Cyclic Alkylphosphonates IVC-IVF

Through the stody on the alkylphosphonates lA-IK series, it was found that higher herbicidal activity and inhibitory activity against plant PDHc El could be achieved by introducing small groups (Me) as R and R in the structure lo. This result 

As stated in Sect. 5.1, cyclic 1-hydroxyalkylphosphonates IVB exhibited certain herbicidal activity in the preliminary bioassay, and therefore it was expected that cyclic phosphonates IVC-IVF might be more active than the corresponding cyclic 1-hydroxyalkylphosphonates IVB. 

WhenH as R remained the same, substituted phenyl, furyl or alkyl as was introduced into the parent structure of IV to form the IVC, IVD, and IVE series, respectively. In the IVC, IVD, and IVE series, substituted phenyl, furyl or alkyl as R was kept constant, respectively further modification was focused on substituent Y . In the IVF series, methyl as R and R was kept constant, further modification was also focused on substituent 

In this section, the synthesis and herbicidal activity of the IVC-IVF series are described, and their structure-activity relationships are discussed. 

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Cyclic alkylphosphonates IVC-IVF could be conveniently prepared by the condensation of cyclic 1-hydroxyalkylphosphonates IVB with substituted phenoxy-acetyl chlorides MS or phenoxypropionyl chlorides M20 in the presence of triethylamine as a base (Scheme 9.26). 

The structures, physicochemical data, and yields of cyclic alkylphosphonates IVC-IVF are listed in Tables 9.36, 9.37, 9.38 and 9.39, respectively. 

Several different types of cyclic phosphonates IVA-IVF were designed on the basis of the alkylphosphonates lo. Moreover, the cyclic phosphonates IVC-IVF were further modified to the caged bicyclic phosphates IVG-IVH (Scheme 1.32). It was expected that herbicidal activity of compounds could be optimized by introducing a phosphorus-containing heterocyclic moiety. 82 of cyclic phosphonates IVA-IVF and 27 of caged bicyclic phosphates IVG-IVH hence were prepared. 

As mentioned in Chap. 2, several series of open-chain 1-(substituted phenoxy-acetoxy)aLkylphosphonates were found to exhibit notable herbicidal activity against dicotyledons. In order to examine the effect of phosphorus-containing heterocyclic moiety on herbicidal activity, a phosphorus-containing six-member ring was introduced into different molecules to form cyclic phosphonates IVC-IVF. A set of experiments were performed to evaluate their herbicidal activity. The herbicidal activity of cyclic phosphonates IVC-IVF are reviewed as follows. 

As mentioned before, quite a few of 0,0-dialkyl 1-(substituted phenoxyacetoxy) alkylphosphonates such as open-chain phosphonates lA—IK and cyclic phosphonates IVA-IVF as racemate have been synthesized in our laboratory. Some of these racemates in the lA-IJ and IVC-IVE series exhibited significant herbicidal activity. In order to examine the characteristics of two enantiomers of these race-mates, we made an effort to set up an efficient synthetic method to prepare two enantiomers of these racemates including lA-IJ and IVC-IVE series. 

General procedure A solution of substituted phenoxyacetyl chlorides M5 or phenoxypropionyl chlorides M20 (0.01 mol) in dichloromethane (15 mL) was added dropwise to the stirred mixture of appropriate 2-(hydroxy(substituted) methyl)-5,5-dimethyl-l,3,2-dioxaphosphinan-2-one IVB (0.01 mol) and triethylamine (0.011 mol) in dichloromethane (20 mL) under 5 °C, the reaction solution was stirred at room temperature for 2—4 h, and then at 40 °C for another 1-2 h. The resultant mixture was washed with 0.1 M hydrochloric acid solution, saturated sodium bicarbonate solution and brine separately, dried and evaporated. The residue was chromatographed on silica with ethyl acetate/petroleum ether (1/3) as eluent to give the corresponding cyclic alkylphosphonate as a white or yellowish solid. AU IVC-IVF series could be obtained by this procedure. 

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