Dehydrative Cyclization Catalyzed by the Combination of Molybdenum(VI) Oxides and Benzoic Acids: First Synthesis of the Antitumour Substance BE‐70016

Abstract

AbstractThe dehydrative cyclization of N‐(o‐hydroxybenzoyl)threonine derivative 1a is efficiently promoted by the combined use of molybdenum(VI) oxides and benzoic acids bearing electron‐withdrawing substituents. In the presence of ammonium molybdate [(NH4)2MoO4, 10 mol %] and pentafluorobenzoic acid (C6F5CO2H; 10 mol %), dehydrative cyclization of 1a was conducted in toluene under azeotropic reflux conditions to give 2‐(o‐hydroxyphenyl)oxazoline 2a in 76 % yield. Furthermore, the first total synthesis of the antitumour substance BE‐70016 was achieved using the catalytic dehydrative cyclization of 1a as a key reaction.