Meso allylic 1,2-diol

The catalytic enantioselective desymmetrization of meso compounds is a powerful tool for the construction of enantiomerically enriched functionalized products." Meso cyclic allylic diol derivatives are challenging substrates for the asymmetric allylic substitution reaction owing to the potential competition of several reaction pathways. In particular, S 2 and 5n2 substitutions can occur, and both with either retention or inversion of the stereochemistry. In the... 

Trost and co-workers have explored asymmetric transidon metal-catalyzed allylic alkyla-dons. Details on this subject have been well reviewed by Trost and others. With the use of asymmetric palladium-catalyzed desymmetrizadon of meso-2-ene-l,4-diols, cii -l,4-dibenzoy-loxy-2-cyclopentene can be converted to the enandometrically pure cii -4-rfirr-butoxycar-bamoyl-l-methoxycarbonyl-2-cyclopentene. The product is a usefid and general building block for synthesis of carbocyclic analogs of nucleosides as presented in Scheme 5.12. 

As summarized in Schemes 12.9 and 12.10, kinetic resolution of propargylic [21] and allylic [22] alcohols work equally well. The DMAP-ferrocene hybrid 21c was also used for kinetic resolution of racemic diols and for the desymmetrization of meso diols [20]. These two applications are discussed in Section 13.3. 

Resolution by transesterification. Using vinylic acetates to esterify allyl alcohols, propargyl alcohols, 2-phenylthiocycloalkanols, a-hydroxy esters," methyl 5-hydroxy-2-hexenoates, and 2-substituted 1,3-propanediols, the enantioselective esterification provides a means of separation of optical isomers. Vinyl carbonates are also resolved by lipase-mediated enantioselective conversion to benzyl carbonates. Other esters that have also been used in the kinetic resolution include 2,2,2-tri-fluoroethyl propionate. There is a report on a double enantioselective transesterification" of racemic trifluoroethyl esters and cyclic meso-diols by lipase catalysis. 

A cyclic allylic azide is required for a synthesis of (-i-)-pancratistatin. This intermediate is obtainable from a Pd-catalyzed reaction of MCjSiNj with a meso-2-cyclohexene-l,4-diol dicarbonate in the presence of a chiral ligand. 

The allylic amination also proceeds in intramolecular fashion. The meso-diol (10.106) forms an intermediate (10.107), which undergoes enantioselective cy-clisation with high enantioselectivity to give the product (10.108). The use of... 

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