Optically Active 1-Hydroxyalkylphosphonates IVB and

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. 

Based on these two asymmetric synthetic approaches, a new route was designed and used to synthesize optically active 1-hydroxyalkylphosphonates in our laboratory [57]. A series of optically active 1-hydroxyalkylphosphonates was 

The base-catalysed hydrophosphonylation of aldehydes or imines (Pudovik reaction) [58] as a convenient method was widely used for the synthesis of 1-hydrox-yalkylphosphonates. Since the pioneering work of Shibuya [50] and Spilling [51] was reported, much attention has been devoted to developing enantioselective catalysts for the synthesis of chiral 1 -hydroxy alkylphosphonates. Chiral aluminium complexes were shown to be more effective chiral catalysts [59-62]. Based on the success of using A1 (salen) and A1 (salcyen) as asymmetric catalysts, Al-Schiff base complexes [63, 64] have been developed to catalyze the asymmetric addition reaction of dial-kylphosphonates and aldehydes. Tridentate Schiff base metal complexes, such as vanadium, chromium, and iron [65], have been successfully applied in many asymmetric synthetic reactions. We noticed that Al(III) complexes could catalyse the asymmetric Pudovik reaction and these ligands could be easily synthesized [66-70]. 

However, the steric hindrance of substituent R and R had a minor effect on reactivity (81-84 % yield. Table 6.1, entries 1-8). Products IVB-1 could retain the same absolute configuration with ligands LI in this reaction. The (5) or (R) IVB-1 with the same ee value could be obtained in this reaction by using corresponding ligands with the same absolute configuration (5)-Ll or (R)-Ll (Table 6.1, entries 5-8). 

The relationship between the enantiomeric excess of Schiff base ligand and the product was tested by Feng and co-workers [63]. The results indicated that there was a strong positive nonlinear effect, which implied that the reaction occurred due to the presence of a polymeric aluminium active species. The presence of dimeric 

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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... 

The structures, physicochemical data, and yields of optically active cyclic 1-hydroxyalkylphosphonates IVB are listed in Table 9.42. 

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