Synthesis and Chemistry of Agrochemicals III - American Chemical

Chapter 7

Novel N-Substituted Imidazolinones Synthesis and Herbicidal Activity

Downloaded by UNIV OF PITTSBURGH on October 14, 2015 | http://pubs.acs.org Publication Date: September 22, 1992 | doi: 10.1021/bk-1992-0504.ch007

M . A. Guaciaro, M . Los, D. L. Little, P. A. Marc, and L. Quakenbush Agricultural Research Division, American Cyanamid Company, P.O. Box 400, Princeton, NJ 08543-0400

In an effort to prepare new imidazolinone herbicides with the required combination of weed control, crop safety and reduced soil persistence, various novel N-hydroxy, N-chloro- and N-cyanoimidazolinones were synthesized. The N-hydroxyimidazolinones, although interesting from a synthetic standpoint, did not show a significant advantage over their imidazolinone counterparts in the greenhouse. The N-chloroimidazolinones showed better weed control and crop safety than their imidazolinone precursors in several instances but showed no evidence of reduced soil persistence. The N-cyanoimidazolinones exhibited excellent weed control and crop selectivity with evidence of reduced soil persistence, depending upon the nature of the carboxylate substituent.

Previous papers in the imidazolinone area have discussed the effects on herbicidal activity produced by changes in the aryl rings, the aryl ring substituents, the nature of the imidazolinone carbonyl and the alkyl substituents on the imidazolinone ring (1-22). In the area covered by this paper, it was reasoned that substitution of various functional groups, such as chloro, hydroxyl and cyano on the imidazolinone nitrogen might afford new herbicides with different weed control/crop safety spectra. In addition, it was reasoned that certain electron-withdrawing N-substituents, in particular cyano, might make the imidazolinone ring more susceptible to breakdown in the soil, thus reducing the soil persistence of the herbicide. A = CH, N F*! = H, alkyl R = H, alkyl, benzyl, furfuryl, allyl R = CI. OH, CN 2

o

3

0097-6156/92/0504-0056$06.00/0 © 1992 American Chemical Society In Synthesis and Chemistry of Agrochemicals III; Baker, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1992.

7. GUACIARO ET AL.

Novel ^-Substituted Imidazolinones

57

This paper will discuss the synthesis and herbicidal activity of various N-hydroxy-, N-chloro- and N-cyanoimidazolinones (25).


N-Hydroxyimidazolinones Synthesis. Since there was no existing method for the preparation of N-hydroxyimidazolinones of this type, we proposed the following synthesis. Oximes of type 3 can be prepared from the readily available aldehydes 2 (24). Chlorination of these oximes, using NCS (24, 25), chlorine (26) or f-butylhypochlorite (27) would afford chloro-oximes of type 4. We reasoned that the chloro-oximes 4, when treated with triethylamine in the presence of aminoester 6, would form intermediates of type 7 which could cyclize to either bezoxazinones 8 or oxadiazinones 9.

In Synthesis and Chemistry of Agrochemicals III; Baker, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1992.

58

SYNTHESIS AND CHEMISTRY OF AGROCHEMICALS HI


Oxadiazinones of type 11, with no ortho-carboxyl group, had been prepared previously in our labs (Los, M., American Cyanamid Co., Agricultural Research Division, unpublished data, 1976) using the nitrile oxide cycloaddition shown below (28). These oxadiazinones show characteristic carbonyl bands in their IR spectra at 1750 cm-1 and fragment in the mass spectrometer with loss of carbon dioxide.

We subsequently discovered that treatment of oxadiazinones of type 11 with sodium hydride in THF afforded N-hydroxyimidazolinones of type 14, presumably via the ring contraction mechanism shown below. This ring contraction may also be accomplished with sodium hydroxide. These N-hydroxyimidazolinones exhibit proton and carbon NMR spectra which are quite similar to NMR spectra of the imidazolinones with respect to the chemical shifts and coupling constants of the methyl and isopropyl protons and with respect to the chemical shifts of the imidazolinone ring carbonyl and ring carbons.

