Recent advances in transition-metal-free arylation reactions involving hypervalent iodine salts

• Ritu Mamgain,
• Kokila Sakthivel and
• Fateh V. Singh

Beilstein J. Org. Chem. 2024, 20, 2891–2920, doi:10.3762/bjoc.20.243

• base-mediated deprotonation of substrates 86 produces the corresponding ester enolate. This enolate undergoes a retro-Michael reaction, generating sulfenate anion A. The sulfenate anion A then nucleophilically attacks the diaryliodonium salts 16, forming hypervalent iodine intermediates B. Finally

Diastereoselective synthesis of highly substituted cyclohexanones and tetrahydrochromene-4-ones via conjugate addition of curcumins to arylidenemalonates

• Deepa Nair,
• Abhishek Tiwari,
• Banamali Laha and
• Irishi N. N. Namboothiri

Beilstein J. Org. Chem. 2024, 20, 2016–2023, doi:10.3762/bjoc.20.177

• double Michael adduct 3n in 56% yield (Table 2, entry 14). A plausible mechanism for the cascade double and triple Michael reactions is shown in Scheme 2. At first, the enolate I of curcumin 1 adds to arylidenemalonate 2 in a Michael fashion resulting enolate II. The ester enolate II might remain in

Synthesis and late stage modifications of Cyl derivatives

• Phil Servatius and
• Uli Kazmaier

Beilstein J. Org. Chem. 2022, 18, 174–181, doi:10.3762/bjoc.18.19

• usual conditions of an ester enolate Claisen rearrangement with zinc chloride as chelating metal gave the rearranged product in only 33% yield and a diastereomeric ratio of 93:7 (Table 1, entry 1). The reaction was kept at −45 °C overnight to suppress potential epimerization of the peptide. Generally

• , entry 1). Since the reaction seemed to stop after 30–40% conversion, it was speculated that the ester enolate chelate complex formation was incomplete due to consumption of the base. For instance, deprotonation of tyrosine residues in benzyl position has been observed previously in the derivatization of

• inhibitors with different zinc-binding motifs. Planned syntheses of Cyl-1 derivatives. Cyl-1 derivatives via peptide Claisen rearrangement. Synthesis of tetrapeptide allyl esters 8. Synthesis and late stage modifications of Cyl derivatives. Ester enolate Claisen rearrangements of tetrapeptide allyl esters 8

Microwave-assisted multicomponent reactions in heterocyclic chemistry and mechanistic aspects

• Shivani Gulati,
• Stephy Elza John and
• Nagula Shankaraiah

Beilstein J. Org. Chem. 2021, 17, 819–865, doi:10.3762/bjoc.17.71

• . The postulated mechanism indicates the formation of acylimine A from the lanthanum oxide-catalyzed reaction of aldehyde and 77. Further, addition of acyclic 1,3-diketone ester enolate to acylamine A form B which upon subsequent cyclization and dehydration resulted in the formation of desired products

Why do thioureas and squaramides slow down the Ireland–Claisen rearrangement?

• Dominika Krištofíková,
• Juraj Filo,
• Mária Mečiarová and
• Radovan Šebesta

Beilstein J. Org. Chem. 2019, 15, 2948–2957, doi:10.3762/bjoc.15.290

• -controlled Ireland–Claisen rearrangement of O-protected allylic glycolate esters proceeded with moderate yields and diastereoselectivities of up to 20:1 [25]. An asymmetric ester-enolate-Claisen rearrangement was achieved by using aluminum-chelate-bridged enolates and proceeded with high yields and

• , we studied the Ireland–Claisen rearrangement of ester 1c using various tertiary amines as bases. The ester enolate was trapped with Me3SiOTf at −60 °C and allowing the reaction to proceed at room temperature for 24 h. The best yields of acid 3c were achieved with triethylamine (74%) and N-cyclohexyl

Alkylation of lithiated dimethyl tartrate acetonide with unactivated alkyl halides and application to an asymmetric synthesis of the 2,8-dioxabicyclo[3.2.1]octane core of squalestatins/zaragozic acids

• Herman O. Sintim,
• Hamad H. Al Mamari,
• Hasanain A. A. Almohseni,
• Younes Fegheh-Hassanpour and
• David M. Hodgson

Beilstein J. Org. Chem. 2019, 15, 1194–1202, doi:10.3762/bjoc.15.116

• notable in showing that the intermediate ester enolate 14 possessed sufficient stability not to undergo significant β-elimination under conditions of its generation and its alkylation: slow addition of pre-cooled LDA (−70 °C) to a mixture of the acetonide and electrophile in THF/HMPA at −78 °C, followed

• pseudoaxial methyl of the gem-dimethyl group [18][24]; it was proposed that the axial methyl group directed electrophile incorporation away from itself (Scheme 4). The fragile nature of the lithium ester enolate of dimethyl tartrate acetonide (to β-elimination with loss of acetone) was evident from Seebach’s

Synthesis of the polyketide section of seragamide A and related cyclodepsipeptides via Negishi cross coupling

