Palladium-catalyzed Cycloaddition of Aryl Silylethynyl Ethers with Isocyanates via<i>o</i>-C–H Cleavage
作者:Yasunori Minami、Mayuko Kanda、Tamejiro Hiyama
DOI:10.1246/cl.140452
日期:2014.9.5
Palladium-catalyzed cycloaddition of alkynyl aryl ethers with isocyanates proceeds through o-C–H activation to afford 2-methylidene-2H-1,4-benzoxazin-3(4H)-one derivatives. Deuterium-labeling experiment shows that o-hydrogen is cleaved selectively and migrated to 2-methylidene moiety in the product. Various substrates are applied to this transformation to afford various substituted cycloadducts. 1,4-Bis(alkynoxy)benzenes can be used for the synthesis of multicondensed cycles to afford benzo[1,2-b:4,5-b′]bis[1,4]oxazine-3,8-dione derivatives.
Palladium-catalyzed annulation of alkynyl aryl ethers with isocyanates through o-C–H cleavage. Synthesis of solid-state emissive 2-methylidene-2H-1,4-benzoxazin-3(4H)-ones
The title transformation can be achieved by the o-C-H cleavage of allcynyl aryl ethers, which is easily derived from phenols, followed by the insertion/annulation with isocyanates in the presence of a palladium catalyst. Various alkynyl aryl ethers and arylisocyanates are applied to this transformation to give the corresponding cyclic products. Mechanistic study indicates that the C-H cleavage is effected reversibly by the concerted metalation-deprotonation pathway. The products exhibit solid-state luminescence upon irradiation of UV light. Fluorescent maxima and quantum yields can be controlled by the substituents at appropriate sites in the products. (C) 2015 Elsevier Ltd. All rights reserved.