Annulative Nonaromatic Newman-Kwart-Type Rearrangement for the Synthesis of Sulfur Heteroaryls

By employing enaminones and thiuram disulfides as starting materials, the frontiers of Newman-Kwart rearrangement have been expanded to the alkenyl system for the first time. In addition, instead of leading to the formation of simple carbamothioates, the rearrangement has led to the unprecedented construction of S-heteroaryls. Depending on the differences in the enaminone structure, the efficient synthesis of functionalized isothiazoles and thiophenes has been achieved.

Unlock the C-N Bond Amidation of Enaminones: Metal-Free Synthesis of Enamides by Water-Assisted Transamidation

The C-N bond transamidation of primary amides with N,N-dimethyl enaminones has been efficiently realized by heating in the presence of trifluoromethanesulfonic acid (TfOH). The method enables the practical synthesis of valuable enamides without the use of any metal reagent. In addition, this transamidation protocol can also be expanded to the reactions of sulfonamides, and the late-stage functionalization on sulfonamide drugs such as Celecoxib and Valdecoxib has been verified. Moreover, the participation of water in assisting the transamidation process has been identified by the isotope labeling experiments using D2O, disclosing a new possibility in designing catalytic tactic to other transamidation reactions.

1,2,4-Triazines and Calcium Carbide in the Catalyst-Free Synthesis of 2,3,6-Trisubstituted Pyridines and Their D-, 13 C-, and Doubly D2 -13 C2 -Labeled Analogues

A novel synthetic approach to 2,3,6-trisubstituted pyridines, their 4,5-dideuterated derivatives, 4,5-13 C2 - and doubly-labeled D2 -13 C2 -pyridines has been developed using catalyst-free [4+2] cycloaddition of 1,2,4-triazines and in situ generated acetylene or labeled acetylene. Calcium carbide and water or deuterium oxide were used for the in situ generation of acetylene and dideuteroacetylene. Calcium carbide-13 C2 in the mixture with water or deuterium oxide was applied as 13 C2 -acetylene and D2 -13 C2 -acetylene source.

Synthesis of Tetrahydro-indolones through Rh(III)-Catalyzed [3 + 2] Annulation of Enaminones with Iodonium Ylides

An unprecedented protocol for a Rh(III)-catalyzed [3 + 2] annulation from simple and readily available enaminones and iodonium ylides has been developed. The novel strategy allows for access to a new class of structurally diverse tetrahydro-indolones with high efficiency and a broad substrate scope. In addition, this transformation represents the first example of the selective Rh(III)-catalyzed alkenyl C-H bond functionalization and annulation of enaminones. Finally, the potential applications of this protocol are demonstrated through gram-scale reaction and late-stage modification.

Rh(III)-Catalyzed [3 + 2] Annulation/Pinacol Rearrangement Reaction of Enaminones with Iodonium Ylides: Direct Synthesis of 2-Spirocyclo-pyrrol-3-ones

A novel Rh(III)-catalyzed cascade alkenyl C-H activation/[3 + 2] annulation/pinacol rearrangement reaction of enaminones with iodonium ylides has been developed. This methodology provides a new and straightforward synthetic strategy to afford highly functionalized 2-spirocyclo-pyrrol-3-ones in satisfactory yield from readily available starting materials under mild conditions. Moreover, gram-scale reactions and further derivatization experiments are implemented to demonstrate the potential utility of this developed approach.

Synthesis of 4-Alkylated 1,4-Dihydropyridines: Fe(II)-Mediated Oxidative Cascade Cyclization Reaction of Cyclic Ethers with Enaminones

Syntheses of highly functionalized 4-alkylated 1,4-dihydropyridines (1,4-DHPs) from cyclic ethers and enaminones via iron(II)-mediated oxidative free radical cascade C(sp3)-H bond functionalization/C(sp3)-O bond cleavage/cyclization reaction have been first developed. This novel synthetic strategy offers an alternative method for the construction of 1,4-DHPs by using esters as the C4 sources, as well as expands the application of ethers in heterocycle synthesis.

I2-DMSO-Mediated Transannulation of Benzo[d]isoxazol-3-amine: Direct Access to 2,4,5-Substituted Pyrimidine Derivatives

An I2-DMSO-mediated multicomponent [3+1+2] cascade annulation reaction using aryl methyl ketones, enaminones, and benzo[d]isoxazol-3-amine as substrates has been developed. This metal-free reaction involved the transannulation of benzo[d]isoxazol-3-amines with the formation of two C-N bonds and a C-C bond in one pot. Notably, a pyrimidine ring with a 1,4-dicarbonyl scaffold could efficiently transform into a pyrimido[4,5-d]pyridazine skeleton. The phenolic hydroxyl group of the target product could undergo further modification with pharmaceuticals, demonstrating the utility of this method.

