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ABSTRACT:The water-soluble calix [4]

Anhydrous potassium monoalkyl phosphonates have been prepared from the corresponding dialkyl phosphonates and potassium trimethylsilanolate under non-aqueous conditions in good to excellent yields. Simple workup procedure has been developed to afford high purity products.Potassium trimethylsilanolate is a common equivalent of hydroxide anion. It has two unique advantages over hydroxide anion: (i) It has appreciable solubility in organic solvents and (ii) the oxygen silicon bond can be very often easily cleaved under mild reaction conditions. Despite these unique properties, trimethylsilanolates have been mainly reported in a narrow range of reaction, e.g. as polymerisation initiators, 1 as bases to promote elimination of MeOH from b-methoxyketones, 2 in the deprotection of propyne iminium salts, 3 and as a hydroxyl synthon for fluoride S N Ar-type displacement from certain activated aromatics. 4 The most valuable synthetic applications of alkali trimethylsilanolates were reported by Merchant for conversion of nitriles to primary amides, 5 by Laganis and Chenard for preparation of anhydrous carboxylate salts from the corresponding esters and acid chlorides. 6 We have found that potassium trimethylsilanolate is very effective in the conversion of esters with large steric hindrance to corresponding carboxylate salt or acid. 7 Here, we report the use of potassium trimethylsilanolate (KOTMS) to convert dialkyl phosphonates to their anhydrous potassium monoalkyl phosphonates.Base-mediated hydrolysis of dialkyl phosphonates to their monoalkyl phosphonic acid alkali metal salts requires drastic experimental conditions (high pH and prolonged heating times). This method cannot be applied to compounds possessing other base-sensitive functional groups. We have found that treatment of wide range of dialkyl phosphonates with potassium trimethylsilanolate in either anhydrous THF, Et 2 O or CH 2 Cl 2 affords corresponding potassium monoalkyl phosphonates with high purity and yield (Scheme 1). Scheme 1The developed method has two major advantages: firstly, the reaction can be performed in the presence of other functional groups and secondly, as the potassium salts precipitate from Et 2 O, any impurities can be conveniently washed away. The results are summarized in the Table 1.The reaction of calix[4]arene phosphonates with potassium trimethylsilanolate (Table 1, entries 1-4) afforded corresponding potassium monomethyl calix[4]arene phosphonates in excellent yields (84-98%). In contrast, the aqueous basic hydrolysis gave complicated mixture of mono-and dimethyl phosphonates and purification could not be accomplished.The presence of a-protons does not interfere with the desired reaction (entries 5 and 9-16). In particular, we were concerned with proton abstraction from triethyl phosphonoacetate (pK a 11.89, lit. 8 ), but in this case (entries 11-14) KOTMS behaves as a nucleophile rather than a base.The treatment of dimethyl dithiophosphonates (entries 7 and 8) afforded corresponding potassium thiophosphonates in very good yield. T...

Organo-phosphorus compoundsOrgano-phosphorus compounds S 0080 Calix[4]arene Phosphonates -Recognition of Amino Alcohols in Water. -(WITT, D.; DZIEMIDOWICZ, J.; RACHON*, J.; Heteroat. Chem. 15 (2004) 2, 155-161; Dep. Org. Chem., Tech. Univ. Gdansk, PL-80-952 Gdansk, Pol.; Eng.) -K. Schneider 31-138