Selective Catalytic Hydration of Alkynes in the Presence of Au‐Cavitands: A Study in Structure–Activity Relationships

• Published in: European journal of organic chemistry 2018-10, Vol.2018 (38), p.5304-5311
• Main Authors: Inoue, Mami, Ugawa, Katto, Maruyama, Tomoyuki, Iwasawa, Tetsuo
• Format: Article
• Language: English
• Subjects: Alkynes; Aromatic compounds; Bifunctional cavitands; Catalysis; Catalytic activity; Cavitands; Gold; Holes; Hydration; Methylene; Regioselectivity; Structure–activity relationships; Supramolecular catalysis; Supramolecular chemistry
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.201800948

The effects of the catalytic cavities in gold‐functionalized cavitands in the hydration of internal alkynes have been studied. Variations on cavitand structures revealed the importance of two features that were studied: (1) flanking aromatic rings, and (2) an adjacent P=O moiety. The di‐quinoxaline‐spanned resorcin[4]arene system provides a well‐defined compartment, in which a cationic Au ion activates an internal alkyne for conversion into a ketone by delivery of water that has also been activated, this time by a P=O moiety. We synthesized four variations on our parent cavitand. Variations of the cavitand walls include replacement of quinoxaline components with pyrazine or methylene units. Variation of the P=O center was accomplished with methylene or quinoxaline moieties. All variants displayed lower catalytic activity or selectivity, allowing us to confirm the significance both of an internal cavity and of an activation site for water. Supramolecular catalysis was investigated by comparative studies with corresponding model catalysts featuring weakened cage architecture and functionality. A diquinoxaline‐spanned resorcin[4]arene bearing Lewis acid and base components selectively catalyzed alkyne hydration, allowing us to investigate structure–activity relationships and to identify significant skeletons.