Gold-Catalyzed Regioselective Synthesis of Crowded Cyclopentadienes by Migratory Cycloisomerization of Vinylallenes

Abstract

We report the regioselective synthesis of silyl-substituted cyclopentadienyl esters through gold-catalyzed migratory cycloisomerization of silyl-substituted vinylallenes. This transformation is proposed to proceed through a perfectly orchestrated sequence of events including Nazarov-like cyclization and several silyl and hydrogen rearrangements. Furthermore, exploiting the multifaceted nature of the gold catalyst, we have also identified suitable conditions for the synthesis of these cyclopentadienes in a more straightforward manner through gold-catalyzed reaction of propargyl esters and alkynylsilanes.

1,2-Silyl Rearrangement in Gold Carbene Chemistry: Synthesis of Furyl-Decorated Tetrasubstituted Silylallene Derivatives

“…Based on our previous findings and related precedents in gold-catalyzed transformations of enynones, − a reasonable catalytic cycle for the formation of furyl-substituted allene derivatives 3 is shown in Scheme . First, coordination of enynone 1 to the gold catalyst followed by 5- exo -dig cyclization would generate gold furyl carbene intermediate I .…”

“…This is the case of alkynes with only a few examples of capture of gold carbenes with these unsaturated substrates . In this context, in 2021, our group reported a gold-catalyzed reaction involving propargyl esters and alkynylsilanes, yielding vinylallene derivatives (Scheme A) . Mechanistically, this transformation would involve: (1) generation of a gold carbene intermediate thorough [1,2]-acyloxy rearrangement, (2) regioselective C–C bond formation by nucleophilic attack of the alkynylsilane to the carbene carbon with formation of a cationic intermediate, and (3) concurrent gold elimination/[1,2]-silyl rearrangement.…”

Amine-Release Annulation of Enaminones: Bimetallic Co-Catalytic Synthesis of Cyclopentadienes from Alkynes

“…The ester group could be easily hydrolyzed under acid conditions to generate 1,4diketone 4ao in 62% yield (Scheme 4a). 21 The keto group of 3ao could be reduced effectively to a hydroxyl group as 5ao in 87% yield, which offers the potential for further functionalization (Scheme 4b). 22 Interestingly, the C�C bond could be chemoselectively oxidized into ketone 6ao in the presence of m-chloroperbenzoic acid (m-CPBA) (Scheme 4c).…”

“…It delivered the corresponding spiro-cyclopentadiene 3ao in 72% yield (1.67 g). The ester group could be easily hydrolyzed under acid conditions to generate 1,4-diketone 4ao in 62% yield (Scheme a) . The keto group of 3ao could be reduced effectively to a hydroxyl group as 5ao in 87% yield, which offers the potential for further functionalization (Scheme b) .…”