One Stone, Three Birds: One-Pot Synthesis of Pyrido[3,2-a]phenoxazin-5-one Derivatives from o-Aminophenols with Triple Roles, Paraformaldehyde, and Enaminones via the Povarov Reaction

A novel multicomponent cascade cyclization reaction in one pot for the preparation of pyrido[3,2-a]phenoxazin-5-ones from simple o-aminophenols, paraformaldehyde, and enaminones has been established. It is noteworthy that o-aminophenol plays multiple roles serving as both a bis-nucleophile and an iminoquinone precursor, which can in situ generate aminophenoxazinones to undergo the Povarov reaction for the first time to yield pyrido[3,2-a]phenoxazin-5-ones with a high efficiency. Moreover, the photoluminescence of pyrido[3,2-a]phenoxazin-5-ones has polarity sensitivity and features aggregation-induced emission (AIE) characteristics, which is promising for bioimaging and theranostic applications.

Iodine-Mediated Oxidative Annulation of β,γ-Unsaturated Hydrazones in Dimethyl Sulfoxide: A Strategy to Build 1,6-Dihydropyridazines and Pyrroles

Simple, commercially available iodine was successfully employed as a highly efficient and chemoselective catalyst for the oxidative annulation of β,γ-unsaturated hydrazones to produce 1,6-dihydropyridazines under mild conditions for the first time. Interestingly, when active β,γ-unsaturated hydrazone compounds containing electron-donating groups, such as furyl, thienyl, and cycloalkyl, were used, pyrroles were obtained. A gram-scale preparation experiment and further derivatization of pyridazines demonstrated the potential applicability of our synthesis method. Experimental studies and density functional theory calculations unveiled the origin of the chemoselectivity determining the formation of different products.

Three-Component Chemo-Selective Synthesis of N-(o-Alkenylaryl) Pyrazoles by Pyrazole Annulation and Rh-Catalyzed Chemo-Selective Aryl C-H Addition Cascade

By using readily available enaminones, aryl hydrazine hydrochlorides, and alkynes as starting materials, the chemo-selective three-component synthesis of atropisomeric N-(o-alkenylaryl) pyrazoles has been efficiently accessed with rhodium catalysis. Unlike Satoh-Miura reaction leading to the alkyne-based C-H benzannulation by using prior prepared N-phenyl pyrazoles and alkynes as substrates, this three-component protocol displays unprecedented selectivity of C-H alkenylation by blocking the second round metal alkenylation with the key protonation step in the presence of acids.

Tunable vicinal, geminal diphosphorylation and C-N bond phosphorylation of enaminones toward divergent phosphorylated ketone derivatives

This paper reports the trifunctionalization reactions of tertiary enaminones in the fashion of selective gem- and vicinal diphosphorylation, leading to the tunable synthesis of α,α- and α,β-diphosphoryl ketones. In addition, the C-N bond phosphorylation with improved substrate tolerance has been achieved.

I2-Promoted gem-Diarylethene Involved Aza-Diels-Alder Reaction and Wagner-Meerwein Rearrangement: Construction of 2,3,4-Trisubstituted Pyrimido[1,2-b]indazole Skeletons

A [3 + 1 + 2] cyclization-rearrangement reaction scheme was developed to synthesize pyrimido[1,2-b]indazoles from aryl methyl ketones, 3-aminoindazoles, and gem-diarylethenes. This metal-free process proceeds via a sequential aza-Diels-Alder reaction and Wagner-Meerwein rearrangement, and a possible reaction mechanism was demonstrated based on control experiments. This method exhibits good substrate compatibility and allows simple reaction conditions. Moreover, the products display significant aggregation-induced emission characteristics after simple modifications.

Three-Component Fusion to Pyrazolo[5,1-a]isoquinolines via Rh-Catalyzed Multiple Order Transformation of Enaminones

A facile and practical method for the synthesis of fused tricyclic pyrazolo[5,1-a]isoquinolines has been realized via the reactions of enaminones, hydrazine hydrochloride, and internal alkynes. By means of Rh catalysis, the extraordinary high-order bond functionalization, including the transformation of aryl C-H, ketone C═O, and alkenyl C-N bonds in the enaminones, marks the major feature of the cascade reactions. The results disclose the individual advantage of enaminones in the design of novel and efficient synthetic methods.

Thiazole-5-carbaldehyde Synthesis by Cascade Annulation of Enaminones and KSCN with Dess-Martin Periodinane Reagent

The Dess-Martin periodinane (DMP) reagent-mediated reactions of tertiary enaminones with potassium thiocyanate for the synthesis of thiazole-5-carbaldehydes are developed. The product formation involves cascade hydroxyl thiocyanation of the C═C double bond, intramolecular hydroamination of the C≡N bond, and thiazole annulation by condensation on the ketone carbonyl site, representing novel reaction pathways in the reactions between enaminones and thiocyanate salt. DMP plays dual roles in mediating the free radical thiocyanation and inducing the unconventional selective thiazole-5-carbaldehyde formation by masking the in situ generated formyl group during the reaction process.