Vinylogous Aldol Reaction Research Articles

Enantioselective vinylogous aldol reaction between β,γ-unsaturated amides and isatins

A highly enantioselective vinylogous aldol reaction between β,γ-unsaturated amides and isatins has been developed to provide chiral multifunctional 3-hydroxy-2-oxindoles.

Synthesis of the bicyclic butenolide core of pallamolide A: a biomimetic approach.

Pallamolide A is a 7,8-seco-labdane terpenoid possessing a unique bicyclo[2.2.2]octane core and a spiro-butenolide moiety. A biomimetic synthesis of the bicyclic butenolide core over 10 steps is reported, featuring an unexpected autoxidation ring opening, and a vinylogous Mukaiyama aldol reaction which was spontaneously followed by an unusual intramolecular vinylogous aldol reaction to assemble the spiro-butenolide moiety and bicyclic core of pallamolide A.

Lewis Base-Catalyzed Intramolecular Vinylogous Aldol Reaction and Chemoselective Syntheses of 3-Hydroxy-2,3-Disubstituted Dihydrobenzofurans and Indolines.

A Lewis base-catalyzed intramolecular vinylogous aldol reaction of o-(allyloxy)phenyl ketoesters or o-(allylamino)phenyl ketoesters has been developed. This reaction provides ready access to 3-hydroxy-2,3-disubstituted dihydrobenzofurans and indolines in high yields with excellent chemoselectivity and diastereoselectivity. An acid-promoted dehydration of such products further extends the utility of the reaction to the synthesis of 2-alkenyl benzofurans and indoles.

Selective Vinylogous Aldol Reactions of β‐Methyl‐Substituted Cyclic Enones with Isatins Catalyzed by DBU and Pyrrolidine to Afford 3‐Substituted 3‐Hydroxyoxindoles

AbstractThe development of regioselective aldol reactions of β‐methyl‐substituted cyclic enone derivatives with isatins to afford the aldol products with the bond formation at the methyl group of the β‐methyl‐substituted cyclic enone derivatives is described. Catalyst systems composed of DBU and pyrrolidine with DMSO were identified that resulted in the aldol reactions with almost perfect regioselectivities. DBU, pyrrolidine, and DMSO were all required to selectively afford the γ‐position‐reacted aldol products. With the use of this method, the scope of the 3‐substituted 3‐hydroxyoxindole derivatives that can be concisely synthesized was expanded.

Photochemical diastereoselective synthesis and spectral characterization of (E)-3-(2-benzoylstyryl)-4H-chromen-4-ones

An efficient, concise, and green photochemical vinylogous aldol reaction for the diastereoselective synthesis of novel trans-3-(2-benzoylstyryl)-4H-chromen-4-ones starting from readily available methylbenzophenone and 3-formylchromone in the absence of any bases, metals, or other catalysts is described. The products could be obtained under UV LED (365 nm) irradiation at room temperature in 9 h with perfect diastereoselectivity. To discuss the special patterns of alkene protons, to identify its trans-conformation and verify the two trans-alkene protons (β-H and γ-H), NMR spectra analysis (1D-NMR and 2D-NMR) was conducted in details by the chemical shifts, couplings and correlations. Single crystal X-ray analysis confirmed the trans-conformation and all the compounds were unequivocally confirmed by NMR, HRMS and XRD analysis. XRD analysis of 3a further aids to disclose the reason why the alkene moiety presented a better planarity than that of benzophenone moiety of the title compounds.

Biogenesis-Inspired Synthesis of Penicillitone

AbstractThe biogenesis-inspired synthesis of the structurally unique 15(14→11)abeo-steroid penicillitone starting from commercially available ergosterol is reported. Key to the strategy is an intramolecular vinylogous aldol reaction of a 14,15-secoergostane obtained from the previously reported 14,15-secosteroid platform. Since a similar intermediate has been employed to access the strophasterol class of natural products, this work points at a possible biosynthetic connection between penicillitone and the strophasterols.

Synthesis and Evaluation of N-Diaminophosphoryl Aminothioureas as Bifunctional Catalysts for Vinylogous Aldol Reactions of Isatins and 2(3H)-Furanones.

The organocatalytic asymmetric direct vinylogous aldol reaction of N-methylisatins 1 and γ-butenolides 2 to provide 3-hydroxy-2-oxindole derivatives 3 was investigated. A series of N-diaminophosphoryl aminothiourea catalysts 4 was synthesized, and their utility for the stereoselective formation of 3 was examined.

A formal synthesis of (-)-erinacine B enabled by asymmetric organocatalysis.

