Annulation Of Allenoates Research Articles

Continuous Flow Spirocyclization Reactions: Towards Efficient Synthesis of Chiral Spiropenicillanates

AbstractHerein, we describe the development of a continuous flow approach to chiral spiropenicillanates with remarkable bioactive properties from 6‐alkylidenepenicillanates through phosphine‐catalyzed [3+2] annulation of allenoates or 1,3‐dipolar cycloaddition with diphenyldiazomethane. Model reactions were carried out using simple alkenes, such as methyl vinyl ketone and N‐substituted maleimides, leading to the corresponding products in excellent yields (up to 96 %). The [3+2] annulation reaction was subsequently extended to the reactivity of 6‐alkylidenepenicillanates, a more complex 2π‐component with an exocyclic carbon‐carbon double bond, allowing the synthesis of spirocyclic compounds. The 1,3‐dipolar cycloaddition reactions between 6‐alkylidenepenicillanates and diphenyldiazomethane under continuous flow conditions gave the corresponding spiro‐1‐pyrazolinepenicillanates in high yields (up to 81 %). Thermal ring contraction, via N2 extrusion, of spiro‐1‐pyrazolinepenicillanates under continuous flow conditions led to spirocyclopropanepenicillanates in quantitative yields. The continuous flow proved to be an efficient methodology for the synthesis of spiropenicillanates and represents a more sustainable approach for the larger‐scale synthesis of spiropenicillanates with relevant biological activity.

A highly diastereoselective (5+1) annulation of allenoates and pyrazolones catalyzed by CH3OK.

The first (5+1) annulation of allenoates and pyrazolones catalyzed by CH3OK has been reported. A series of spiro-pyrazolone derivatives were obtained as single diastereomers in high yields (≤95%) under mild conditions. The synthetic utility was demonstrated by a scale-up reaction and various transformations of the products. The proposed mechanism suggests that the allenoate works as a 1,5-biselectrophilic 5C synthon for the first time and controlled experiments disclose that K+ plays an important role in the diastereoselectivity-determining step through an eight-membered ring transition state. Also, this 1,5-biselectrophilic allenoate will be able to act as a 5C synthon for (5+n) annulation.

A Direct Route to Tetrahydropyridazine Derivatives via DMAP‐Catalyzed [4+2] Annulation of Allenoates with Arylazosulfones

Comprehensive SummaryHerein, a DMAP‐catalyzed [4+2] annulation of α‐substituted allenoates with arylazosulfones is reported, which affords facile access to tetrahydropyridazine derivative in synthetically useful yields. This reaction features mild conditions and good functional group tolerance. Moreover, the resultant products can be readily transformed into pyridazin‐3‐one derivatives in the presence of DDQ.

Phosphine-Catalyzed Sequential [3 + 2]/[3 + 2] Annulation between Allenoates and Arylidenemalononitriles for the Enantioselective Construction of Bicyclo[3,3,0]octenes and Cyclopenta[c]quinolinones.

A highly diastereo- and enantioselective phosphine-catalyzed sequential [3 + 2]/[3 + 2] annulation of allenoates with arylidenemalononitriles has been developed. This reaction allows for the facile construction of multifunctionalized cis-fused bicyclic[3,3,0]octene scaffolds, encompassing three consecutive stereogenic centers with one quaternary carbon center, in a one-step operation from readily available materials. The reported protocol is scalable, operates under mild reaction conditions, and creates the core structural motif of a number of natural products.

Phosphine-Catalyzed (4 + 2) Annulation of Allenoates with Benzofuran-Derived Azadienes and Subsequent Thio-Michael Addition.

A phosphine-catalyzed (4 + 2) annulation of tetrahydrobenzofuranone-derived allenoates and benzofuran-derived azadienes (BDAs) has been achieved to construct the decahydro-2H-naphtho[1,8-bc]furan derivatives, which were subsequently treated with 4-methylbenzenethiol and trimethylamine to produce thio-Michael addition products in high to excellent yields with good diastereoselectivities.

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.