Therefore, if the cycloaddition of the nitrile oxide derived from chloro-oxime 4 with aminoester 6 afforded oxadiazinones of type 9, we reasoned that base treatment of these oxadiazinones would afford the target compounds of type 15. If, on the other hand, benzoxazinones of type 8 formed, then base treatment of them might also afford targets of type 15 via intermediates 16 and 17.



7. GUACIARO ET AL.


59

Toward this end, treatment of aldehyde 18 with hydroxylamine hydrochloride afforded oxime 19, which was chlorinated with NCS to afford 20 in high yield. Treatment of 20 with triethylamine in the presence of aminoester 6 afforded benzoxazinone 21, which was identified on the basis of its IR (NH: 3290 cm-1, carbonyls: 1725 and 1705 cm-1), proton NMR (loss of benzyl ester; retention of methyl ester singlet) and mass spectrum (loss of carbon dioxide).


60

SYNTHESIS AND CHEMISTRY OF AGROCHEMICALS i n

Treatment of 21 with excess sodium hydroxide at room temperature afforded one product. The product was identified as hydroxyimidazolinone 22 on the basis of its NMR, IR and mass spectral data. The structural assignment was confirmed by a single crystal X-ray analysis (Whittle, R. R., Oneida Research Services, New Hartford, NY, 1985, unpublished data).


COOH

22

In the imazapyr area, chlorination of oxime 23 afforded 24 in high yield. Treatment of chloro-oxime 24 with triethylamine and aminoester 6 afforded 25 in 58% yield. Hydroxyimidazolinone 26 was isolated from the reaction of 25 with sodium hydroxide in 50% yield after recrystallization.

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Biological Activity. Table I compares hydroxyimidazolinone 22 to its imidazolinone counterpart 27 preemergence at 500 g/ha. Compound 22 showed good overall grass control but was less effective than 27 in controlling morningglory and velvetleaf in the broadleaf area. Both compounds were toxic to crops. Table II compares hydroxyimidazolinone 26 to imazapyr 28 postemergence at 63 g/ha. Compound 26 was safer than imazapyr on crops with safety on sunflower and marginal safety on corn and soybeans. It was less effective than 28 in controlling broadleaves. Preemergence, 26 behaved as a total vegetation control agent down to 63 g/ha but was less effective than imazapyr in controlling broadleaves.


GUACIARO ET AL.


Table I. Comparison of hydroxyimidazolinone 22 to imidazolinone 27 at 500 g/ha preemergence


COOH

COOH

22

Compound 22 27

27 % Control Grasses Broadleaves 71 71

53 66

% Injury Crops 65 86

Table II. Comparison of hydroxyimidazolinone 26 to imazapyr 28 at 63 g/ha postemergence

% Injury or % Control Species Sunflower Soybean Corn Matricaria Velvetleaf Ragweed Morningglory Field Bindweed Foxtail Quackgrass Wild Oats Purple Nutsedge Barnyardgrass

26 0 22 22 0 67 0 55 0 100 33 78 0 100

28 100 93 100 81 96 71 96 100 100 98 100 86 94


62

SYNTHESIS AND CHEMISTRY OF AGROCHEMICALS III

N-Chloroimidazolinones


Synthesis. N-Chloroimidazolinones of type 29 were prepared by treating the appropriate imidazolinyl carboxylate with terf-butyl hypochlorite at room temperature with the exclusion of light.

Rl = H, alkyl R = alkyl 2

29

When chloroimidazolinone 30 was treated with dilute sodium hydroxide in an attempt to hydrolyze the methyl ester, cleavage of the nitrogen-chlorine bond also occurred, affording imazapyr 28 as the sole product. These results imply that the chloroimidazolinones might degrade in the plant or soil to their parent imidazolinones with no reduction in soil persistence.

