Functionalization of Intramolecular Frustrated Lewis Pairs by 1,1‐Carboboration with Conjugated Enynes |
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Authors: | Dr Andreas Feldmann Dr Gerald Kehr Dr Constantin G Daniliuc Dr Christian Mück‐Lichtenfeld Prof?Dr Gerhard Erker |
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Institution: | Organisch‐Chemisches Institut der Universit?t Münster, Corrensstr. 40, 48149 Münster (Germany) |
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Abstract: | The vicinal P/B frustrated Lewis pair (FLP) Mes2PCH2CH2B(C6F5)2 undergoes 1,1‐carboboration reactions with the Me3Si‐substituted enynes to give ring‐enlarged functionalized C3‐bridged P/B FLPs. These serve as active FLPs in the activation of dihydrogen to give the respective zwitterionic P]H+/B]H? products. One such product shows activity as a metal‐free catalyst for the hydrogenation of enamines or a bulky imine. The ring‐enlarged FLPs contain dienylborane functionalities that undergo “bora‐Nazarov”‐type ring‐closing rearrangements upon photolysis. A DFT study had shown that the dienylborane cyclization of such systems itself is endothermic, but a subsequent C6F5 migration is very favorable. Furthermore, substituted 2,5‐dihydroborole products are derived from cyclization and C6F5 migration from the photolysis reaction. In the case of the six‐membered annulation product, a subsequent stereoisomerization reaction takes place and the resultant compound undergoes a P/B FLP 1,2‐addition reaction with a terminal alkyne with rearrangement. |
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Keywords: | boron carboboration frustrated Lewis pairs hydrogen Nazarov cyclization |
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