Lecture19outline

Lecture19outline - I Review The Evans aldol reaction...

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I. Review • The Evans aldol reaction proceeds to form the syn-product (hydroxyl and alkyl groups on the same side of the alkyl chain) as a consequence of the enolate geometry • The Zimmerman-Traxler transition state predicts that changing the enolate geometry will result in the anti-product being formed, which is observed • Absolute stereocontrol results from the benzyl group on the acyl substituent blocking one face of the enolate • The alkene fragment of α , β -unsaturated aldehydes and ketones can undergo reactions that would not be possible in the absence of the carbonyl group • The unusually downfield 1 H NMR chemical shifts of the β -hydrogen indicate that the β - carbon of α , β -unsaturated ketones should be electrophilic, in accord with an analysis of resonance structures • Conjugation provides enhanced stability for α , β -unsaturated ketones and aldehydes relative to the β , γ -unsaturated isomers β , γ -unsaturated ketones and aldehydes can be converted to their
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This note was uploaded on 05/17/2010 for the course CHEM 0740 taught by Professor Professor during the Spring '10 term at Pittsburgh.

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Lecture19outline - I Review The Evans aldol reaction...

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