Phospha-Claisen Type Reactions at Frustrated Lewis Pair Frameworks

Area of Science:

• Organophosphorus Chemistry
• Lewis Pair Chemistry
• Organic Synthesis

Background:

• Frustrated Lewis pairs (FLPs) are reactive species formed from Lewis acids and bases that do not form classical adducts.
• Unsaturated phosphane/borane FLPs have shown promise in catalyzing various organic transformations.
• The reactivity of C4-bridged phosphane/borane FLPs with unsaturated carbonyl compounds remains an area for exploration.

Purpose of the Study:

• To investigate the reaction of C4-bridged unsaturated phosphane/borane FLPs with acetylenic esters and ketones.
• To elucidate the formation of heterocyclic intermediates and their subsequent rearrangement products.
• To explore potential anomalous reaction pathways and mechanistic insights.

Main Methods:

• Reaction of phosphane/borane FLPs with various acetylenic esters and ketones.
• Characterization of reaction intermediates and products using spectroscopic methods.
• X-ray diffraction analysis of key compounds to confirm structures.

Main Results:

• Formation of 10-membered heterocyclic intermediates containing allyl phosphonium/allenic enolate functionalities.
• Subsequent phospha-Claisen type rearrangement yielding substituted phosphanyl pentadienes.
• Observation of two exceptional cases involving cyclopropane ring formation and carbon-carbon bond activation.

Conclusions:

• C4-bridged unsaturated phosphane/borane FLPs are effective in the synthesis of novel heterocyclic compounds.
• The study reveals a versatile synthetic route to substituted phosphanyl pentadienes via phospha-Claisen rearrangement.
• Anomalous reaction pathways highlight the complex reactivity of FLPs and offer new avenues for synthetic exploration.