Convergent Synthesis of Azabicycloalkenones using Squaric Acid as Platform

Abstract

Abstract:The synthesis of azabicycloalkenones bearing a vinylogous amide moiety was achieved by means of the rhodium-catalyzed decarbonylative cycloaddition of cyclobutenediones with a pendant alkene. The starting cyclobutenediones were efficiently prepared from appropriate squaric acid monoesters and N-benzylalkenylamines under microwave heating conditions.

Divergent Syntheses of Fused β‐Naphthol and Indene Scaffolds by Rhodium‐Catalyzed Direct and Decarbonylative Alkyne–Benzocyclobutenone Couplings

“…Although the direct decarbonylation of cyclobutanones to give cyclopropanes (ring contraction) has been known for almost two decades since the seminal work by Murakami, Ito, and co-workers, [19] C À C cleavage with subsequent decarbonylation and insertion of an unsaturated moiety has been much underdeveloped. The intermolecular decarbonylative couplings of cyclobutenediones and cyclobutenones with norbornene and ethylene were first reported by Kondo, Mitsudo, and co-workers, [8] and the only example of an intramolecular coupling of squaric acid derivatives and olefins was described by Yamamoto et al [9] However, to the best of our knowledge, the decarbonylative coupling between any cyclic ketones and alkynes was previously unknown. [20] The proposed decarbonylative "cut and sew" transformation (Scheme 2 B) was explored using 1 l as the model substrate.…”

“…[6,7] Thus, complementary to the direct insertion reaction (regular "cut and sew"), the corresponding decarbonylative "cut and sew" would provide an [X + Y-1]-type coupling by extruding CO from the substrate to give the fused ring D (Scheme 1), a process which remains largely elusive. [8,9] Herein, we describe our efforts in developing a divergent approach to realize both regular and decarbonylative "cut and sew" transformations through rhodium-catalyzed intramolecular couplings between benzocyclobutenones [10] and alkynes (Scheme 2 B). The resulting bnaphthol and indene fused-ring products provided by this approach are useful synthetic building blocks, [11] and have also been found in a number of biologically important molecules ( Figure 1).…”

Regioselective Activation of a Sterically More Hindered C−C Bond of Biphenylenes Using an Alkene as Both a Directing Group and a Reaction Moiety

“…They elucidated the reaction mechanism based on the DFT calculations: selective cleavage of less hindered and more reactive C−C bond is followed by isomerization of rhodacycle through decarbonylation and carbonylation . Yamamoto and co‐workers developed a synthesis of bicycloalkenones from squaric acids possessing alkenyl tethers: selective C−C bond activation was achieved through the bidentate coordination of ketone and a hetero atom, or a diketone as a directing group. Although directing groups containing hetero atoms have the potential to cleave a C−C bond in a diastereoselective manner, they are typically difficult to remove after the reaction .…”

Ruthenium‐ and Rhodium‐Catalyzed Strain‐Driven Cleavage and Reconstruction of the C–C Bond

“…[80] Yamamoto has since reported the Rh I -catalyzed intramolecular and decarbonylative alkene insertion into cyclobutenediones to give azabicycloalkenones. [81] Eur. J. Org.…”