Thiiranes chiral initiators polymerization

Fig. 6. Polymerization of methyl thiirane using various chiral initiators. Variation of the optical activ-ity ajj (neat, dm) of residual monomer with conversions. homosteric type process using ZnEtj — (-) -tBu—CHOH—CHjOH (1 1) as initiator system antisteric type process using CdMej —(-) -tBu—CHOH—CH OH (1 1) as initiator system...

Influence of the nature of the initiator Initiators resulting from the reaction between an organometallic derivative and a chiral compound containing an acidic hydrogen were the most usually employed in the stereoelective polymerization of oxiranes and thiiranes. 

For example, in the case of oxiranes and thiiranes one must prepare first the corresponding chiral 1,2 diols, and the overall yields from starting materials to final cyclic monomers are sometimes less than 5%. Price and Osgan [1] were the first to polymerize with different initiators the dextrorotatory propylene oxide. Several other optically active oxiranes and thiiranes were successfully prepared and polymerized [2, 3]. 

Fig. 18. Mechanistic scheme of stereoelectrve polymerization of oxiranes and thiiranes using ZnEtj-chiral-l,2-diol initiator system.

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