Lecture13outline-1

Lecture13outline-1 - I. Review Numerous variations on the...

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I. Review • Numerous variations on the Claisen rearrangement have been developed • The Cope rearrangement is an all carbon version, but in general the driving force is not high • Exceptions occur when the rearrangement proceeds with strained ring cleavage (nice way to make 7- and 8-membered rings) and when a hydroxyl group is appended to one of the sp 3 -hybridized carbons (oxy-Cope rearrangement) • The oxy-Cope rearrangement proceeds to form an enol that tautomerizes to yield an aldehyde or ketone • The anionic oxy-Cope is sufficiently driven to proceed at room temperature because reactive itermediates weaken appended carbon–carbon bonds • Adding an alkoxy group to Claisen substrates leads to ester formation following rearrangement • Claisen, Cope, and related reactions proceed through 6-membered chair-like transition states that can be used to predict stereochemical outcomes when substituted alkenes are used • This transition state predicts that relative stereochemistry can be changed by changing
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Lecture13outline-1 - I. Review Numerous variations on the...

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