Enantioselective Synthesis of Allenes by Catalytic Traceless Petasis Reactions
journal contributionposted on 25.01.2017, 14:18 by Yao Jiang, Abdallah B. Diagne, Regan J. Thomson, Scott E. Schaus
Allenes 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