Imidazolinone

The inhibitors of amino acid synthesis, sulfonylureas, imidazolinones, and glyphosate, were first recognized as general growth inhibitors that prevent mitotic entry (188,189). Whatever the mode of action, herbicides that inhibit amino acid synthesis also cause a rapid inhibition of cell growth, usually through inhibition of mitotic entry. 

Aldehydes and ketones react with azolinones. The reaction between aldehydes and 2-phenyl-5-oxazolinone (131 Y = H), formed in situ from PhC0NHCH2C02H and AC2O, gives azlactones (131 Y = RCH). Similar reactions are given by 4-thiazolidinones, e.g. (132) gives (133) (79AHC(25)83), and 4-imidazolinones. In pyrazolin-5-ones the 4-position is sufficiently activated for condensation to occur with ketones in acidic media (Scheme 8) (66AH06)347). 

Uncharged azoles not containing oxygen or sulfur are often resistant to attack by hydroxide ions at temperatures up to 100 °C and above. However, neutral azoles react with hydroxide ions under extreme conditions, e.g. 1-substituted imidazoles such as (153) at 300°C give the corresponding imidazolinone (154) 80AHC(27)24l). 

Although imidazolinones are usually resistant to hydrolysis, oxazolinone rings are often easily opened. In acid-catalyzed reactions of this type, water converts azlactones (181) into a-acylamino-a,/3-uhsaturated acids (182) (77AHC(21)175). 1,3,4-Oxadiazolinones are readily opened by hot water to give hydrazine carboxylic acids which undergo decarboxylation. 

Propargyl alcohol (332) and (328) react readily with isocyanates in the presence of a basic catalyst to give 4-methylene-2-oxazolidinones (334) and 4-methylene-2-imidazolinones (336), respectively (63JOC991). In the absence of sodium methoxide the intermediate methanes (333) and ureas (335) were obtained and on treatment with sodium methoxide underwent ring closure. Moderate to excellent yields were obtained. 

Imidazolin-2-one, 1,5-diphenyl-4-aryl-synthesis, 5, 492 4-Imidazolin-2-one, 1-hydroxy-synthesis, 5, 474—475 4-Imidazolin-2-one, l-methyl-3-phenyl- C NMR, 5, 355 Imidazolinones acylation, 5, 424, 443 alkylation, 5, 443 developers... 

Imidazolinones diazo coupling, 5, 424 Mannich reaction, 5, 405 reactions, 5, 442... 

Plan of Study to Determine the Occurrence of Sulfonylurea, Sulfonamide, and Imidazolinone Herbicides in Surface and Ground-Water of the Midwestern United States. US Geological Survey, Washington, DC (1998). Also available on the World Wide Web http //webserver.cr.usgs.gov/midconherh/html/workplan98.html, accessed September 2002. 

Sample preparation consists of homogenization, extraction, and cleanup steps. In the case of multiresidue pesticide analysis, different approaches can have substantially different sample preparation procedures but may employ the same determinative steps. For example, in the case of soil analysis, the imidazolinone herbicides require extraction of the soil in 0.5 M NaQH solution, whereas for the sulfonylurea herbicides, 0.5M NaOH solution would completely decompose the compounds. However, these two classes of compounds have the same determinative procedure. Some detection methods may permit fewer sample preparation steps, but in some cases the quality of the results or ruggedness of the method suffers when short cuts are attempted. For example, when MS is used, one pitfall is that one may automatically assume that all matrix effects are eliminated because of the specificity and selectivity of MS. 

One application using MAE is a method to determine imidazolinone herbicides and their respective metabolites in plant tissue." Current residue methodologies for determining imazethapyr (imidazolinone herbicide) and its metabolites in crops involve laborious, time-consuming cleanup procedures after an aqueous/organic extraction. 

Electrospray ionization (ESI) and APCI are the two popular API techniques that will be discussed here. The applications to the analysis of pesticides that will be discussed include imidazolinone herbicides, phenoxy acid herbicides, and A-methyl carbamate insecticides. Matrix effects with respect to quantitation also will be discussed. Eor the... 

