Aluminum Triflate Catalyzed Tandem Reactions of d-Galactal: Toward Chiral Benzopyrans, Chromenes, and Chromans

Abstract

3,4,6-Tri-O-acetyl-D-galactal is selectively converted into 1-O-aryl-2-deoxy derivatives or chiral bridged benzopyrans under Al(OTf)3 catalysis, depending on reaction conditions. The benzopyrans react with Al(OTf)3/acetic anhydride in ring-opening reactions in the absence or presence of acetic acid to selectively produce chiral chromenes or chromans, respectively, in high yields.

Scope and advances in the catalytic propargylic substitution reaction

“…Importantly, it tolerates protic conditions and so can be readily recycled by simply extracting it in water and recovered by subsequent removal of the water. 52 A water-tolerant reusable Al(OTf) 3 Lewis acid catalyst for the propargylation of indoles 61 in reuxing acetonitrile was reported by Bezuidenhoudt and co-workers in the year 2012, Scheme 24. 53 From the environmental point of view, water-tolerant Lewis acids are quite attractive due to their recyclability and reusability attributes and the by-product from the reaction is also non-hazardous H 2 O.…”

Protecting group-free use of alcohols as carbon electrophiles in atom efficient aluminium triflate-catalysed dehydrative nucleophilic displacement reactions

“…Signicant efforts have been made towards the synthesis of the 2H-chromene motif, 22 including sugar-derived chiral systems. 23 In addition, there has Scheme 2 Conversion of benzyl ethers into C-alkylated products. been continuing interest in heteroatom analogues of chromenes such as dihydroquinolines 24 and thiochromenes, 25 which are also associated with biological activity.…”

Aluminum triflate catalyzed Povarov reaction for the synthesis of pyranotetrahydroquinolines

“…Williams and Cullen reported that Al(OTf) 3 was an effective recyclable catalyst (<10 mol% catalyst loading) for the ring opening of epoxides with amines to provide β-amino alcohols without the catalyst being deactivated by the nucleophile amine or hydroxyl amine product. 36 Inspired by this result and in continuation of our research into the application of Al(OTf) 3 in a number of catalytic transformations such as in the synthesis of chiral O-heterocycles, 37 tetrahydropyranyl and tetrahydrofuranyl protection/deprotection of alcohols 38 and temperature-switched selective Oglycosylation, 39 we have evaluated its catalytic activity in the three component Povarov reaction and herein report its scope and limitations.…”