By Alfred Hassner

Enantioselective man made tools should not in basic terms within the leading edge of chemical and pharmaceutical study yet task during this region is continually expanding. it's influenced by means of the urgency to acquire medications or compounds of medicinal curiosity as unmarried anantiomers, and the keeness to synthesize usual items in nonracemic shape. This quantity offers seven chapters from pioneers and professionals during this swiftly increasing box.

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Jpn. ; Yamamoto, Y. J. Org. ; Yamamoto. Y Tetrahedron Utt. 35,8425; (d) Asao. ; Tsukada. ; Yamamoto. , Chem Commun. 1993, 1660; (e) Yamamoto. ; Uyehara, T. J. Anu Chenu Soc. ; Uyehara, T; Yamamoto, Y. ; Yamamoto, Y. J. , Chenu Commun. 1989. 753; (h) Asao. ; Uyehara. T; Yamamoto. Y Tetrahedron 1988. ; Yamamoto. y. , Chenu Commun. 1410. 8. (a) Rathke. M. W; Sullivan. D. Tetrahedron Utt. 4249; (b) Herrmann. J. ; Kieczykowski, G. ; Schlessinger. R. H. Tetrahedron Utt. 1973, 2433. 9. Little. R. ; Dawson.

RMB. ' RMB. R 1 2 Scheme 1. g. g. g. g. e. deprotonation of cyclic ketones having C^ symmetry with chiral lithium amide bases, will be the focal point of this account. g. ^^'^^ A more complete, although still simplistic, picture of the reaction is shown in Scheme 2. The lithium amide behaves as a Lewis acid and complexes to the C = 0 group to form 4. Proton transfer via a cyclic transition state follows and another complex 5 is generated (only one of the two different possible regio- or diastereoisomeric forms of 5 is shown; transfer of H,^ would, of course, generate the other isomer).

In all three systems non-racemic products were observed and the selectivity ranged from modest to good. As is common when developing a new enantioselective reaction the choice of the model compound(s) was critical. The three model ketones were clearly selected for their structural simplicity. Our model was the worst, because it required a nontrivial synthesis. The choice of the electrophile is also important and the electrophile should enter into a high- yielding reaction and the product should allow measurement of the enantiomeric excess by a reasonably simple protocol, preferably on a crude product, prior to purification which might affect the enantiomer ratio.

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