30 Stable at pH 6-7

28

Herbicidal Activity. Chloroimidazolinone 30 behaved as a total vegetation control agent preemergence but was less effective than its parent imidazolinone. Table i n compares chloroimidazolinone 32 to imidazolinone 33 preemergence at 16 g/ha. Introduction of a chlorine onto the imidazolinone ring in this case affords a compound with better overall preemergence weed control. Compound 32 showed better control of velvetleaf, wild mustard, field bindweed, quackgrass, wild oats and purple nutsedge with improved safety on soybeans. N-Cyanoimidazolinones The rationale for placement of a cyano group on the imidazolinone nitrogen was not only to study the effect of this substitution on herbicidal activity, but also to determine whether the presence of an N-cyano group would make the imidazolinone ring more susceptible to ring opening and hence to detoxification.


GUACIARO ET AL.



Table III. Comparison of chloroimidazolinone 32 to imidazolinone 33 preemergence at 16 g/ha

32

R = CI

33

R=H

% Injury or % Control Species Soybeans Wheat Velvetleaf Ragweed Wild Mustard Morningglory Field Bindweed Quackgrass Wild Oats Purple Nutsedge Foxtail Barnyardgrass

32 6 22 89 0 100 55 100 100 89 89 78 11

33 19 3 73 4 89 44 70 26 67 72 72 16


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Figure 1 shows two potential degradation pathways for N-cyanoimidazolinones of type 34. Hydrolysis would produce acids of type 35, which could undergo nucleophilic attack at the imidazolinone C-2 position, affording intermediates of type 36. In Pathway A, cyclization of 36 to tricycles of type 37 followed by formation of imides of type 38 could be followed by imide ring opening and loss of cyanide to afford open chain compounds of type 40. Pathway B would afford 40 via ring opening of 36, tautomerization of 39 and loss of cyanide. Open chain compounds of type 40 are known to have minimal to no herbicidal activity. Such a process would therefore result in reduced soil persistence. Synthesis: Esters. Esters in this area can be prepared by treating the appropriate imidazolinone with sodium hydride followed by cyanogen bromide to afford the products shown below in yields ranging from 60 to 100%.

41 42 43 44 45

Ri Ri Ri Ri Ri

= = = = =

Me Et Et Me Me

R R R R R

2

2

2

2

2

= Me = p-methoxybenzyl = furfuryl = p-methoxybenzyl = allyl

Herbicidal Activity: Esters. Table IV compares cyanoimidazolinone 41 to its parent 33 postemergence at 63 g/ha. Both compounds were marginally safe on corn while 33 was slightly safer on wheat. Compound 41 was more effective in controlling morningglory and quackgrass while 33 was more effective in controlling field bindweed and much more effective in controlling purple nutsedge. Both compounds showed good control of velvetleaf, wild mustard, wild oats and foxtail. Table V compares cyanoimidazolinone 42 to imidazolinone 46 preemergence at 125 g/ha. Although 46 showed good to excellent control of broadleaves and grasses, it was also injurious to the crops. Cyanoimidazolinone 42, on the other hand, was totally safe on wheat and soybeans with 11% injury to corn and marginal safety on cotton. Compound 42 showed good control of velvetleaf, wild mustard, field bindweed, quackgrass, purple nutsedge, foxtail and barnyardgrass. Table VI compares the furfuryl esters 43 and 47 preemergence at 63 g/ha. Imidazolinone 47 was more effective in controlling ragweed, morningglory and wild oats but 43 was safer on wheat and soybeans with good overall grass control. At 125 g/ha postemergence (Table VII) imidazolinone 47 showed better control of wild oats, velvet leaf and ragweed but was more toxic to soybeans than 43. Cyanoimidazolinone 43 was completely safe on soybeans and controlled purple nutsedge more effectively than 47.


7.

