Functionalization of Intramolecular Frustrated Lewis Pairs by 1,1-Carboboration with Conjugated Enynes.
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.
Organisch-Chemisches Institut der Universität Münster, Corrensstr. 40, 48149 Münster (Germany).
Andreas
A
Feldmann
Organisch-Chemisches Institut der Universität Münster, Corrensstr. 40, 48149 Münster (Germany).
Gerald
G
Kehr
Organisch-Chemisches Institut der Universität Münster, Corrensstr. 40, 48149 Münster (Germany).
Constantin G
CG
Daniliuc
Organisch-Chemisches Institut der Universität Münster, Corrensstr. 40, 48149 Münster (Germany).
Christian
C
Mück-Lichtenfeld
Organisch-Chemisches Institut der Universität Münster, Corrensstr. 40, 48149 Münster (Germany). erker@uni-muenster.de.
Gerhard
G
Erker
Nazarov cyclization; boron; carboboration; frustrated Lewis pairs; hydrogen