Theoretical insights into phosphine‐catalyzed [4 + 2] annulation of allenoates with thiazolone‐derived alkenes

AbstractIn this article, the mechanism of [4 + 2] annulation of allenoates with thiazolone‐derived alkenes catalyzed by phosphine has been studied using density functional theory (DFT). This work adopted the two different phosphine catalysts (named as Cat1 and Cat2) to participate in the theoretical calculation. Catalyst Cat1 was used as a chiral catalyst to obtain optically active products in good yield with excellent enantioselectivity. With the use of Cat2 as the achiral catalyst, products were not enantioselective. The calculated results indicate that the CC bond formation is not only the rate‐determining step but also the stereoselectivity‐determining step. The R‐configured product is predicted as the dominant product catalyzed by Cat1, which is consistent with the experimental results. Moreover, global reaction index (GRI), natural bond orbital (NBO), and frontier molecular orbital (FMO) analyses indicate that the phosphine catalyst can enhance the nucleophilicity of reactant R1 and reduce the energy gap of the interacting HOMO and LUMO orbitals. The revealed mechanism would provide valuable clues in novel catalyst design.

Enantioselective [4+2] Annulation to the Concise Synthesis of Chiral Dihydrocarbazoles.

SummaryA highly efficient phosphine-catalyzed enantioselective [4 + 2] annulation of allenoates with 3-nitroindoles or 3-nitrobenzothiophenes has been developed. The protocol represents a unique dearomatization–aromatization process to access functionalized dihydrocarbazoles or dihydrodibenzothiophenes with high optical purity (up to 97% ee) under mild reaction conditions. The synthetic utility of the highly enantioselective [4 + 2] annulation enables a concise synthesis of analgesic agent.

Expansion of annulation of allenoates with trifluoroketones: Synthesis of trifluoromethylated dihydropyrans

The DABCO-catalyzed [2 + 2] annulation of allenoates with trifluoroketones could be expanded to [4 + 2] annulation to synthesize trifluoromethylated dihydropyrans with trifluoromethyl oxadienes as the electrophilic annulation partners.

Phosphine-Promoted Divergent Annulations of δ-Acetoxy Allenoates with α-Hydroxy-β-carbonyl Ester Derivatives: Synthesis of Tetrasubstituted Cyclopentadienes and Benzenes.

The substrate-dependent annulations of δ-acetoxy allenoates with α-hydroxy-β-carbonyl ester derivatives are reported. 2-[(Methoxycarbonyl)oxy]malonate as a C1 partner is able to undergo (1 + 4) annulations with allenoates in the presence of a catalytic amount of phosphine, affording cyclopentadienes in good yields. However, (2 + 4) annulations of allenoates with 2-(tosyloxy)-3-ketoesters are instead observed with the assistance of stoichiometrical phosphine and base, leading to tetrasubstituted benzene products. In these two reactions, δ-acetoxy allenoate serves as a 1,4-disubstituted diene synthon.

Phosphine-Promoted [4 + 3] Annulation of Allenoate with Aziridines for Synthesis of Tetrahydroazepines: Phosphine-Dependent [3 + 3] and [4 + 3] Pathways.

In this manuscript, phosphine-dependent [3 + 3] and [4 + 3] annulation reactions of allenoate with aziridines were disclosed. The alkyldiphenylphosphine-promoted [4 + 3] annulation of allenoate with aziridines has been achieved under mild conditions, providing biologically interesting functionalized tetrahydroazepines in moderate to excellent yield with moderate to excellent regioselectivity and diastereoselectivity.

Facile access to highly functionalized hydroisoquinoline derivatives via phosphine-catalyzed sequential [3+3]/[3+3] annulation.

An unprecedented sequential [3+3]/[3+3] annulation of allenoates and dienes catalyzed by phosphine has been developed, which provides novel and facile access to highly functionalized hydroisoquinoline derivatives. The reaction features a wide reaction scope and mild reaction conditions. δ-sulfonamido-allenoates, acting as a five-atom unit, represent a new synthon in the reactions of allenoates.

Toward a Predictive Understanding of Phosphine-Catalyzed [3 + 2] Annulation of Allenoates with Acrylate or Imine.

Both theoretical and experimental studies were performed to explore the mechanism, regioselectivity, and enantioselectivity of phosphine-catalyzed [3 + 2] annulation between allenoates and acrylate or imine. Using density functional theory computations, we predicted that the enantioselective determining step is the nucleophilic addition of acrylate or imine to the catalyst-activated allenoate. In the key step, we proposed two hydrogen bonding interaction models (intermolecular H-bond model and intramolecular H-bond model). For acrylate substrates, the reaction proceeds via the intramolecular H-bond model and the strong noncovalent interactions between the 2-naphthyl ester moiety lead to the re-face attack pathway being more favorable. For imine substrates, the intermolecular H-bond model operates. In the annulation process, the bulky n-propyl oriented toward a crowded, sterically demanding environment plays a significant role in asymmetric induction. The theoretical calculation results agreed with experimental observations, and these results provide valuable insight into catalyst design and understanding of mechanisms of related reactions.

