INOR 7 |
| In the ring-opening polymerization of cyclic esters such as lactide, LA, by metal alkoxide catalysts trans-esterification is often a competing non-desirable reaction. Trans-esterification occurs by both inter-chain and intra-chain processes and the latter leads to cycles (LA/2)n. In this work a polymer supported lithium alkoxide catalyst is employed to effect ROP and in benzene at +70ºC cyclic esters (LA/2)n are released to the solution in a reversible manner generating a dynamic combinatorial library of rings. The introduction of NaBPh4 selectively removes the 18-membered rings as (CHMeC(O)O)6NaBPh4. In this way 3 equiv of LA are converted to (CHMeC(O)O)6 in >80% yield. The rings can be separated by chromatography and one each of the six enantiomeric pairs together with the two meso isomers have been characterized along with several complexes with NoBPh4. 2,5-morpholinediones show selective trans-esterification at the ester ketonic group leading to rings of size nx6. |
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Frontiers in Organometallic Chemistry
8:25 AM-12:00 PM, Sunday, August 19, 2007 BCEC -- 206 A/B, Oral
Division of Inorganic Chemistry |