Copper phosphonate groups

Copper Lewis acids have also found utility in hetero-Diels-Alder reactions. In these transformations the Lewis acid can activate either the diene or the dienophile and both types of reaction have been reported. Evans et al. have evaluated unsaturated acyl phosphonates [95] and acyl esters (amides) [87] as dienes in hetero-Diels-Alder reactions. The reactions proceed with excellent chemical efficiency and high stereoselectivity with as little as 0.2 mol % of the catalyst (Sch. 50). The reaction tolerates a variety of substituents on the diene and the dienophile. A square-planar model 226 wherein the phosphonate and the carbonyl groups form a chelate with copper, and addition occurring from the less hindered face, accounts for the selectivity observed. It is interesting to note that the reaction of 185 with phosphonate 228 gives 230, an inverse-electron-demand product, in preference to the normal Diels-Alder adduct 229. This unusual reaction pathway has been attributed to the electron-withdrawing capacity of the phosphonate group. 

The copper complex of these bis(oxazoline) compounds can also be used for hetero Diels-Alder reactions of acyl phosphonates with enol ethers.43 5 A favorable acyl phosphonate-catalyst association is achieved via complexation between the vicinal C=0 and P=0 functional groups. The acyl phosphonates are activated, leading to facile cycloaddition with electron-rich alkenes such as enol ethers. The product cyclic enol phosphonates can be used as building blocks in the asymmetric synthesis of complicated molecules. Scheme 5-36 shows the results of such reactions. 

Benzene may be polymerized under the action of aluminium chloride and copper chloride into a thermostable structure which retains the chemical reactivity of benzene. Such a polymer may be sulfonated or phosphonated in suspension, and active acidic catalysts are obtained that are stable up to 350 °C and carry the functional groups only at the surface n°) ... 

Within this area, the most recent developments in the synthesis of esters of phosphonic acids have been the direct alkylation of hydrogenphosphonates using diazoalkanes in the presence of copper-containing catalysts in benzene as the solvent Of those catalysts examined, the most effective seem to be [Cu(acac)2] and [Cu(OTf)2], with Cu, Pd and Rh acetates and [Ni(acac)2] being less effective. The overall reaction is that represented in equation 18, in which R and R may be H, Ph or a simple alkyl group, but they may also consist of a functionalized alkyl group in reactions catalysed by trifluoromethanesul-phonic acid A similar procedure has been applied to the hydrogenphosphinate Ph(MeO)P(0)H ... 

A more unusual leaving group (H) was employed in copper-catalyzed aerobic phosphonation of sp C-H bonds in an isoquinoline derivative (Scheme 68). A speculative mechanism involving nucleophilic attack on a Cu-complexed imine was proposed [121]. 

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