Some series of 2-alkyl (alkythio)-5-((4-chloro)-3-ethyl-1-methyl-1H-pyrazole-5-yl)-1,3, 4-oxadiazoles (thiadiazoles) were prepared as potential fungicides. Their fungicidal activity was evaluated against rice sheath blight, which is a major disease of rice in China. Structure-activity relationships for the screened compounds were evaluated and discussed. It was found that 5-(4-chloro-3-ethyl-1-methyl-1H-pyrazole-5-yl)-1,3, 4-thiadiazole-2-thione has the higher fungicidal activity.

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Keywords 5( . % b & & p~-5 ' -y l ) -l , 3 , Cthiadiazole,zol-5'-yl)-1,3,4--oxadiamle, fungicidal activity, PGR activity -(~u b s t ; h a c d -~y r S E o l -' -~) -1 , 2 , C~e , 5-(substiMdpyra- ReceivedNovember 12, 1999; m p t e d February 22, 2000. ROj& ( No. 29832050) suppcxtd by the National Natural Science Foundation of China. VoI. 18 No. 4 Zoo0Chinese Jd af chemistry 597 (85 % ) to form 4-amino-5-( ~ubstit~ted pyrtlzol-5-yl) -1, produced quantitatively. when crmpound 3 ~t e d with 2,4-triiezole-3-thimes 9, followed by akyhtion giving compounds 10. The treatment of 8a with concentrated HZW4 yielded 5-( substituted pyrazol-5-yl)-1,3,4-thiadiazole-2-thione 11. When 3 was oocidized by hydrogen peroxide in ethanol, the mmqondjng disultide l2 was 1,3-dibmmopmpane using a phase transfer catdyst tetrabutylammonium bromide (TBAB) , a mixture of 1,3-bis (5-( s u b s t i t u t e d~l -5 -y l ) -l ,3,4-thiadiaz01-2-~1thio)-prOpane 14 and 2-( 3-bmmwl)thio-5-( substituted pyraz01-5-~1)-1 3,4-thiadiazole I3 was obtained (scheme 2).

A New Method for the Synthesis of Thieno[2,3-c]pyrazoles -[based on the consecutive reaction of pyrazoleacetates of type (VI) with CS 2 and MeI].