Organic Synthesis International: Oxidant- and hydrogen acceptor-free palladium catalyzed dehydrogenative cyclization of acylhydrazones to substituted oxadiazoles

Oxidant- and hydrogen acceptor-free palladium catalyzed dehydrogenative cyclization of acylhydrazones to substituted oxadiazoles

Org. Chem. Front., 2018, Advance Article
DOI: 10.1039/C7QO00749C, Research Article

Qiangqiang Jiang, Xinghui Qi, Chenyang Zhang, Xuan Ji, Jin Li, Renhua Liu

Oxidant- and hydrogen acceptor-free palladium catalyzed dehydrogenative cyclization of acylhydrazones to substituted oxadiazoles

Qiangqiang Jiang,a Xinghui Qi,a Chenyang Zhang,a Xuan Ji,a Jin Li*b and Renhua Liu*a

*Corresponding authors

aSchool of Pharmacy, East China University of Science and Technology, Meilong Road 130, Shanghai 200237, China
E-mail: liurh@ecust.edu.cn

bChina Catalyst Holding Co., Ltd, Jingjiu Road 3, Chemical Park, Songmu Island, Puwan New District, Dalian 116699, China
E-mail: lijin@china-catalyst.com

Abstract

An efficient method for the synthesis of 2,5-disubstituted 1,3,4-oxadiazoles has been developed through palladium(0) catalyzed dehydrogenative cyclization of N-arylidenearoylhydrazides. By using this method, a wide range of functionalized and potentially biologically relevant 1,3,4-oxadiazole-containing compounds have been accessed in moderate to high isolated yields. The dehydrogenative cyclization process is characterized by the nonuse of any sacrificing hydrogen acceptors or oxidants and hydrogen gas as the only by-product, and therefore circumvents the recurring problems of over-oxidation and the compatibility with easily oxidizable functionalities in oxidation protocols.

109.6 mg, 87 % yield; White solid,

1H NMR (400 MHz, CDCl3) δ 8.13 – 8.08 (m, 2H), 8.06 (d, J = 8.7 Hz, 2H), 7.52 (m, 3H), 7.01 (d, J = 8.7 Hz, 2H), 3.86 (s, 3H);

13C NMR (100 MHz, CDCl3) δ 164.51, 164.10, 162.33, 131.54, 129.03, 128.67, 126.80, 124.05, 116.38, 114.50, 55.46; M.p. 145-146 oC.

2-(4-methoxyphenyl)-5-phenyl-1,3,4-oxadiazole