proton Transfer ◽  
Acid Catalysis ◽  
Enzyme Mechanism ◽  
Base Catalysis ◽  
Strong Hydrogen Bond ◽  
Cooh Group ◽  
Tert Butyl ◽  
General Acid

The tert-butyl (1) and 1-arylethyl ethers (2) of salicylic acid are hydrolyzed with efficient general acid catalysis by the ortho-COOH group. The half-life of the neutral COOH form of the tert-butyl ether is 15.2 min at 39°, and the estimated acceleration by the COOH group of 2, X = Me, Y = H is 2.13 × 105. The salicylate leaving group from 2 (X = Me, Y = H) has an effective pKa of 2.9, compared with a nominal pKa of 8.52. Analysis of substituent effects in both arylethyl and leaving groups provides the most detailed available mechanistic insight into a reaction involving efficient intramolecular proton-transfer catalysis. The mechanism is very different from classical general acid-base catalysis. Proton transfer takes place very rapidly within a developing strong hydrogen bond, and though an integral part of the C—O cleavage process is practically uncoupled from it. "Strategic delay" of the proton-transfer step, relative to C—O cleavage, makes a significant contribution to efficiency by setting up the conditions for the formation of the strong, intramolecular hydrogen bond.Key words: catalysis, carboxyl, hydrogen bond, proton transfer, enzyme mechanism.

Reactions of aryldiazonium salts and alkyl arylazo ethers. VIII. General acid catalysis of the ionization of alkyl (E)-arylazo ethers in alcoholic solvents

1982 ◽  
Vol 35 (5) ◽  
pp. 961 ◽  
Author(s):  
TJ Broxton ◽  
AC Stray
Keyword(s):  
Ionic Strength ◽  
Proton Transfer ◽  
Aromatic Ring ◽  
Acid Catalysis ◽  
Bond Breaking ◽  
General Acid

Further studies of the general acid-catalysed ionization of alkyl (E)-arylazo ethers in alcoholic solvents have been carried out. The magnitude of catalysis and the degree of proton transfer as a function of the substituent on the aromatic ring, the alkoxide ion nucleofuge, the solvent and the ionic strength have been studied. The results are consistent with a mechanism for the acid-catalysed ionization of alkyl (E)-arylazo ethers in which proton transfer and N-O bond breaking are concerted. 1H and 13C n.m.r. data for a number of alkyl p-nitrophenylazo ethers are reported.

Intramolecular Diels–Alder Reactions of Oxazoles, Imidazoles, and Thiazoles

Synthesis ◽  
2020 ◽  
Author(s):  
Peter Wipf ◽  
Thanh T. Nguyen
Keyword(s):  
Natural Products ◽  
Lewis Acid ◽  
Acid Catalysis ◽  
Copper Catalysts ◽  
Diels Alder ◽  
Synthetic Approach ◽  
Highly Efficient ◽  
Intramolecular Cycloadditions ◽  
Western Segment ◽  
Target Molecules

AbstractThe development of the intramolecular Diels–Alder cycloaddition­ of azole heterocycles, i.e. oxazoles (IMDAO), imidazoles (IMDAI), and thiazoles (IMDAT), has had a significant impact on the efficient preparation of heterocyclic intermediates and natural products. In particular, highly efficient and versatile IMDAO reactions have been utilized as a key step in several synthetic schemes to provide alkaloids and terpenoid target molecules. More limited studies have been performed on IMDAI and IMDAT cycloadditions. Some drawbacks, such as the occasionally­ challenging preparation of IMDA precursors, are also highlighted in this review. Perspectives are provided on how IMDAI and IMDAT­ transformations can be further expanded for target-directed syntheses.1 Introduction2 Oxazoles2.1 IMDAO Approaches to Furanosesquiterpenes and Furanosteroids2.1.1 Syntheses of Highly Oxygenated Sesquiterpenes2.1.2 Syntheses of (±)-Gnididione and (±)-Isognididione2.1.3 Synthesis of (±)-Stemoamide2.1.4 Synthesis of (±)-Paniculide A2.1.5 Syntheses of (+)- and (–)-Norsecurinine2.1.6 Synthesis of Evodone2.1.7 Syntheses of (±)-Ligularone and (±)-Petasalbine2.1.8 Syntheses of Imerubrine, Isoimerubrine, and Grandirubrine2.1.9 Syntheses of Furanosteroids2.1.10 Syntheses of Substituted Indolines and Tetrahydroquinolines2.2 IMDAO Approaches to Pyridines: the Kondrat’eva Reaction2.2.1 Syntheses of Suaveoline and Norsuaveoline2.2.2 Synthesis of Eupolauramine2.2.3 Syntheses of (–)-Plectrodorine and (+)-Oxerine2.2.4 Synthesis of Amphimedine2.2.5 Synthetic Approach to the Western Segment of Haplophytine2.2.6 Synthesis of Marinoquinoline A2.2.6.1 IMDAO Approach to Marinoquinoline A2.2.6.2 Scope of Allenyl IMDAO Cycloaddition2.3 Lewis Acid Catalysis in IMDAO Reactions2.3.1 Effects of Europium Catalysts on IMDAO Reactions2.3.2 Effects of Copper Catalysts on IMDAO Reactions3 Imidazoles 4 Thiazoles4.1 Syntheses of Menthane and Eremophilane4.2 Further Comments on the Intramolecular Cycloadditions of Thiocarbonyl Ylides5 Conclusions and Outlook

Sign in / Sign up

Export Citation Format

Share Document