Interrupted carbonyl-olefin metathesis via oxygen atom transfer

Abstract

Some of the simplest and most powerful carbon-carbon bond forming strategies take advantage of readily accessible ubiquitous motifs: carbonyls and olefins. Here we report a fundamentally distinct mode of reactivity between carbonyls and olefins that differs from established acid-catalyzed carbonyl-ene, Prins, and carbonyl-olefin metathesis reaction paths. A range of epsilon, zeta-unsaturated ketones undergo Brønsted acid–catalyzed intramolecular cyclization to provide tetrahydrofluorene products via the formation of two new carbon-carbon bonds. Theoretical calculations and accompanying mechanistic studies suggest that this carbocyclization reaction proceeds through the intermediacy of a transient oxetane formed by oxygen atom transfer. The complex polycyclic frameworks in this product class appear as common substructures in organic materials, bioactive natural products, and recently developed pharmaceuticals.

Superelectrophilic Aluminum(III)-Ion Pairs Promote a Distinct Reaction Path for Carbonyl-Olefin Metathesis of Medium-Sized Rings

“…6a,6f Only those that provide extended aromatic products (2) proceed in comparably high yields to their 5-membered homologs. 6b, [10][11][12] Furthermore, competing Lewis acid-catalyzed carbonyl-ene reactions have proven challenging to control and result in diminished yields of the desired metathesis products. Our recent efforts aimed at ex- panding the scope of carbonyl-olefin metathesis reactions have shown that FeCl3 monomers (6) can associate in situ 13 to form Lewis acidic superelectrophiles 14 (7).…”

Superelectrophilic Aluminum(III)-Ion Pairs Promote a Distinct Reaction Path for Carbonyl-Olefin Metathesis of Medium-Sized Rings

“…6a,6f Only those that provide extended aromatic products (2) proceed in comparably high yields to their 5-membered homologs. 6b, [10][11][12] Furthermore, competing Lewis acid-catalyzed carbonyl-ene reactions have proven challenging to control and result in diminished yields of the desired metathesis products. Our recent efforts aimed at ex- panding the scope of carbonyl-olefin metathesis reactions have shown that FeCl3 monomers (6) can associate in situ 13 to form Lewis acidic superelectrophiles 14 (7).…”

Catalytic Carbonyl-Olefin Metathesis of Aliphatic Ketones: Iron(III) HomoDimers as Lewis Acidic Superelectrophiles

“…3) Recent investigations of Brønsted acid-catalyzed oxygen atom transfer reactions have shown that alternate oxetane fragmentation pathways exist competing with carbonyl-olefin metathesis reactions. 9 Specifically, acidic protons in the α-position to the carbonyl functionality can engage in distinct oxetane fragmentation pathways under acid-catalyzed conditions forming the corresponding unsaturated alcohols 10 via elimination ( Fig. 2C).…”