Enol phosphonates

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. 

The hydrolytic products are benzyl alcohol and the corresponding enol phosphonate produced through carboxyl group participation. In the presence of hydroxylamine the products are diverted to benzyl phenylphosphonate and pyruvate oxime hydroxamate. These experimental results contrast markedly with those observed for the phosphoacetoin system. A simple explanation for the formation of benzyl phenylphosphonic acid is generation of the penta-covalent species (47)... 

The chiral bis(oxazoline)/Cu(II) complex with OTf or SbFg as a counter anion effectively promotes the enantioselective hetero Diels-Alder reaction of enol ethers with acyl phosphonates to give chiral enol phosphonates as synthetically useful chiral building blocks [64] (Eq. 8A.40). 

In conclusion, C-C bond formation on carbohydrates has absorbed lots of widely used methods from general synthetic organic chemistry. Typical among these methods are intramolecular alkylation and intramolecular condensation of aldehyde with enolates, phosphonates, and nitro-stabilized anions. Metal-mediated radical reactions, cycloadditions, and rearrangements have also been applied frequently. 

M min ), of 181 compared to nerve gas VX is about 1.3 x 10 -fold weaker. It is noteworthy that cyclic enol phosphonates are modest irreversible AChE inhibitors and exhibit attractive characteristics as potential anti-Alzheimer drugs. 

Finally, the palladium-catalyzed cross-coupling reactions with supported enol phos-phonates were reported by Steel and coworkers (Table 1.13, Entry 1) Polymer-supported lactam enol phosphonates were prepared and multifunctional cleavage was demonstrated, using Suzuki conditions, to provide aryl enamines in good yields. 

Sasaki etal have utilized RCM to generate the seven-membered ciguatoxin A-ring (Scheme 3.41) [50]. From the intact B-D subunit 212 that was synthesized using a novel enol phosphonate alkyl Suzuki coupling sequence, RCM using [Ru]-I catalyst gave tetracycle 213. 

A new series of customisable diastereomeric ds-and trans-monocyclic enol-phosphonate analogues to Cyclophostin (471) and Cyclipostins (472) has been synthesised (Scheme 160). Their potencies and mechanisms of... 

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