Synthesis of Alkynylmethylidene‐benzoxasiloles through a Rhodium‐Catalyzed Cycloisomerization Involving 1,2‐Silicon and 1,3‐Carbon Migration

Abstract

It is shown that ac ationic rhodium(I)/biphep complex catalyzest he cycloisomerization of 2-(alkynylsilylethynyl)phenols,leading to alkynylmethylidene-benzoxasiloles through concomitant silicon and carbon migration. This unprecedented cycloisomerization presumably proceeds via the formation of rhodium vinylidenes through 1,2-silicon migration, followed by 1,3-carbon (alkyne) migration via the formation of hypervalent silicon centers.

Transition Metal Vinylidene- and Allenylidene-Mediated Catalysis in Organic Synthesis

“…Cycloisomerization of dialkynylsilanes has recently been reported by the Tanaka group, invoking a mechanism related to that of alkyne dimerization (Scheme 164). 394 When treated with a cationic rhodium(I)−BIPHEP catalyst at room temperature, dialkynylsilane 815 was converted to cyclic enyne 816 in good yield. The authors propose that facile Cto-O silyl migration (815 to 817), induced by rhodium coordination, sets the stage for the generation of vinylidene intermediate 818, from which a sequence involving alkynyl addition and protodemetalation produces enyne 816.…”

Synthetic strategies to access silacycles

“…On the other hand, alkynylsilanes can also undergo 1,2silicon migration under transition metal-catalytic systems (Kanno et al, 2016). Employing these reaction characteristics, Tanaka reported an Rh(I)/biphep complex catalyzeed cycloisomerization of 2-(alkynylsilyl-ethynyl)phenols 110, leading to the formation of alkynylmethylidene-benzoxasiloles 111 through concomitant silicon and carbon migration (Namba et al, 2017). This novel cycloisomerization possibly proceeds via the formation of Rh-vinylidenes through 1,2-silicon migration, followed by 1,3-carbon (alkyne) migration via the formation of hypervalent silicon centers (Scheme 13E).…”