Photoredox-Enabled Synthesis of β-Substituted Pyrroles from Pyrrolidines

Quinoline as an Intramolecular Hydride Shuttle in the Deoxygenative Coupling Reaction of Alcohol and the Inert Methyl C(sp3)-H Bond

Reported herein is the C(sp3)-C(sp3) bond-forming at an unactivated C(sp3)-H bond via hydride transfer-initiated deoxygenative coupling reactions. Various polycyclic hydroquinolines were provided under metal-free conditions with excellent diastereoselectivity. Mechanistic study revealed that quinoline served as an intramolecular hydride shuttle to achieve the hydride abstraction and release in order. This methodology not only provides a practical strategy for direct deoxygenative coupling for the C(sp3)-C(sp3) bond-forming but also develops a new reaction type involving quinoline-enabled hydride transfer.

Substituent-Dependent, Switchable Synthesis of Nonaromatic and Aromatic Heterocyclic Sulfones Using Visible Light

In this Letter, we described a visible-light-induced switchable synthesis of nonaromatic and aromatic sulfonyl heterocycles. The product selectivity between 2,5-dihydropyrrole and pyrrole can be tuned by altering the substituent on the N atom of 1,6-diyne. We highlight the intricacy and efficiency of this approach in constructing molecular frameworks under mild conditions with a high functional group tolerance. This study elucidates the mechanism underlying product selectivity, highlighting its potential as a compelling alternative to traditional synthetic techniques.

B(C6F5)3-Catalyzed Dehydrogenation of Pyrrolidines to Form Pyrroles

Pyrroles are important N-heterocycles found in medicines and materials. The formation of pyrroles from widely accessible pyrrolidines is a potentially attractive strategy but is an underdeveloped approach due to the sensitivity of pyrroles to the oxidative conditions required to achieve such a transformation. Herein, we report a catalytic approach that employs commercially available B(C6F5)3 in an operationally simple procedure that allows pyrrolidines to serve as direct synthons for pyrroles. Mechanistic studies have revealed insights into borane-catalyzed dehydrogenative processes.

Visible-Light-Induced Dual C(sp3)-H Bond Functionalization of Tertiary Amine via Hydrogen Transfer to Carbene and Subsequent Cycloaddition

Herein, we describe the dual C(sp³)-H bond functionalization of a tertiary amine through hydride-transfer-induced dehydrogenation, followed by cycloaddition, using an easily preparable diazoester as a new type hydride-acceptor precursor under mild, redox-neutral conditions. With carbene as a hydrogen acceptor, this method was demonstrated by the preparation of a broad range of functionalized isoxazoldines in moderate to good yields.

Catalyst-free direct regiospecific multicomponent synthesis of C3-functionalized pyrroles

An operationally simple catalyst-free protocol for the direct regiospecific synthesis of β-(C3)-substituted pyrroles has been developed. The enamine intermediate, in situ generated from succinaldehyde and a primary amine, was trapped with activated carbonyls before the Paal-Knorr reaction in a direct multicomponent "just-mix" fashion to furnish pyrroles with overall good yields. Several C3-substituted N-alkyl/aryl/H pyrroles have been produced under open-flask conditions with high atom economy and avoiding protection-deprotection chemistry.

Direct catalytic synthesis of β-(C3)-substituted pyrroles: a complementary addition to the Paal-Knorr reaction

The synthesis of β-(C3)-functionalized pyrroles is a challenging task and requires a multistep protocol. An operationally simple direct catalytic synthesis of β-substituted pyrroles has been developed. This one-pot multicomponent method combined aqueous succinaldehyde as 1,4-dicarbonyl, primary amines, and isatins to access hydroxyl-oxindole β-tethered pyrroles. Direct synthesis of the β-substituted free NH-pyrrole is the central intensity of this work. DFT-calculations and preliminary mechanism investigation support the possible reaction pathway.