Hafnium Triflate as an Efficient Catalyst for Direct Friedel–Crafts Reactions of Chromene Hemiacetals

Abstract

Abstract:The direct Friedel-Crafts reaction of chromene hemiacetals with indoles, furans and sterically hindered anilines has been accomplished with high selectivity and excellent yields in the presence of a catalytic amount of hafnium triflate [HfA C H T U N G T R E N N U N G (OTf) 4 , 0.1 mol%, 0-40 8C]. The mild conditions tolerate various sensitive functional and protecting groups, and the products were confirmed unambiguously from their spectra and by single-crystal X-ray analysis. This direct Friedel-Crafts reaction of chromene hemiacetals should inspire and encourage the consideration of hafnium triflate in the development of mild reaction conditions for the efficient derivatization of hemiacetal-containing compounds.

Direct Sulfination of Nonactivated Alcohols with Arylsulfonylmethyl Isocyanides

“…Recently, Xiong and co‐workers reported a BF 3 · OEt 2 ‐promoted direct substitution of alcohols with sodium sulfinates (180 mol‐% of BF 3 · OEt 2 , 50 °C). [7e] In connection with our consistent interest in direct substitution of activated hydroxy groups,[7d], herein we would like to report a direct sulfination of nonactivated hydroxy groups with arylsulfonylmethyl isocyanides under mild conditions [10 mol‐% of Bi(OTf) 3 , 25 °C]…”

A Highly Efficient Friedel–Crafts Reaction of 3‐Hydroxyoxindoles and Aromatic Compounds to 3,3‐Diaryl and 3‐Alkyl‐3‐aryloxindoles Catalyzed by Hg(ClO4)2⋅3 H2O

“…The catalytic Friedel-Crafts reaction [6] of 3-hydroxyoxindoles 2 and aromatic compounds would be an atom-efficient Abstract: We report a highly efficient Friedel-Crafts reaction of 3-alkyl or 3aryl 3-hydroxyoxindoles with a variety of aromatic and heteroaromatic compounds to unsymmetrical 3,3-diaryloxindoles or 3-alkyl-3-aryloxindoles, which are interesting medicinal targets and useful building blocks for the synthesis of natural products. Hg-A C H T U N G T R E N N U N G (ClO 4 ) 2 ·3 H 2 O was identified as a pow-erful catalyst for this reaction, and is significantly more efficient than other screened metal perchlorate hydrates and Brønsted acids such as HOTf and HClO 4 .…”

Synthetic Studies on Potent Marine Drugs: Synthesis and the Crystal Structure of 6‐tert‐butyl‐4‐phenyl‐4H‐chromene‐2‐carboxylic Acid

“…During our ongoing interest aiming at the synthesis of functional heterocycles [31][32][33][34], we have developed several synthetic strategies for the preparation various 2H-chromenes [35][36][37][38]. In one case, we isolated a trace of 6-tert-butyl-4-phenyl-4H-chromene-2-carboxylate methyl ester (13a) whose structure has been determined by single-crystal X-ray analysis.…”