Hydroxyalkyl and Epoxyalkyl Acids

5 Hydroxyalkyl and Epoxyalkyl Acids. - The reaction most widely adopted for the preparation of (l-hydroxyalkyl)phosphonic esters is that attributed to Abramov and involves the interaction of hydrogenphosphonates with aldehydes or ketones, sometimes in the presence of a base catalyst. The same reaction has now been shown to be catalysed by mineral phosphates e.g. fluoroapatite. The same process, catalysed by the complex (134) [(R)-form] gives the same esters in 50-95% yields and with 55-9d% e.e.s The study of the diastereoselective phosphonoylation of aldehydes using chiral 1,3,2-diazaphospholidine reagents has continued with an examination of the use of the stereoisomers of (135), which 

Reagents i, ii, HCI, MeaCO iii, NaBH4, CeCb-ZHaO. MeOH  

The use of silyl phosphite esters in the Abramov reaction is well established, but a practical modification involves the addition of MesSiCl to a mixture of triethyl phosphite and carbonyl reactant at room temperature. The addition of a silyl phosphite (R = Si-containing group) to a chiral hydroxyaldehyde derivative (138) (R is also a Si-containing group) affords a mixture of the diprotected diastereoisomeric (l,2-dihydroxyalkyl)phosphonic esters (139) and 

The enantioselective reduction of diethyl (2-oxoalkyl)phosphonates with Sac-charomyces cerevisiae can be achieved with good results up to 100% e.e.s were obtained in some cases. In a series of examples, reductions of the esters (141) (X = mono- or di-halogen. Me, MeO, NO2, MeS, or MeS02) by the boranes 

Racemic (l-acetyloxyalkyl)phosphonic diesters may be enantioselectively hydrolysed in biphasic systems containing a lipase from Aspergillus niger, although selectivity is reduced if the alkyl chain in the substrate is branched. The resultant acids and esters of opposite chirality) are separable, and the unreacted 

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Hydroxyalkyl and Epoxyalkyl Acids. Lipase-catalysed acylation of ethyl(l-hydroxyalkyl)phenylphosphinates (249) and (250) afforded a single diastereoisomer of the corresponding acetates (251) in high enantiomeric excess (>98%) (Figure 46). °... 

Hydroxyalkyl and Epoxyalkyl Acids. The addition of organometallic (Zn or Mg) reagents to p-ketophosphonates (233) offers a new route to p-hydroxyphos-phonates (234) containing a tertiary alcohol function. Yields are variable, excellent in the best cases, and can be improved in the Grignard examples by the addition of BF3.Et20. What is claimed to be the first catalytic asymmetric... 

Hydroxyalkyl and Epoxyalkyl cicfs.-Some worthwhile developments have occurred in the synthesis of (1-hydroxyalkyl)phosphonic acid derivatives through the so-called... 

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