Studies on Heteropentalenes. V. : Cycloadditions of 5-Aryl-3-methylimidazo[5,1-b]thiazoles with acetylenic Esters Leading to 5-Aryl-3-methyl-thiazolo[2,3-c]benzimidazoles and Related Heterocycles

Creators Abe Noritaka

Creators Nishiwaki Tarozaemon

Creators Ikeda Kotaro

Cycloaddition of 5-aryl-3-methylimidazo[5,1-b]thiazoles with dialkyl acetylenedicarboxylate in an aprotic nonpolar solvent gives a number of products including epimeric thiazolo[2,3-c]benzimidazoles (3 and 4) [1:2-cycloadducts], epimeric 5,10b-ethenothiazolo[3',2':3,4]imidazo[1,5-a]-pyridines (5 and 6) [1:3-cycloadducts], and thiazolo[3',2':3,4]imidazo[1,2-a]pyridines [1:3-adducts]. At higher temperature, formation of the 1:2-cycloadducts is favored over the 1:3-adducts, whereas the latter predominates at room temperature. In an aprotic polar medium, the 1:3-cycloadducts (5 and 6) and tetraalkyl 6-arylpyridine-2,3,4,5-tetracarboxylates are substantially produced. Epimerization of 3 and 4 has been found to compete well with fragmentation to 4H-1,4-benzothiazine.

[ISSN]0009-2673

[NCID]AA00580132

https://doi.org/10.1246/bcsj.55.2464

[isPartOf] [URI]http://www.jstage.jst.go.jp/browse/bcsj/-char/en