Cu(I)-Catalyzed Cross-Coupling Rearrangements of Terminal Alkynes with Tropylium Tetrafluoroborate: Facile Access to Barbaralyl-Substituted Allenyl Acid Esters and 7-Alkynyl Cycloheptatrienes

Abstract

Herein, we report a novel strategy for the formation of copper carbene via the cycloisomerization of the π-alkyne–Cu­(I) complex from terminal alkynes and tropylium tetrafluoroborate. Mechanistic studies and DFT calculations indicate that the reaction undergoes the intramolecular cycloisomerization process from the π-alkyne–Cu­(I) complex to afford the copper carbene intermediate, followed by migratory insertion with the second terminal alkyne to afford the barbaralyl-substituted allenyl acid esters. In addition, we develop a mild and highly efficient Cu­(I)-catalyzed cross-coupling protocol to synthesize 7-alkynyl cycloheptatrienes that has a broad functional group tolerance and is applicable to the late-stage functionalization of natural products.

Modulating Escape Channels of Cycloheptatrienyl Rhodium Carbenes to Form Semibullvalene

“…83 Cu(I) catalysts similarly have been shown to work in a synthesis of barabaralyl-substituted allenyl acid esters from terminal alkynes and tropylium tetrafluoroborate. 84 Finally, during preparation of this manuscript, Dumele and Teichert published an intriguing synthesis of 6p and 10p neutral homoaromatics. 63 Their synthetic approach, inspired by the work of Vogel et al, 62 affords homoannulene esters with a barbaralone framework through an intramolecular, dearomative Buchner reaction.…”

Modulating Escape Channels of Cycloheptatrienyl Rhodium Carbenes To Form Semibullvalene

“…82 Cu(I) catalysts similarly have been shown to work in a synthesis of barabaralyl-substituted allenyl acid esters from terminal alkynes and tropylium tetrafluoroborate. 83 Finally, Dumele and Teichert published an intriguing synthesis of 6π and 10π neutral homoaromatics during preparation of this manuscript (Scheme 1e). 62 Their synthetic approach, inspired by the work of Vogel et al, 61 affords homoannulene esters with a barbaralone framework through an intramolecular, dearomative Buchner reaction.…”

“…When the Echavarren group expanded on this work in 2021, they discovered that the use of Rh­(II)-catalysts led to a decarbenation to alkynylcyclopropanes from 7-alkynyl cycloheptatrienes and attributed the result to a lower barrier for decarbenation (Δ G ‡ = 21.9 kcal mol –1 ) than for 6- endo -dig cyclization (Δ G ‡ = 24.4 kcal mol –1 ) with the use of Rh­(II) catalysts . Cu­(I) catalysts similarly have been shown to work in a synthesis of barabaralyl-substituted allenyl acid esters from terminal alkynes and tropylium tetrafluoroborate . Finally, Dumele and Teichert published an intriguing synthesis of 6π and 10π neutral homoaromatics during preparation of this manuscript (Scheme e) .…”