Synthesis of Isoxazol-5(2H)-one Derivatives via (tBuO)2Mg Promoted [3 + 2] Annulations of δ-Acetoxy Allenoates with Hydroxylamine.

Herein, an efficient (tBuO)2Mg promoted [3 + 2] annulation of δ-acetoxy allenoates with N-benzylhydroxylamine has been developed. This method provides a concise and facile protocol to synthesize vinylated isoxazol-5(2H)-one derivatives stereospecifically in a broad substrate scope with high efficiency (31 examples, up to 87% yield).

NHC-catalyzed formal [3 + 3] annulations of δ-acetoxy allenoates for the synthesis of 4H-pyran derivatives.

Herein, an N-heterocyclic carbene (NHC) catalyzed formal [3 + 3] annulation of δ-acetoxy allenoates with 1C,3O-bisnucleophiles for the construction of 4H-(fused)pyrans has been developed. This protocol provides a facile method to synthesize highly functionalized 4H-pyrans and has a broad substrate scope (30 examples, up to 77% yield).

NHC-Catalyzed [2 + 4] Annulation of Alkynyl Ester with Chalcone.

An NHC-catalyzed [2 + 4] cyclization of alkynyl ester with α,ß-unsaturated ketone to form a pyran scaffold was developed successfully. The cheap and easily available starting materials, mild reaction conditions, moderate to excellent yields, and high atom economy make this strategy attractive for the syntheses of highly substituted 4H-pyran derivatives.

NHC-catalyzed [4 + 2] annulations of allenoates and 2,3-dioxopyrrolidine derivatives.

A facile NHC-catalyzed [2 + 4] annulation of allenoates with 2,3-dioxypyrrolidine derivatives was discovered, which paved a new avenue for the construction of highly substituted pyranopyrrole with moderate to good yields, high atom economy and mild reaction conditions.

Base-promoted regiodivergent allylation of N-acylhydrazones with Morita-Baylis-Hillman carbonates by tuning the catalyst.

A regiodivergent allylation of N-acylhydrazones with Morita-Baylis-Hillman (MBH) carbonates has been developed, providing α- or γ-allylated products in excellent yields by using different catalysts. The nature of the base catalyst plays a pivotal role in controlling the reaction pathway, allowing regiospecific access to diverse allylic substituted target compounds from identical substrates.

An NHC-catalyzed, stereoselective α-functionalization of α,ß-unsaturated carboxylic acids through in situ activation.

An N-heterocyclic carbene (NHC)-catalyzed α-functionalization of the in situ activated α,ß-unsaturated carboxylic acids bearing γ-H was realized through formal [4 + 2] annulations with o-quinone methides, which paved a new avenue for the assembly and modification of the dihydrocoumarin scaffold in good yields with excellent diastereo- and enantioselectivities.

NHC-Catalyzed Aldol-Like Reactions of Allenoates with Isatins: Regiospecific Syntheses of γ-Functionalized Allenoates.

An N-heterocyclic carbene (NHC) catalyzed γ-specific aldol-like reaction between allenoates and isatins has been achieved under mild conditions, giving trisubstituted allene derivatives bearing isatin moiety in moderate to good yields with high diastereoselectivity and excellent atom efficiency. The DFT computations indicated that the formation of the γ-adduct was more energetically favorable than that of the α-adduct. The result reported herein opens a new route for NHC-promoted allenoate-involved reaction.

An enantioselective assembly of naphthopyran via NHC-catalyzed [3 + 3] annulation of bromoenal with ß-tetralone.

An asymmetric assembly of naphthopyran was realized via the N-heterocyclic carbene (NHC)-catalyzed formal [3 + 3] annulation of bromoenal and ß-tetralone. The key advantages of this protocol include ready availability of starting materials, mild reaction conditions, good yields and excellent enantioselectivities.

NHC-Catalyzed Hetero-Diels-Alder Reaction of Allenoate with Chalcone: Synthesis of Polysubstituted Pyranyl Carboxylate.

An NHC-catalyzed hetero-Diels-Alder and isomerization process of chalcones with allenoates was discovered, which furnished highly functionalized multisubstituted pyranyl carboxylates successfully. This method features a convergent assembly, mild reaction conditions, moderate to good yields, and high atom economy.

NHC-catalyzed regiodivergent syntheses of difunctionalized 3-pyrazolidinones from α-bromoenal and monosubstituted hydrazine.

A formal [3 + 2] annulation of α-bromoenal with monosubstituted hydrazine could give 1,5 or 2,5-difunctionalized 3-pyrazolidinone regiodivergently by tuning the structure of the N-Heterocyclic Carbene (NHC) catalyst. Moderate to high yields, mild reaction conditions, good regioselectivity and potential biological significance of the final product have made this protocol attractive for the assembly of 3-pyrazolidinone.

N-Heterocyclic Carbene-Catalyzed [4 + 2] Cyclization of Saturated Carboxylic Acid with o-Quinone Methides through in Situ Activation: Enantioselective Synthesis of Dihydrocoumarins.

An N-heterocyclic carbene (NHC)-catalyzed formal [4 + 2] synthesis of dihydrocoumarins was realized from saturated carboxylic acids and o-quinone methides via an in situ activation strategy. This protocol results in excellent diastereoselectivity and enantioselectivity and good yields and uses readily available and inexpensive starting materials.