Mechanisms of phosphine‐catalyzed [4 + 3] annulation of allenoates with C, N‐cyclic azomethine imines: A DFT investigation

AbstractIn this article, mechanisms of phosphine‐catalyzed [4 + 3] annulation of allenoates with C, N‐cyclic azomethine imines have been investigated using density functional theory. The catalytic cycle for the title reaction consists of five steps. Namely, the first step is the nucleophilic addition of phosphine catalyst, the second one is the CC bond formation, the third one is the proton transfer process, and the next one is the ring‐closure process, the last one is dissociation of the catalyst and the product generation. The calculated results indicate that the nucleophilic addition of phosphine catalyst is rate‐determining. With the use of Cat as the chiral catalyst, optically active products were obtained in good yields with excellent enantioselectivities while the CC bond formation is stereoselectivity‐determining. Furthermore, the theoretically predicted the main product is SS configuration, which is in good agreement with the experimental results. The special role of the catalysts and origin of stereoselectivity was also identified by NBO, GRI, and FMO analyses. This work might be helpful for understanding the significant roles of phosphine catalyst and thus provide valuable insights on the rational design of potential catalysts for this kind of reactions.

Planar chiral [2.2]paracyclophane-based phosphine-phenols: use in enantioselective [3 + 2] annulations of allenoates and N-tosylimines.

Planar chiral [2.2]paracyclophane-based phosphine-phenol catalysts, which have a benzene ring spacer inserted between the pseudo-ortho-substituted [2.2]paracyclophanol skeleton and the diarylphosphino group, are highly suitable for enantioselective [3 + 2] annulations of allenoates and N-tosylimines. These catalysts can be tuned by changing the substituent on the benzene rings of the diarylphosphino group. The observed enantioselectivity of 92% is the highest reported to date for phosphine-catalyzed annulations of unsubstituted allenic esters and N-tosylaldimines.

Phosphine-Catalyzed [4 + 2] Annulation of Allenoate with Sulfamate-Derived Cyclic Imines: A Reaction Mode Involving γ'-Carbon of α-Substituted Allenoate.

A phosphine-catalyzed [4 + 2] cycloaddition of cyclic α-substituted allenoates with sulfamate-derived cyclic imines has been reported. Using dibenzylphenylphosphine as the nucleophilic catalyst, the reaction worked efficiently to yield various fused multicyclic heterocyclic compounds in high yields with excellent diastereoselectivities. It undergoes a new reaction mode involving γ'-carbon of α-substituted allenoate.

ChemInform Abstract: Phosphine‐Catalyzed [2 + 4] Annulation of Allenoates with Thiazolone‐Derived Alkenes: Synthesis of Functionalized 6,7‐Dihydro‐5H‐pyrano[2,3‐d]thiazoles.

Phosphine-catalyzed [2 + 4] annulation of allenoates with thiazolone-derived alkenes has been achieved under mild conditions, giving biologically important 6,7-dihydro-5H-pyrano[2,3-d]thiazole derivatives in high to excellent yields. With the use of Kwon’s phosphine as the chiral catalyst, optically active products were obtained in good yields with excellent enantioselectivities.

Phosphine-Catalyzed Enantioselective [4 + 3] Annulation of Allenoates with C,N-Cyclic Azomethine Imines: Synthesis of Quinazoline-Based Tricyclic Heterocycles.

With the use of a commercially available chiral phosphine as the catalyst, the first catalytic enantioselective [4 + 3] annulation of allenoates with C,N-cyclic azomethine imines is developed. The reaction works efficiently under mild reaction conditions to afford seven-membered ring-fused quinazoline-based tricyclic heterocycles in high yields with good to excellent diastereo- and enantioselectivities.

Phosphine-Catalyzed Domino Annulations of Allenoates and Ketimines

Phosphine-Catalyzed Domino Annulations of Allenoates and Ketimines

Phosphine-Catalyzed [2 + 4] Annulation of Allenoates with Thiazolone-Derived Alkenes: Synthesis of Functionalized 6,7-Dihydro-5H-pyrano[2,3-d]thiazoles.

Phosphine-catalyzed [2 + 4] annulation of allenoates with thiazolone-derived alkenes has been achieved under mild conditions, giving biologically important 6,7-dihydro-5H-pyrano[2,3-d]thiazole derivatives in high to excellent yields. With the use of Kwon's phosphine as the chiral catalyst, optically active products were obtained in good yields with excellent enantioselectivities.