A unified strategy for accessing the core structure of cyathane diterpenoids has been developed, enabling the formal synthesis of (-)-erinacine B. The key feature includes an organocatalyzed asymmetric intramolecular vinylogous aldol reaction for convergently building up the 5-6-6 tricyclic ring system. This strategy also highlights a hydroxyl-directed cyclopropanation/ring opening sequence to stereoselectively set up 1,4-anti and -cis angular-methyl quaternary carbon centers.

Convergent Synthesis of Enantioenriched ortho-Fused Tricyclic Diketones via Catalytic Asymmetric Intramolecular Vinylogous Aldol Condensation.

Herein, we describe a catalytic asymmetric intramolecular vinylogous aldol reaction by taking advantage of dual organocatalysts, which enables convergent synthesis of ortho-fused tricyclic diketones in excellent enantioselectivities and diastereoselectivities. Noteworthy is that the reaction stereoselectively forges three consecutive stereogenic carbon centers including a quaternary one. Density functional theory calculations reveal that the enantioselectivity was facilitated by a transannular hydrogen bonding between the protonated quinuclidine moiety of the chiral aminocatalyst and the diketone fragment of the substrate.

Highly enantioselective vinylogous aldol reaction of dioxinone-derived silyl diene by combined Lewis acid catalyst

Highly enantioselective vinylogous aldol reaction of dioxinone-derived silyl diene by combined Lewis acid catalyst

Exploring the Synthetic Potential of γ-Lactam Derivatives Obtained from a Multicomponent Reaction-Applications as Antiproliferative Agents.

A study on the reactivity of 3-amino α,β-unsaturated γ-lactam derivatives obtained from a multicomponent reaction is presented. Key features of the substrates are the presence of an endocyclic α,β-unsaturated amide moiety and an enamine functionality. Following different synthetic protocols, the functionalization at three different positions of the lactam core is achieved. In the presence of a soft base, under thermodynamic conditions, the functionalization at C-4 takes place where the substrates behave as enamines, while the use of a strong base, under kinetic conditions, leads to the formation of C-5-functionalized γ-lactams, in the presence of ethyl glyoxalate, through a highly diastereoselective vinylogous aldol reaction. Moreover, the nucleophilic addition of organometallic species allows the functionalization at C-3, through the imine tautomer, affording γ-lactams bearing tetrasubstituted stereocenters, where the substrates act as imine electrophiles. Taking into account the advantage of the presence of a chiral stereocenter in C-5 substituted γ-lactams, further diastereoselective transformations are also explored, leading to novel bicyclic substrates holding a fused γ and δ-lactam skeleton. Remarkably, an example of a highly stereoselective formal [3+3] cycloaddition reaction of chiral γ-lactam substrates is reported for the synthesis of 1,4-dihidropyridines, where a non-covalent attractive interaction of a carbonyl group with an electron-deficient arene seems to drive the stereoselectivity of the reaction to the exclusive formation of the cis isomer. In order to unambiguously determine the substitution pattern resulting from the diverse reactions, an extensive characterization of the substrates is detailed through 2D NMR and/or X-ray experiments. Likewise, applications of the substrates as antiproliferative agents against lung and ovarian cancer cells are also described.

Catalytic Diastereo- and Enantioselective Synthesis of Tertiary Trifluoromethyl Carbinols through a Vinylogous Aldol Reaction of Alkylidenepyrazolones with Trifluoromethyl Ketones.

A diastereo- and enantioselective organocatalytic aldol reaction between alkylidenepyrazolones and trifluoromethyl ketones leading to chiral tertiary alcohols bearing a trifluoromethyl group is presented. The methodology is based on the use of a bifunctional organocatalyst in order to activate the γ-hydrogen atoms of the alkylidenepyrazolone nucleophile and the carbonyl group of the trifluoromethylarylketone providing highly functionalized trifluoromethyl alcohols with moderate yields, excellent diastereoselectivity, and moderate to good enantioselectivity. Experiments monitoring the conversion by 1H NMR and the enantiomeric excess by HPLC with the reaction time showed that full conversion of the starting materials is not achieved and that the enantiomeric excess decreases upon extended times, probably due to the reversibility of the reaction.

UV light-driven asymmetric vinylogous aldol reaction of isatins with 2-alkylbenzophenones and enantioselective synthesis of 3-hydroxyoxindoles

A UV light-driven enantioselective synthesis of 3-hydroxyoxindoles is reported for the first time.

Phosphine-Catalyzed Intramolecular Vinylogous Aldol Reaction of α-Substituted Enones.

