Caged Bicyclic Phosphates IVG and IVH

Heterocyclic compounds containing a symmetric caged bicyclic phosphate have received much attention since they were first synthesized by Verkade and Re3molds in 1960 [51]. Several of these compounds with useful biological activity had been reported [52-64]. 

In the series of IVG, further modification was focused on substituent Y . On the basis of caged bicyclic phosphate IVG, substituted phenoxyacetyl moiety in IVG was modified into substimted phenox3 propionyl moiety to produce a series of IVH. In the series of IVH, O or S as X was kept constant respectively, further modification was focused on substituent Y . 

In this section, the synthesis and herbicidal activity of series IVG and IVH are described, and their stmcture-activity relationships are discussed. 

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Since a carboxylic acid ester bond which is sensitive to acid, base or water, is contained in caged bicyclic phosphate IVG and IVH, this synthetic reaction required moderate temperamre and weak base. Reagents and solvents needed to be preprocessed in anhydrous state. 

Table 5.34 Inhibitory activity of caged bicyclic phosphates IVG and IVH against the growth of plants ...

Caged bicyclic phosphate IVG and IVH could be conveniently synthesized by the condensation of 4-(hydroxymethyl)-2,6,7 -trioxa-1 -phosphabicyclo[2.2.2]octane 1-oxide M21 or 4-(hydroxymethyl)-2,6,7-trioxa-l-phosphabicyclo[2.2.2]octane 1-sulfide M22 and substituted phenoxyacetyl chlorides M5 or substituted phen-oxypropionyl chlorides M20 in the presence of triethylamine as a base (Scheme 9.28). 

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. 

Scheme 1.32 Design of cyclic phosphonates IVA-IVF and caged bicyclic phosphates IVG-IVH...

In this chapter, we focus on the synthesis, herbicidal activity, and stmcture-activity relationship of cyclic phosphonates IVA-IVF, and caged bicyclic phosphates IVG-IVH. Indeed, the bioassay results showed that several cyclic phosphonates exhibited promising herbicidal activity and potential utility as herbicides. 

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