GUACIAROETJU^


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SYNTHESIS AND CHEMISTRY OF AGROCHEMICALS HI

Table IV. Comparison of imidazolinone 33 to cyanoimidazolinone 41 postemergence at 63 g/ha

33

R=H

41

R = CN

% Injury or % Control Species

33

Corn Wheat Ragweed Velvetleaf Wild Mustard Morningglory Field Bindweed Quackgrass Wild Oats Foxtail Purple Nutsedge Barnyardgrass

22 7.0 25 80 80 44 83 17 98 92 58 55

41 22 11 22 78 89 67 67 44 89 89 0 67



GUACIARO ET AL.


Table V. Comparison of imidazolinone 46 to cyanbimidazolinone 42 at 125 g/ha preemergence

46

R=H

42

R = CN


46

42

Wheat Soybeans Cotton Corn Velvetleaf Ragweed Wild Mustard Morningglory Field Bindweed Quackgrass Wild Oats Purple Nutsedge Foxtail Barnyardgrass

67 17 78 78 89 89 100 78 100 100 100 100 100 100

0 0 22 11 89 0 100 55 89 100 44 78 78 78




Table VI. Comparison of cyanoimidazolinone 43 to imidazolinone 47 at 63 g/ha preemergence

43

FUCN

47

R= H


43

47

Soybeans Wheat Velvetleaf Ragweed Morningglory Field Bindweed Quackgrass Wild Oats Purple Nutsedge Foxtail Barnyardgrass

0 11 78 0 22 100 67 22 89 78 67

17 33 89 44 67 100 100 67 100 89 78

Table VII. Comparison of cyanoimidazolinone 43 to imidazolinone 47 at 125 g/ha postemergence

43

R = CN

47

R=H

% Injury or % Control Species Soybeans Velvetleaf Ragweed Wild Mustard Morningglory Field Bindweed Quackgrass Wild Oats Purple Nutsedge Foxtail Barnyardgrass

43

47

0 67 44 100 78 100 78 33 89 100 100

44 100 89 100 89 89 67 78 44 100 100


7. GUACIARO ET AL.


69


Table VIII compares the para-methoxybenzyl esters 44 and 48 at 63 g/ha postemergence. Cyanoimidazolinone 44 was more effective in overall broadleaf control and significantly safer on soybeans and corn. A comparison of allyl ester 45 to its parent 49 at 32 g/ha preemergence (Table IX) shows that cyanoimidazolinone 45 was less effective than 49 in controlling quackgrass and barnyardgrass but was superior to 49 in terms of corn safety. We discovered that esters of the cyanoimidazolinones are unstable under conditions which do not normally affect the imidazolinones. When 41 was treated with dilute sodium hydroxide at room temperature in hopes of hydrolyzing the methyl ester, hydrolysis and ring opening occurred, affording acid diamide 50.

41

50

When 41 was applied in the field postemergence to wild oats and wheat at 50 g/ha it showed excellent control of wild oats and complete safety on wheat, outperforming its imidazolinone counterpart. Sixteen to nineteen weeks after treatment, the plots were planted with rape and sugarbeets. Four weeks later the plots showed much injury to the sugarbeets and rape. These results indicate that methyl ester 41 was undergoing little if any breakdown in the soil after 20-23 weeks. The instability of this cyanoimidazolinone at elevated pH is not an indication of reduced soil persistence. We have evidence that suggests that the rate of breakdown or half-life of the imidazolinone esters is related to the nature of the ester and also to the substituents on the aryl ring (unpublished data, American Cyanamid Co., Agricultural Research Division). We are currently studying the rates of breakdown of other esters in the cyanoimidazolinone area with various substituents on the pyridine ring to determine if any compounds show the required combination of excellent weed control, crop selectivity and reduced soil persistence. Synthesis: Acid Salts. It was thought that the free acids or acid salts in the cyanoimidazolinone area might be more susceptible than their esters to breakdown in the plant and/or soil (Figure 1). A great deal of time was spent on trying to prepare the acids from various esters of cyanoimidazolinones or from the parent imidazolinones. The method which was found to be most successful is shown below.