NHC-catalyzed [4 + 2] annulation of 2-bromo-2-enals with acylhydrazones: enantioselective synthesis of δ-lactams.

An asymmetric assembly of δ-lactams was realized via the NHC-catalyzed formal [4 + 2] annulation of acylhydrazones and 2-bromo-2-enals bearing γ-H. The advantages of this protocol include high enantioselectivity, good yields, mild reaction conditions and potential biological significance of the final products.

N-Heterocyclic carbene-triggered transition-metal-free synthesis of 2,3-disubstituted benzofuran derivatives.

An NHC-triggered, transition-metal-free strategy for the efficient synthesis of 2,3-disubstituted benzofuran derivatives in moderate to excellent yields from aryl or alkyl aldehydes and o-quinone methides has been developed. This method features mild reaction conditions, operational simplicity, broad substrate scope and convergent assembly.

An Enantioselective Assembly of Dihydropyranones through an NHC/LiCl-Mediated in situ Activation of α,ß-Unsaturated Carboxylic Acids.

A straightforward N-heterocyclic carbene (NHC)/LiCl-mediated synthesis of dihydropyranones from α,ß-unsaturated carboxylic acids and 1,3-dicarbonyl compounds was realized through the in situ activation strategy. The key advantages of this protocol include ready availability and high stability of starting materials, good yields, and excellent enantioselectivity.

A facile one-pot synthesis of 2,3-diarylated benzo[b]furans via relay NHC and palladium catalysis.

An efficient one-pot synthesis of 2,3-diarylated benzo[b]furans was realized through the relay catalysis of N-Heterocyclic Carbene (NHC) and palladium from substituted 2'-bromodiphenylbromomethanes and aryl aldehydes. The easy availability of the starting materials, good compatibility of catalysts, convergent assembly and concomitant modification of the target scaffold, and potential utilization value of the products make this strategy attractive in organic synthesis.

N-Heterocyclic carbene-catalyzed [4 + 2] cyclization of α,ß-unsaturated carboxylic acids bearing γ-H with isatins: an enantioselective synthesis of spirocyclic oxindole-dihydropyranones.

An NHC-catalyzed asymmetric [4 + 2] annulation of isatins and α,ß-unsaturated carboxylic acids bearing γ-H gave spirocyclic oxindole-dihydropyranones successfully via an in situ activation strategy. This protocol featured easy availability of raw materials, good yields and excellent enantioselectivities (up to 99% ee).

An N-Heterocyclic Carbene-Catalyzed Oxidative γ-Aminoalkylation of Saturated Carboxylic Acids through in Situ Activation Strategy: Access to δ-Lactam.

An N-Heterocyclic Carbene (NHC)-catalyzed oxidative formal [4 + 2] annulation of acylhydrazones with saturated carboxylic acids bearing γ-H to assemble δ-lactams featuring a chiral carbon stereogenic center was developed through an in situ activation strategy. The ready availability of the starting materials, excellent enantioselectivity, facile assembly, high yields, and potential biological significance of the final products make this protocol an attractive alternative for the construction of the pyridinone scaffold.

An efficient synthesis of [1,3]dioxolo[4,5-g]thieno[3,4-b]quinolin-8(5H)-ones as novel thiazapodophyllotoxin analogues with potential anticancer activity.

A catalyst-free synthesis of 6,9-dihydro-[1,3]dioxolo[4,5-g]thieno[3,4-b]quinolin-8(5H)-ones as novel analogues of podophyllotoxins was developed by a three-component reaction of aldehydes, ethyl 2,4-dioxotetrahydrothiophene-3-carboxylate and 3,4-(methylenedioxy)aniline. This methodology not only provides new chemical library for the screening of anticancer activity, but also features excellent isolated yields, short reaction time, simple work up procedure and little environmental impact.

Enantioselective assembly of spirocyclic oxindole-dihydropyranones through NHC-catalyzed cascade reaction of isatins with N-hydroxybenzotriazole esters of α,ß-unsaturated carboxylic acid.

An NHC-catalyzed formal [4 + 2] reaction of isatins with N-hydroxybenzotriazole ester of α,ß-unsaturated carboxylic acids bearing γ-H to construct spirocyclic oxindole-dihydropyranones featuring a chiral tetrasubstituted carbon stereogenic center was developed. The high enantioselectivity, the ready availability of the raw materials, the facile assembly, and the potential biological significance of the final products make this protocol an attractive alternative for the synthesis of spirocyclic heterocycles.

An NHC-catalyzed in situ activation strategy to ß-functionalize saturated carboxylic acid: an enantioselective formal [3+2] annulation for spirocyclic oxindolo-γ-butyrolactones.

An in situ NHC-catalyzed activation strategy to ß-functionalize saturated carboxylic acid was developed. This asymmetric formal [3+2] annulation could deliver spirocyclic oxindolo-γ-butyrolactones from saturated carboxylic acid and isatin in good yields with high to excellent enantioselectivities. The easy availability of the starting materials, direct installation of functional units at unreactive carbon atom and the convergent assembly make this protocol attractive in the field of organic synthesis.