Synthesis of Polyheterocyclic Tropones by [2 + 2 + 2 + 1] Carbonylative Cycloaddition of Triynes

Abstract

A direct synthesis of tropones (2,4,6-cycloheptatrienes) from simple preorganized triynes has been elaborated. This simple rhodium-catalyzed domino strategy allows one-pot access to fully substituted tropones in a 6-6-7-5 tetracyclic core in average to high yields.

Synthesis of Aromatic Rings Embedded in Polycyclic Scaffolds by Triyne Cycloaddition: Competition between Carbonylative and Non-Carbonylative Pathways

“…Scheme 3 summarizes the proposed mechanism for carbonylative cycloaddition, cyclotrimerization and cyclotrimerization/elimination processes based on previous studies [17,30]. It is unsure if the dimeric pre-catalyst first undergoes ligand exchange with CO to form catalytic species [RhCl(CO) 3 ] or if the coordination bond with the bridging chloride is preserved.…”

“…This mechanism allows the rationalization of the observed reaction rates depending on the length of the tethers. The formation of C and C′ are possible overnight at room temperature with tethers leading to the formation of 5-membered rings, yet the reaction is sluggish when this tether is homologated [17].…”

“…In the course of our work on the synthesis of polycyclic compounds containing 7- and 8-membered rings [13,14,15,16], we recently interested ourselves in the Rh I -catalyzed [2+2+2+1] carbonylative cycloaddition of pre-organized triynes yielding 2,4,6-cycloheptatrienones (Scheme 1a) [17]. These compounds, more commonly referred as tropones [18], are non-benzenoid aromatic carbonylated 7-membered rings that have attracted increasing attention due to their interesting electronic properties [19,20,21], their presence in several natural products [22,23], and their 8π system, which gives them importance as synthons [24].…”

Recent Advances in the Synthesis of 5‐MemberedN‐Heterocycles via Rhodium Catalysed Cascade Reactions

“…Synthesis of polyheterocyclic tropones by [2 + 2 + 2 + 1] carbonylative cycloaddition of triynes. [132] 231 and seven-membered 1,4-oxazepine compounds 232 in moderate to excellent yields under mild reaction conditions. The plausible mechanistic steps include generation and nucleophilic addition of rhodium carbene species A to quinoline producing intermediate B.…”

“…Reductive elimination of the former led to the desired tropone 219 (Scheme 63). [132] Over the past decade cyclopropylidene has been progressively accepted as three or two carbon units in transitionmetal-catalyzed [3 + 2 + 2] and [2 + 2 + 2] cycloadditions, respectively. [133a-h] Enantioselective [3 + 2 + 2] and [2 + 2 + 2] cycloadditions of two monoynes or a 1,6-enynes by cyclopropylidene compounds was previously reported by Saito and co-workers by utilizing Nickel(0)/Phosphine complex as catalyst.…”