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Lithium Amino Alkoxide–Evans Enolate Mixed Aggregates: Aldol Addition with Matched and Mismatched Stereocontrol
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posted on 2018-02-19, 05:36 authored by Janis Jermaks, Evan H. Tallmadge, Ivan Keresztes, David B. CollumBuilding
on structural and mechanistic studies of lithiated enolates
derived from acylated oxazolidinones (Evans enolates) and chiral lithiated
amino alkoxides, we found that amino alkoxides amplify the enantioselectivity
of aldol additions. The pairing of enantiomeric series affords matched
and mismatched stereoselectivities. The structures of mixed tetramers
showing 2:2 and 3:1 (alkoxide-rich) stoichiometries are determined
spectroscopically. Rate and computational studies provide a viable
mechanistic and stereochemical model based on the direct reaction
of the 3:1 mixed tetramers, but they raise unanswered questions for
the 2:2 mixed aggregates.
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enantioselectivitylithiated enolatesacylated oxazolidinonesaggregatealkoxidealkoxide-richLithiumpairingchiral lithiatedEvans enolatesstoichiometriestereoselectivitieMismatched Stereocontrol BuildingAggregatestereochemical modelAldol AdditionMatchedMixedtetrameraldol additionsAlkoxideEnolateenantiomeric seriesspectroscopicallyAmino
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