Table VIII. Comparison of cyanoimidazolinone 44 to imidazolinone 48 at 63 g/ha postemergence

44

R = CN

48

R=H


44

48

Soybeans Corn Wheat Velvetleaf Ragweed Wild Mustard Morningglory Field Bindweed Quackgrass Wild Oats Purple Nutsedge Foxtail Barnyardgrass

11 22 11 89 67 100 67 100 44 22 44 100 44

61 40 6 89 51 89 48 94 0 100 73 100 73

Table IX. Comparison of cyanoimidazolinone 45 to imidazolinone 49 at 32 g/ha preemergence

45

R = CN

49

R= H


45

49

Corn Velvetleaf Ragweed Morningglory Field Bindweed Quackgrass Wild Oats Purple Nutsedge Foxtail Barnyardgrass

0 78 11 78 100 44 89 89 100 22

33 100 22 89 100 89 100 100 100 100



7. GUACIARO ET AL.


71

Treatment of tricycle 51 with the sodium salt of trimethylsilylethanol afforded trimethylsilylester 52 in 44% yield after chromatography. Treatment of 52 with sodium hydride followed by cyanogen bromide afforded 53 in 97% yield. Cleavage of the trimethylsilylethyl ester was accomplished with tetrabutylammonium fluoride at room temperature, affording 54 in quantitative yield. The use of anhydrous cesium fluoride or anhydrous potassium fluoride in place of tetrabutylammonium fluoride gave no reaction. Conventional methods of dissociating tetrabutylammonium salts of carboxylic acids, such as dilute hydrochloric acid, concentrated hydrochloric acid, acidic alumina or acidic ion exchange resins failed with the cyanoimidazolinones, affording either recovered salt or decomposition. The free acids could be isolated by passing the salts through dry column silica gel packed in conventional gravity columns. The salts were also shown to dissociate to varying extents on reversed phase HPLC.

Biological Activity: Acid Salts. Table X compares cyanoimidazolinone 54 to imazethapyr 55 preemergence at 32 g/ha. Cyanoimidazolinone 54 was less effective than 55 in conttolling ragweed, morningglory and foxtail but was safer on corn and showed no injury to soybeans. At 63 g/ha postemergence (Table XI), 54 was just as effective as imazethapyr in overall weed control, with the exception of wild oats, and was safer on soybeans.




Table X. Comparison of cyanoimidazolinone 54 to imazethapyr 55 at 32 g/ha preemergence


54

55

Corn Soybeans Ragweed Morningglory Velvetleaf Wild Mustard Field Bindweed Foxtail Barnyardgrass Quackgrass Purple Nutsedge

11 0 0 0 67 100 100 22 78 89 78

22 0 44 89 89 100 100 100 67 100 100

Table XI. Comparison of cyanoimidazolinone 54 to imazethapyr 55 at 63 g/ha postemergence


54

55

Soybeans Ragweed Morningglory Velvetleaf Field Bindweed Foxtail Barnyardgrass Wild Oats Purple Nutsedge

5 67 89 100 100 100 100 44 78

17 78 100 100 100 100 100 67 89



7. GUACIARO ET AL.


73

The free acids showed no significant advantage over their salts in terms of herbicidal activity in the greenhouse. Cyanoimidazolinone 54 was subjected to soil persistence tests in the greenhouse in which pots which had been sprayed with 54 were reseeded with sorghum 30 days after soil application at various rates. The same was done with pots which had been treated with imazethapyr. The reseeded pots that had originally been sprayed with cyanoimidazolinone 54 showed no significant sorghum injury. When cyanoimidazolinone 54 was applied in the field to soybeans postemergence at various rates, the weed control in the plots sprayed with 54 was significantly less than in those sprayed with imazethapyr 55. These results suggest that 54 was undergoing facile breakdown to non-herbicidal compounds in the field too rapidly. Conclusions The N-hydroxyimidazolinones were synthesized via novel chemistry but did not show any significant advantage over their imidazolinone counterparts in terms of herbicidal activity or crop selectivity. The N-chloroimidazolinones showed excellent herbicidal activity in some cases, but have given no indication to date that they break down more rapidly than their parent imidazolinones to non-toxic species in the soil. The N-cyanoimidazolinones, on the other hand, showed good combinations of weed control and crop safety while showing the potential for reduced soil persistence. We have evidence that indicates that certain N-cyanoimidazolinones are less stable than their parent imidazolinones in the greenhouse and in the field. Literature Cited 1. 2. 3. 4. 5. 6.

