Synthesis and Chemistry of Agrochemicals V - American Chemical

Chapter 28

Arylazo- and Arylazoxy-Oximes as Fungicides

Downloaded by STANFORD UNIV GREEN LIBR on June 18, 2012 | http://pubs.acs.org Publication Date: May 14, 1998 | doi: 10.1021/bk-1998-0686.ch028

WilliamW.Wood, Andrew C. G. Gray, and ThomasW.Naisby Cyanamid Agricultural Research Center, American Cyanamid Corporation, P.O. Box 400, Princeton,ΝJ08543-0400

A number of azo- and azoxy-oximes have been synthesized and tested as potential agricultural fungicides. Several of these compounds showed impressive levels of activity, particularly against Plasmopara viticola and Erisyphe graminis. The most active compounds were those with ap-chlorineor p-methyl substituent on the aryl ring.

Arylazo- and arylazoxy-oximes have been known for many years, but have not been reported to show any useful biological function. The majority of literature references to these compounds deal with their coordination properties. One patent application has recently appeared in which the azoxime function appears as an adjunct to a strobilurin-type fungicide (7). As part of an extensive fungicide programme in the area, we have studied the fungicidal properties of azo- and azoxy-derivatives and report a summary of this work herein. For the purposes of this study, azo- and azoxy-derivatives may be divided into four structural types according to the substitution at the Cterminus and oxidation level of the azo-double bond (Figure 1). Thus Class 1 azo- and Class 2 azoxy-compounds carry only a proton on the C-terminus, while Class 3 and Class 4 represent analogues which have alkyl or aryl groups attached to the oxime-bearing carbon. Synthesis Several different synthesis protocols were adopted or adapted from the literature to prepare the compounds detailed in this study. Class 1 azooximes could be prepared by addition of dipotassium malonate to an aryl diazonium salt as detailed in Scheme 1 (2). No intermediates were isolated in this procedure, but rather the malonate adduct was acidified with acetic acid and diazotized to form the nitroso moiety. Two successive decarboxylations then lead to a nitroso product, one of the tautomeric forms of the target. As detailed in Table I, a number of compounds were prepared by this route, but yields were generally very poor, irrespective of the substitution pattern on the aryl ring. Extensive chromatography was also required to

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©1998 American Chemical Society

In Synthesis and Chemistry of Agrochemicals V; Baker, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1998.

285


N-terminus

NOH

C-terminus

0

NOH

Θ

Class 2

Class 1

0

NOH

NOH

Θ

Λ»

Class 3

Λ

Class 4

Figure 1: Structural Types of Azoxime

Scheme 1: Diazonium Route to Azo-oximes H C(C0 K) 2

2

2

+

ArN +

HO

2

A r

/N^ ^CH(C0 K) N

2

2

NaNO , HOAc, z

(-co) 2

-CO, Ar

/ N

" ^ N. " A ", C 0 K 2

^OH

J


286 obtain samples of adequate purity. In the light of these problems, other synthetic approaches were investigated. Table I: Examples of the Synthesis of Class 1 Azo-oximes by the Diazonium Route


R 4-C1 4-Me 4-OEt 4-Br 4-fBu 2-OMe 4-OMe 4-CONH

2

Yield (%) v(4) 9 8.9 3.7

o®

Compounds (5) and (6), representing Classes 1 and 3, were also among the most active compounds tested at the lower dose rates (Table XIII). Both of these compounds gave good control of Eg even at the lowest dose rate of 30 ppm. They were, however, clearly differentiated against Pv where the


294 unsubstituted compound (5) broke between 100 and 30 ppm, while the Cphenyl derivative (6) broke sharply at 100 ppm.


Table XIII: Class 1 vs Class 3 Activity Dose (ppm) 300 100 ~W Eg (5) 8.8 7.1 6.8 Eg(6) 8.8 6.5 6.9 />v(5) 9 8.9 5.1 Pv(6) 9 6.8 0.2

H

Ph

Conclusion A number of azo- and azoxy- oximes have been synthesized and tested as potential agricultural fungicides. Several of these compounds showed impressive levels of activity, particularly against Plasmopara viticola and Erisyphe graminis. The most active compounds were those with a p-chlorine or /7-methyl substituent on the aryl ring. Literature Cited 1. 2. 3. 4. 5. 6.

Ziegler,H;Trah, S WO 9316986 (to Ciba-Geigy). Shawali,A.S.;Altahou, B.M. Tetrahedron, 1977, 33(13), 1625. Bamberger,E.;Pemsel,W.;Chem.Ber., 1903, 36, 85. Kalia,K.C.;Chakravorty,Α.;J.Org.Chem., 1970, 35(7), 2231. Armand, J.; Furth, B; Kossanyi, J.; Morizur,J.P.;Bull.Soc.Chim.Fr., 1968, (6), 2499. Hunter,L.;Roberts,C.B.;J.Chem.Soc., 1941, 823.


Synthesis and Chemistry of Agrochemicals V - American Chemical

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