) attacks the carbonyl carbon from the least hindered side—the side exposing the Small group ( ), rather than the Medium group (

Key concepts

Evans oxazolidinones used to control enolate alkylations and aldol reactions.

Reveals an α,β-unsaturated ester conjugated with a ketone (cross-conjugated system). The large J=16 Hz indicates trans alkene, but the two carbonyls are not in conjugation with each other—forces you to distinguish between dienone and enone ester.

Advanced stereochemistry involves stereoselective and stereospecific reactions, including chiral auxiliaries and catalysts.

(Context: A cyclopentane ring with an alcohol and a methyl group on adjacent carbons transforming into a cyclohexanone derivative). Step-by-Step Mechanism

Find the rich and poor electron centers.

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