Transition-Metal-Free Redox-Neutral One-Pot C3-Alkenylation of Indoles Using Aldehydes

Abstract

The synthesis of sensitive β-alkyl 3-vinylindoles having diverse functional groups with good selectivity remains a challenging task. Keeping the synthetic utility of 3-alkenylindoles in mind, we explored a unique approach to synthesize them from unprotected indoles in a domino fashion. A transition-metal-free C3-alkenylation of indole is reported by using sequential Brønsted acid/base catalysis. Several β-substituted 3-alkenylindoles and conjugated 1,3-dienes are synthesized by direct coupling of indole and readily available aliphatic aldehydes. Excellent scalability and recycling of benzenesulfinic acid for successive alkenylation reactions up to five times make this method economically viable.

Central‐to‐Axial Chirality Conversion Approach Designed on Organocatalytic Enantioselective Povarov Cycloadditions: First Access to Configurationally Stable Indole–Quinoline Atropisomers

“…Compound 2 b , featuring a methyl group at position 2 of the indole, was found to be poorly suitable for the Povarov reaction with 1 a , delivering the corresponding product 3 ab in low yield and enantioselectivity (entry 2). Oxidation of this compound afforded configurationally stable quinoline 4 ab , although with no retention of the enantiomeric excess.…”

Cobalt(III)‐Catalyzed Construction of Benzofurans, Benzofuranones and One‐Pot Orthogonal C−H Functionalizations to Access Polysubstituted Benzofurans

“…Although, single directing group promoted two‐fold C−H activations are well documented, one‐pot, orthogonal C−H functionalizations are scarce . In our continuous efforts to develop one‐pot sequential catalytic methods,– herein amide‐directed two‐fold orthogonal C−H functionalizations are reported by employing two different electrophiles. The major challenge to execute this method is to get the desired regioselectivity in our product.…”

Regioselective Direct C‐Alkenylation of Indoles

“…Temporary exchange of the hydroxy group initially formed in the Friedel–Crafts reaction with a better leaving group such as the phenylsulfonyl system allows to obtain 3‐alkenylated indoles in a one‐pot procedure (Scheme ) . A wide range of aldehydes can be used in this process, including alkanals and β,γ‐unsaturated aldehydes which provide an efficient synthesis of 3‐dienyl derivatives.…”

“…Te mporary exchange of the hydroxy group initially formed in the Friedel-Crafts reaction with ab etter leavingg roup such as the phenylsulfonyl system allows to obtain 3-alkenylated indoles in ao ne-pot procedure (Scheme 88). [176] Aw ide range of aldehydes can be used in this process, including alkanals and b,g-unsaturated aldehydes which provide an efficient synthesis of 3-dienyl derivatives. The whole procedure is based on the well-known chemistry of sulfonylindoles 113 which are formed by exchange of the hydroxy group in the initially formed alco-hol 112 by phenylsulfinica cid.…”