Synthesis of Pyrimidopyrrolopyridazines via a Tandem Reaction of Heterocyclic Ketene Aminals with 1,2-Diaza-1,3-dienes

Radical Cascade Reaction of Heterocyclic Ketene Aminals with Thiocyanates Promoted by Visible Light: Synthesis of Functionalized Fused 2-Iminothiazolines

Herein, a visible-light-promoted radical cascade cyclization of heterocyclic ketene aminals (HKAs) and thiocyanates was developed to access functionalized fused 2-iminothiazolines. This novel cascade reaction can be realized under only visible-light irradiation without the help of external photocatalysts, oxidants, and additives. These multicomponent cascade reactions demonstrate excellent selectivity for the Z-isomers and ensure the formation of the products only in their isomeric form. Preliminary mechanism investigations demonstrated that HKAs and thiocyanates can form electron donor-acceptor complexes for harvesting the energy of visible light to activate substrates and generate reactive radicals. This protocol can be used for synthesizing various natural-like products such as fused 2-iminothiazolines. This approach demonstrates multiple advantages such as commercially available substrates, convenient operation, environmentally friendly, mild conditions, and an efficient multicomponent reaction (2A + B).

Hydroxyl-Directed Rh(III)-Catalyzed C-H Functionalization: Access to Benzo[de]chromenes

A cascade oxidative annulation reaction of heterocyclic ketene aminals (HKAs) with internal alkynes catalyzed by [Cp*RhCl₂]₂ and oxidized by Cu(OAc)₂·H₂O was developed to efficiently synthesize highly functionalized benzo[de]chromene derivatives in good to excellent yields. The reaction proceeded by the sequential cleavage of C(sp²)-H/O-H and C(sp²)-H/C(sp²)-H bonds. These multicomponent cascade reactions were highly regioselective. In addition, all of the benzo[de]chromene products exhibited intense fluorescence emission in the solid state, and they demonstrated concentration-dependent quenching in the presence of Fe³⁺, indicating that these compounds could be used in the recognition of Fe³⁺.

Catalytic [2,3]-sigmatropic rearrangement of sulfonium ylides derived from azoalkenes: non-carbenoid Doyle-Kirmse reaction

The Sc(III)-catalyzed [2,3]-sigmatropic rearrangement of sulfonium ylides derived from azoalkenes has been established. Owing to the absence of a carbenoid intermediate, this protocol represents the first non-carbenoid variant of the Doyle-Kirmse reaction. Under mild conditions, a variety of tertiary thioethers have been readily prepared in good to excellent yields.

Multicomponent Cascade Reaction of 3-Formylchromones: Highly Selective Synthesis of Functionalized 9-Azabicyclo[3.3.1]nonane Derivatives

A novel protocol for the preparation of functionalized 9-azabicyclo[3.3.1]nonane (ABCN) derivatives from 3-formylchromones, enaminones, and heterocyclic ketene aminals (HKAs) through an unprecedented cascade reaction has been developed by simply refluxing the mixture of the substrates 1-3. As a result, a series of ABCNs were produced through a very complex cascade reaction. This protocol can be used in the synthesis of ABCNs that are suitable for combinatorial and parallel syntheses of ABCN natural-like products in a one-pot reaction.

Substrate-Tuned Domino Annulation for Selective Synthesis of Poly-substituted Benzo[f]imidazo[2,1-a][2,7]naphthyridines and 3-Azaheterocyclic Substituted 2-Arylquinolines

A domino annulation/oxidation of heterocyclic ketene aminals (HKAs) and 2-aminochalcones has been developed for the selective synthesis of poly-substituted benzo[f]imidazo[2,1-a][2,7]naphthyridines and 3-azaheterocyclic substituted 2-arylquinolines. These reactions proceed well under mild conditions without any additives. Plausible mechanisms for such a polycyclic ring system assembly were also proposed. Moreover, benzo[f]imidazo[2,1-a][2,7]naphthyridine 3g displayed a fluorescence effect, demonstrating the potential applications in organic optical materials.

Cascade reaction of isatins with nitro-substituted enamines: highly selective synthesis of functionalized (Z)-3-(1-(arylamino)-2-oxoarylidene)indolin-2-ones

A novel protocol for the construction of functionalized (Z)-3-(1(-arylamino)-2-oxoarylidene)indolin-2-ones (AOIDOs) from isatins 1 with nitro-substituted enamines 2via an unprecedented cascade reaction catalyzed by sulfamic acid is developed.