Study on Stereocontrol in Sigmatropic Rearrangement

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i) Anti-selective [2, 3] Wittig rearrangementIn the course of the study on stereocontrol of sigmatropic rearrangements, we found that [2, 3] Wittig rearrangement of 2' -heterosubstituted alpha-alkenyloxyacetic acid esters exhibited unusual anti-selectivity as shown below. The origin of this unusual stereoselectivity was attributed to the steric repulsion of a ligand on the counter metal ion and a C2' -substituent and to interaction of lone pair orbital on oxygen atom and sigma^* -orbital of C2 -carbon and hetero atom bond.ii) Preparation of concave-shaped ligands and their application to kinetic resolution of dl-epoxy alcohols.Concave-shaped ligands (1 and 2) were prepared from L-alanine and their titanium complexes were used for kinetic resolution of dl-epoxy alcohols as Lewis acid catalyst. As shown in the following scheme, kinetic resolution of 3, 3-disubstituted epoxy alcohols using a combination of Ti (OPr^i) 4 and 1a was found to proceed with high efficiency.Further study on ester enolate Claisen rearrangement via titanium enolate wherein titanium ion carries 1 as a ligand, is under investigation.