7.

8. 9. 10. 11.

Los, M.; Ciarlante, D. R.; Ettinghouse E. M.; Wepplo, P. J., 184th National Meeting, American Chemical Society, 1982; PEST 21. Los, M.; Orwick, P. L.; Russell, R. K.; Wepplo, P. J., 185th National Meeting, American Chemical Society, 1983; PEST 87. Los, M., 186th National Meeting, American Chemical Society, 1983; PEST 65. Los, M.; American Chemical Society Symposium Series1984,255,29-44. Los, M.; Wepplo, P. J.; Russell, R. K.; Lences, B. L.; Orwick, P. L., 188th National Meeting, American Chemical Society, Philadelphia, PA, 1984. Los, M.; Wepplo, P. J.; Parker, E. M.; Hand, J. J.; Russell, R. K.; Barton, J. M.; Withers, G.; Long, D. W., 10th International Congress of Heterocyclic Chemistry, University of Waterloo, Canada, 1985. Guaciaro, M. A.; Los, M.; Russell, R. K.; Wepplo, P. J.; Lences, B. L.; Lauro, P. L.; Umeda, K.; Marc, P. A., American Chemical Society Symposium Series1987,355,87-99. Los, M., Proc. Int. Congress Pesticide Chem. 6th, 1986, 35-42. Tseng, S.-S.; Girotra, R. N.; Cribbs, C. M.; Sonntag, D. L. P.; Johnson, J. J., American Chemical Society Symposium Series1991,443,122-132. Los, M. U.S. Patent 4 188 187, 1980. Los, M. U.S. Patent 4 297 128, 1981.


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12. 13. 14. 15. 16. 17. 18. 19. 20. 21.

22. 23. 24. 25. 26. 27. 28.


Los, M. Eur. Patent 41 623, 1981. Los, M. Eur. Patent 133,310, 1985. Los, M. Eur. Patent133,311,1985. Los, M. Eur. Patent 135,711, 1985. Los, M. Eur. Patent158,000,1985. Los, M. U.S. Patent 4 554 013, 1985. Los, M. Eur. Patent 166 907, 1986. Los, M. G.B. Patent 2 174 395, 1986. Los, M.; Long, D. M.; Withers, G. P. Eur. Patent 205879,1986. Cross, B.; Los, M.; Doehner, R. F.; Ladner, D. W.; Johnson, J. J.; Jung, M. E.; Kamhi, V. M.; Tseng, S.-S.; Finn, J. M.; Wepplo, P. J. Eur. Patent 227,932, 1987. Los, M. U.S. Patent 4 911 747, 1990. Guaciaro, M. A. Eur. Patent 433 655, 1991. Howe, R. K.; Schleppnik, F.M.,J.Het. Chem., 1982,19,721. Liu, K.C.;Shelton, B.; Howe, R., J. Org. Chem.,1980,45,3916. Chiang, Y., J. Org. Chem., 1971, 36, 2146. Peake, C. J.; Strickland, J. H., Syn. Comm.,1986,16(7),763. Hussein, A. Q.; El-Abadelah, M. M.; Sabri, W. S., J. Het. Chem., 1984, 21, 455.

R E C E I V E D April 17, 1992


Synthesis and Chemistry of Agrochemicals III - American Chemical

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