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Phospha-Claisen Type Reactions at Frustrated Lewis Pair Frameworks

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posted on 15.06.2016, 00:00 by Guo-Qiang Chen, Gerald Kehr, Christian Mück-Lichtenfeld, Constantin G. Daniliuc, Gerhard Erker
The C4-bridged unsaturated phosphane/borane frustrated Lewis pairs (P/B FLPs) 4 undergo borane induced phosphane addition to a variety of acetylenic esters or ketones to generate heterocyclic 10-membered intermediates that contain pairs of allyl phosphonium/allenic enolate functionalities. These subsequently undergo phospha-Claisen type rearrangement reactions to give the respective substituted phosphanyl pentadiene products. In two exceptional cases subsequent reactions leading to anomalous phospha-Claisen products were found. One example involved cyclopropane ring formation, and the other carbon−carbon bond activation. Potential mechanistic schemes leading to these products are discussed. Essential examples were characterized by X-ray diffraction.