Dearomatization of tryptophols via a vanadium-catalyzed asymmetric epoxidation and ring-opening cascade

Abstract

An enantioselective epoxidation of tryptophols followed by an intramolecular epoxide opening reaction was realized by chiral vanadium catalysts derived from C2 symmetric bis-hydroxamic acid (BHA) ligands. 3a-Hydroxyfuroindoline derivatives with up to 89% yield and 90% ee were obtained under mild reaction conditions.

Catalytic Asymmetric Dearomatization by Transition-Metal Catalysis: A Method for Transformations of Aromatic Compounds

“…A vanadium-based catalyst supported by a chiral bishydroxamic acid (BHA) ligand L23, originally invented by Yamamoto 86 for asymmetric epoxidation of allylic and homoallylic alcohols, was successfully transplanted to the tryptophol systems (Scheme 27). 87 This reaction tolerates a relatively broad scope of substrates. Substrates bearing substituents at different positions of the indole ring, including C2 and N1, undergo the reaction smoothly under mild conditions (toluene, À10 C).…”

“…85Scheme 27. V-Catalyzed Asymmetric Oxidative Dearomatization of IndolesOriginally reported by the Zhang and You group 87,88. …”

Electrooxidation enables highly regioselective dearomative annulation of indole and benzofuran derivatives

“…In these cases, most of the strategies took advantage of the C2-C3 π bond or the inherent strong nucleophilicity of C3 position, and had the advantage of rapid construction for highly functionalized indoline frameworks in one step. On the other hand, recent advances in oxidation-induced C-H functionalization have opened up other possibilities for constructing various polycyclic indolines [27][28][29][30][31] . In this regard, many efficient strategies for activating indoles have been developed under mild conditions [32][33][34][35][36] .…”

Vanadium(V) Complex-Catalyzed One-Pot Synthesis of Phenanthridines via a Pictet-Spengler-Dehydrogenative Aromatization Sequence

“…We theorized that these functionalities can be used to perform domino reaction sequences in a single operation. Furthermore, there are a few reports on the cooperative effect of vanadium(V) complexes in synthesis [24][25][26][27][28]. Recently, we developed chiral oxovanadium complexes [29] that act as redox and/or Lewis acid catalysts for the enantioselective oxidative coupling of arenols [30][31][32][33], Friedel-Crafts-type reactions [34], and a sequential cascade reaction that affords oxahelicenes [28].…”