Cyclic 1-hydroxyalkylphosphonates

As stated in Chap. 2, several series of open-chain 0,0-dialkyl 1-hydrox-yalkylphosphonates M2 have been prepared and studied. In order to examine the herbicidal activity of phosphorus-containing heterocyclic 1-hydroxyalkylphosph-onate and their derivatives, firstly two series of cyclic 1-hydroxyalkylphosphonates including 2-(l-hydroxyalkyl)-5,5-dimethyl-4-pheny-l,3,2-dioxaphosphinane-2-ones IVA and 2-(l-hydroxyalkyl)-5,5-dimethyl-l,3,2-dioxaphosphinane-2-ones IVB were synthesized. 

In the IVA and IVB series, further modification was focused on substituent R. In this section, we describe the synthesis and herbicidal activity of cyclic 1-hydroxyalkylphosphonates, IVA and IVB. The results of preliminary bioassay indicated that IVA and IVB exhibited certain herbicidal activity. 

Cyclic 1-hydroxyalkylphosphonates IVA and IVB could be synthesized by Pudovik reaction (Scheme 5.2) [41]. Cyclic 1-hydroxyalkylphosphonates IVA were prepared by hydrophosphonylation of various aldehydes with 5,5-dimethyM-phenyl-l,3, 2-dioxaphosphinane-2-one M18-1 in the presence of triethylamine as a basic catalyst. The cyclic phosphonate M18-1 could be easily prepared by the reaction of... 

A series of cyclic 1-hydroxyalkylphosphonates IVA including 12 compounds was prepared. The structures of IVA are listed in Table 5.1. 

The cyclic 1-hydroxyalkylphosphonates IVB were synthesized using a similar process to IVA. Neopentyl glycol reacted with 1 equiv. of phosphorus trichloride in... 

Detailed synthetic procedures for cyclic 1-hydroxyalkylphosphonates IVA and IVB are introduced in the Sect. 9.1.23 of Chap. 9. The structures of IVA and IVB were established by well-defined IR, NMR, and elemental analysis. IVA-3 (R = 4-ClPh) was further analyzed by X-ray single-crystal difliraction. Spectroscopic analyses of some representative IVA and IVB are given in Sect. 5.1.3. 

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. 

Since cyclic 1-hydroxyalkylphosphonates IVB were easily decomposed at a high temperature and phosphonates IVC-IVF containing carboxylic acid ester groups were also very sensitive to acid, base or water. Therefore the reaction required a moderate control of temperature. The reagents and solvents should be preprocessed in anhydrous state. The reaction was carried out in three stages firstly, a solution of substituted phenoxyacetyl chloride was added dropwise to the solution of cyclic 1-hydroxyaIkylphosphonate under 5 °C secondly, the reaction solution was stirred at room temperature for several hours, and then at a higher temperamre for further reaction in 1-2 h. By above synthetic method, 57 of cyclic phosphonates including IVC (23 compounds), IVD (13 compounds), IVE (13 compounds), and... 

Compared with clacyfos (IC-22, HW02), IVD-12 exhibited a shghtly higher herbicidal effect against broad-leaved weeds, leaf mustard or common amaranth, and also showed much higher herbicidal activity against monocot weeds than that of clacyfos. However, cyclic 1-hydroxyalkylphosphonates IVA and IVB had no significant herbicidal activity (Sect. 5.1.5). All cyclic phosphonates IVC were also not comparable to clacyfos. 

The 1-hydroxyalkylphosphonates and cyclic 1-hydroxyalkylphosphonates can be used as very useful synthetic intermediates of open-chain or cyclic alkylphosphonates. Therefore 1-hydroxyalkylphosphonates and cyclic 1-hydroxyalkylphosphonates as the key intermediates of our tide compounds were first studied. According to the reports, two asymmetric synthetic methods could be considered to prepare 1-hydroxyalkylphosphonates. 

The base-catalyzed hydrophosphonyladon of aldehydes as a convenient method is widely used for the synthesis of chiral 1-hydroxyalkylphosphonates. We have developed an eflftcient and steroselective method for the synthesis of optically active 1-hydroxyalkylphosphonates and cyclic 1-hydroxyalkylphosphonates by asymmetric hydrophosphonyladon using Al-Schiff base complexes as catalysts. The addition of silver carbonate was found to enhance this catalytic reaction rate significantly. Under optimized reaction conditions, several optically active cyclic 1-hydroxyalkylphosphonates IVB including (S) and (R) configuration could be prepared by the asymmetric hydrophosphonyladon of aldehydes with corresponding cyclic phosphonates in 77-82 % yields with 99 % enantioselectivity. A series... 

Cyclic 1-hydroxyalkylphosphonates IVA and IVB could be synthesized by hy-drophosphonylation of various aldehydes with cyclic phosphonates M18 in the presence of triethylamine as a basic catalyst (Scheme 9.23). 

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). 

Cyclic 1-hydroxyalkylphosphonates IVB were synthesized asymmetrically via enantioselective hydrophosphonylalion of aldehydes using tridentate SchiflF base A1 (III) complexes as catalysts (Scheme 9.29). 

Scheme 9.29 Synthesis of optically active cyclic 1-hydroxyalkylphosphonates IVB...

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