Frustrated Lewis Pair‐Catalyzed Cycloisomerization of 1,5‐Enynes via a 5‐endo‐dig Cyclization/Protodeborylation Sequence

Abstract

The first frustrated Lewis pair-catalyzed cycloisomerization of a series of 1,5-enynes was developed. The reaction proceeds via the π-activation of the alkyne and subsequent 5-endo-dig cyclization with the adjacent alkene. The presence of PPh3 was of utmost importance on the one hand to prevent side reactions (for example, 1,1-carboboration) and on the other hand for the efficient protodeborylation to achieve the catalytic turnover. The mechanism is explained on the basis of quantum-chemical calculations, which are in full agreement with the experimental observations.

Geminal bis-borane formation by borane Lewis acid induced cyclopropyl rearrangement and its frustrated Lewis pair reaction with carbon dioxide

“…It is known that cyclopropanes are often readily opened to the respective olefin isomers upon exposure to boron Lewis acids. 10 Therefore, we briefly checked whether the opened isomer of 5b , 2-methyl-1-buten-3-yne, might be involved in this reaction. However, this was not the case.…”

Structure–Reactivity Relationship in the Frustrated Lewis Pair (FLP)‐Catalyzed Hydrogenation of Imines

“…The application of frustrated Lewis pairs (FLP) has grown immensely since their first report to activate molecular hydrogen (H 2 ) in the absence of transition metals . The development of new FLP‐catalyzed reactions is in the focus of contemporary research resulting in spectacular transformations, for example, the activation of strong C−F bonds, cross‐couplings, or cycloisomerizations . However, the fundamental understanding of FLP reactivity with the aim to establish a structure–reactivity relationship is in its infancies.…”

Boron‐Based Catalysts for C−C Bond‐Formation Reactions

“…Interestingly, Grimme et al. showed that the 1 /PPh 3 FLP catalyzed the 5‐ endo cyclization of 39 to give functionalized indenes 41 ; this was previously reported with a gold catalyst by the group of Sanz (Scheme ) …”