Boronic acid/Brønsted acid co-catalyst systems for the synthesis of 2H-chromenes from phenols and α, β-unsaturated carbonyls. Issue 28 (17th June 2016)

• Record Type: Journal Article
• Authors: Dimakos, Victoria; Singh, Tishaan; Taylor, Mark S.
• Is Part Of: Organic & biomolecular chemistry. Volume 14:Issue 28(2016)
• Page Start: 6703
• Page End: 6711
• Publication Date: 2016-06-17
• Subjects: Chemistry, Organic -- Periodicals; Bioorganic chemistry -- Periodicals; Chemistry, Physical organic -- Periodicals; 547
• DOI: 10.1039/c6ob01026a
• Languages: English
• ISSNs: 1477-0520

Abstract

Abstract : Combinations of boronic acids and Brønsted acids showing optimal co-catalytic activity for condensations of enals or enones with phenols have been identified, enabling an efficient synthesis of 2 H -chromenes. Abstract : Protocols for the synthesis of substituted 2 H -chromenes from α, β-unsaturated carbonyls and phenols are described. Optimal combinations of arylboronic acids and Brønsted acids have been identified, such that both can be employed in catalytic quantities to accelerate these condensations. The method has been used to synthesize a variety of substituted 2 H -chromenes, as well as photochromic naphthopyrans. The use of pentafluorophenylboronic acid and diphenylphosphinic acid enabled an expansion of the electrophile scope to include α, β-unsaturated ketones. Hall's 'phase-switching' of boronic acids has been exploited to achieve the separation of the two co-catalysts from unpurified reaction mixtures by a simple liquid–liquid extraction.