We demonstrate the first phosphine-catalyzed intramolecular vinylogous aldol reaction (IVAR) of α-substituted enones. This strategy provides access to various pentannulated (hetero)arenes and dibenzocycloheptanones incorporated with two contiguous stereocenters, one of which is an all-carbon quaternary center. The scope of this work is further broadened through elaborations of the IVAR adducts to (i) benzannulated nine-membered carbocyclic systems, (ii) interesting classes of 1,3-dienes, 1,3,5-trienes, and 1-yn-3,5-dienes, and (iii) the analogs of echinolactone D and russujaponol F.

Development of Green Asymmetric Organocatalytic Synthesis

Organocatalysts, which are less toxic than metal catalysis, as well as inexpensive, environmentally benign, and stable against moisture and oxygen compared to metal-based catalysts, have received considerable attention for being efficient and clean catalysts. With respect to green chemistry, the development of organocatalysis is a significant research subject for a sustainable society. This article reviews studies on the development of novel organocatalysts and the reactions achieved from using them. Focusing on the push-pull ethylene moiety, in which two electron-withdrawing groups (EWGs) were introduced, we proposed that the vinylogous amide proton (N-H) will lead to the design of organocatalysts. We have developed the diaminomethylenemalononitrile (DMM) organocatalysts, which are push-pull ethylenes having two cyano groups as EWGs, and proved that they are effective for highly stereoselective hydrophosphonylation with aldehydes. The catalytic ability of the DMM organocatalyst was demonstrated in the development of the first asymmetric hydrophosphonylation of ketones using organocatalysts. The DMM organocatalyst can be applied to the selective 1,4-addition asymmetric hydrophosphonylation of enones. In addition, we designed and synthesized novel organocatalysts bearing squaramide-sulfonamide motif as multiple hydrogen bond donors. Squaramide-sulfonamide organocatalysts efficiently catalyzed the asymmetric direct vinylogous aldol reactions of furan-2(5H)-one with aldehydes. Successively, we achieved the synthesis of γ,γ-disubstituted-δ-hydroxy-γ-butenolide via asymmetric direct vinylogous aldol reaction of furanone derivatives using the squaramide-sulfonamide organocatalysts.

Optimization of Two Steps in Scale-Up Synthesis of Nannocystin A

We have accomplished a 10-step (longest linear) total synthesis of nannocystin A on a four hundred milligram scale. The previously reported Kobayashi vinylogous Mukaiyama aldol reaction to connect C4 and C5 was unreproducible during the scaling up process. A more convenient and cost-efficient Keck asymmetric vinylogous aldol reaction was employed to improve this transformation.

Copper-Catalyzed Enantioselective Vinylogous Aldol Reaction of Allylazaarenes

Copper-Catalyzed Enantioselective Vinylogous Aldol Reaction of Allylazaarenes

Catalytic enantioselective synthesis of chiral 4-hydroxy 4′-substituted pyrazolones by the vinylogous aldol reaction of pyrazole-4,5-diones with 3-alkylidene-2-oxindoles

Here, a bifunctional quinine-derived benzamide catalyzed direct enantioselective vinylogous aldol reaction between 3-alkylidene-2-oxindoles and pyrazole-4,5-diones has been developed.

Enantioselective vinylogous aldol reaction of acylphosphonates with 3-alkylidene oxindoles.

A simple strategy for yielding chiral tertiary α-hydroxy phosphonates that integrates two highly biologically relevant scaffolds namely 3-alkylidene-2-oxindoles and phosphonates has been described. The hydrogen bonding ability of the bifunctional thiourea catalyst allows simultaneous dual activation of a vinylogous oxindole nucleophile and an acylphosphonate electrophile, affording hydroxyphosphonato-3-alkylidene-2-oxindoles as aldol adducts in high yields (up to 92%) with excellent stereocontrol (up to 99% ee).

Stereocontrolled Synthesis of (-)-Bactobolin A.

A stereoselective synthesis of the ribosome-binding antitumor antibiotic (-)-bactobolin A is reported. The presented approach makes effective use of (-)-quinic acid as a chiral pool starting material and substrate stereocontrol to establish the five contiguous stereocenters of (-)-bactobolin A. The key steps of the synthesis include a stereoselective vinylogous aldol reaction to introduce the unusual dichloromethyl substituent, a completely diastereoselective rhodium(II)-catalyzed C-H amination reaction to set the configuration of the axial amine, and an intramolecular alkoxycarbonylation to build the bicyclic lactone framework. The developed synthetic route was used to prepare 90 mg of (-)-bactobolin A trifluoroacetate in 10% overall yield.