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Enantioselective Synthesis of Allenes by Catalytic Traceless Petasis Reactions
journal contribution
posted on 2017-01-25, 14:18 authored by Yao Jiang, Abdallah B. Diagne, Regan J. Thomson, Scott E. SchausAllenes
are useful functional groups in synthesis as a result of
their inherent chemical properties and established reactivity patterns.
One property of chemical bonding renders 1,3-substituted allenes chiral,
making them attractive targets for asymmetric synthesis. While there
are many enantioselective methods to synthesize chiral allenes from
chiral starting materials, fewer methods exist to directly synthesize
enantioenriched chiral allenes from achiral precursors. We report
here an asymmetric boronate addition to sulfonyl hydrazones catalyzed
by chiral biphenols to access enantioenriched allenes in a traceless
Petasis reaction. The resulting Mannich product from nucleophilic
addition eliminates sulfinic acid, yielding a propargylic diazene
that performs an alkyne walk to afford the allene. Two enantioselective
approaches have been developed; alkynyl boronates add to glycolaldehyde
imine to afford allylic hydroxyl allenes, and allyl boronates add
to alkynyl imines to form 1,3-alkenyl allenes. In both cases, the
products are obtained in high yields and enantioselectivities.
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nucleophilic additiontraceless Petasis reactionallyl boronatesalkynyl iminesenantioenriched chiral allenessulfinic acidpropargylic diazenechemical propertiesallenes chiralchiral allenesglycolaldehyde iminereactivity patternsenantioselective methodsenantioselective approachesCatalytic Traceless Petasis Reactions Alleneschiral biphenolsalkynyl boronatesMannich productachiral precursorsaccess enantioenriched allenesallylic hydroxyl allenessulfonyl hydrazonesboronate additionEnantioselective Synthesis
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