ESI performs well for the more polar compounds such as imidazolinone herbicides, sulfonylurea herbicides, triazine herbicides, phenoxy acid herbicides, and carbamate pesticides (to name a few). ESI also performs well with proteins and peptides. 

In another example, a multiresidue method using HPLC/ESI-MS was developed to determine six imidazolinone herbicides in five different soil types. Good recoveries (80-120%) and adequate sensitivity at the 2.0 ngg level were obtained for the compounds investigated. In the method, a 50-g soil sample was extracted for 1 h in 0.5N NaOH solution. A portion of the extract was acidified, to precipitate the humic acids, and the supernatant was then loaded on to a preconditioned trifunctional Cig SPE cartridge and eluted with ethyl acetate. Further cleanup was achieved using a tandem strong anion-exchange (SAX)-SCX SPE combination. Analytes were eluted... 

Table 6 List of ions monitored for imidazolinone herbicides using in-source CID (HPLC/ESI-MS)...

Dehydration converting the imidazolone ring to imidazolinone seems to be sensitive to the aromatic nature of residue 66 [61, 62]. This step is thought to lead to the formation of an enolate intermediate, which can be trapped by reverse anaerobic chemical reduction of the mature chromophore using dithionite and other reducing agents [63]. 

Fig. 3 Protonation states, isomerism and mesomerism of the HBI chromophore (p-hydroxybenzi-lidene-imidazolinone). The chromophore is shown in its most stable Z ( cw ) conformation, conventionally associated to a 0° value of the dihedral angle t, while the E ( trans ) conformation corresponds to t = 180°. For model compound HBDI (4 -hydroxy-benzylidene-2,3-dimethyl-imidazolinone), Ri = R2 = CH3, for chromophore in GFP, Ri, and R2 stand for the peptidic main chains toward N-terminus and C-terminus, respectively, (a) Possible protonation states of HBI (a) neutral, (b) anionic, (c) enolic, (d) cationic, and (e) zwitterionic. (b) Two resonance structures of the anionic form of HBI...

Fig. 4 Absorption spectra of the green type GFP chromophore as a function of pH. (a) Absorption spectra of model compound FIBDI (4-hydroxybenzy lidene-1,2-dimethyl-imidazolinone) in aqueous solution cationic (- 1 M HC1), neutral acetate buffer, pH 5.5), and anionic 1 M NaOFI). Reproduced with permission from [71]. (b) Absorption spectra of AvGFP as a function of pH pH 5.46 (a), pH 8.08 (b), pH 10.22 (c), pH 11.07 (d), pH 11.55 (e), pH 13.0 (f), pH 1.0 (g). For curves (a-e) the buffer contained 0.01 M each sodium citrate, sodium phosphate and glycine. Sample f was in 0.1 M NaOH, and sample g was in 0.1 M HC1. Reproduced with permission from [6],...

Cycloadducts have been successively obtained by reaction of MCP with maleic anhydride (116) and a number of related electron-deficient alkenes (137,486,487) under photolytic conditions in the presence of a sensitizer (Table 38, entries 5-8) [132b]. Analogous cycloadditions in mild conditions with high yields have also been performed with electron-donor substituted alkenes, such as vinylene carbonates 483 and 484 and the imidazolinone 485 (entries 2-4) [132], In the case of the unsymmetrical anhydride 137 (entry 6), an almost equimolar mixture of both the possible regioisomers has been obtained [132b]. In all these cases the reaction has also been proposed to occur via diradical intermediates formed from the reaction of 1 with the alkene in its excited triplet state [132]. 

The 1,3-dipolar cycloaddition of imidazolinone 123 with ethyl m-4,4,4-trifluorocrotonate 124 provided, after 36 h at reflux, the regio- and stereoisomer 125 (90%), accompanied with traces of three other unidentified cycloadducts (10%) <2001JFC275>. Compound 125 was isolated in 70% yield (Scheme 15). The structures of the final product were elucidated by nuclear Overhauser effect (NOE) experiments. This high selectivity is the result of a preferred ///////-orientation of both ester and CF3 groups in the transition state and of an impeded ////////-approach of the CFj-substituted terminus of the alkene to the sterically hindered ct-site of 123. 

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