• Jan Hendrik Lang and
• Thomas Lindel

Beilstein J. Org. Chem. 2019, 15, 577–583, doi:10.3762/bjoc.15.53

• , geodiamolides and seragamides, is reported. The key step is a Negishi cross coupling of (R)-(3-methoxy-2-methyl-3-oxopropyl)zinc(II) bromide and an (E)-iodoalkene that was synthesized via an aluminium ester enolate attack at (R)-propylene oxide. The overall synthesis comprises nine steps with an overall yield

Syn-selective silicon Mukaiyama-type aldol reactions of (pentafluoro-λ⁶-sulfanyl)acetic acid esters with aldehydes

• Anna-Lena Dreier,
• Andrej V. Matsnev,
• Joseph S. Thrasher and
• Günter Haufe

Beilstein J. Org. Chem. 2018, 14, 373–380, doi:10.3762/bjoc.14.25

• : aldol reaction; ester enolate; fluorine; SF5 compounds; stereochemistry; Introduction The classical acid- or base-catalyzed directed cross aldol reaction of an aldehyde and an enolizable second carbonyl compound is one of the most powerful and reliable carbon–carbon bond-forming transformations in

Selected synthetic strategies to cyclophanes

• Sambasivarao Kotha,
• Mukesh E. Shirbhate and
• Gopalkrushna T. Waghule

Beilstein J. Org. Chem. 2015, 11, 1274–1331, doi:10.3762/bjoc.11.142

• , and finally, an intramolecular Michael addition to provide benzannulated large ring compounds 31 and 33. In this regard, substituted methyl 2-alkenyl-2-siloxycyclopropanecarboxylate 29 was converted into the alkylation product and further react with the ester enolate dibromide to yield vinyl

Total synthesis of the proposed structure of astakolactin

• Takayuki Tonoi,
• Keisuke Mameda,
• Moe Fujishiro,
• Yutaka Yoshinaga and
• Isamu Shiina

Beilstein J. Org. Chem. 2014, 10, 2421–2427, doi:10.3762/bjoc.10.252

• ethyl acetate to afford the adduct 19. Diastereoselective methylation of the ester enolate moiety of 19 with MeI afforded only the anti-product 20 [32][33], which was then subjected to the deprotection of the TBDPS group with HF·pyridine, followed by cleavage of the ethyl ester group in 21 to give the

A tandem Mannich addition–palladium catalyzed ring-closing route toward 4-substituted-3(2H)-furanones

• Jubi John,
• Eliza Târcoveanu,
• Peter G. Jones and
• Henning Hopf

Beilstein J. Org. Chem. 2014, 10, 1462–1470, doi:10.3762/bjoc.10.150

• closure towards the formation of 3(2H)-furanone is initiated by the abstraction of the acidic proton by the base and consequent ester enolate attack to the end carbon of the oxy-π-allylpalladium intermediate. Having established an efficient method for the synthesis of highly functionalized furanones from

A convenient enantioselective decarboxylative aldol reaction to access chiral α-hydroxy esters using β-keto acids

• Zhiqiang Duan,
• Jianlin Han,
• Ping Qian,
• Zirui Zhang,
• Yi Wang and
• Yi Pan

Beilstein J. Org. Chem. 2014, 10, 969–974, doi:10.3762/bjoc.10.95

• appears as a common procedure, affording chiral tertiary alcohols which are ubiquitous in the biological sciences and pharmaceutical industry [1][2][3][4][5][6]. The decarboxylative aldol reaction, broadly used for the generation of ester enolate equivalents by the promotion of releasing CO2, has become

Asymmetric organocatalytic decarboxylative Mannich reaction using β-keto acids: A new protocol for the synthesis of chiral β-amino ketones

• Chunhui Jiang,
• Fangrui Zhong and
• Yixin Lu

Beilstein J. Org. Chem. 2012, 8, 1279–1283, doi:10.3762/bjoc.8.144

• alternative decarboxylation–addition pathway at this stage. In fact, in sharp contrast to the popular use of malonic acid half thioesters (MAHTs) as an ester enolate equivalent in enantioselective decarboxylative additions [39], the employment of β-keto acids as a reaction partner in decarboxylative processes

Fused bicyclic piperidines and dihydropyridines by dearomatising cyclisation of the enolates of nicotinyl-substituted esters and ketones

• Heloise Brice,
• Jonathan Clayden and
• Stuart D. Hamilton

Beilstein J. Org. Chem. 2010, 6, No. 22, doi:10.3762/bjoc.6.22

• endo-orientated ester substituent, and the stereochemistries of 20 are accordingly shown with the ester orientated endo. Conclusion Tethered ketone or ester enolate nucleophiles undergo dearomatising attack on a pyridine ring to yield bicyclic products. Yields are greatest if the enolate is first

An expedient synthesis of 5-n-alkylresorcinols and novel 5-n-alkylresorcinol haptens

• Kirsti Parikka and
• Kristiina Wähälä

Beilstein J. Org. Chem. 2009, 5, No. 22, doi:10.3762/bjoc.5.22

• few papers have reported Wittig reactions in water without an organic solvent, although the related Horner-Wadsworth-Emmons reactions, using ester enolate type stabilized phosphonate ylids, have often been conducted in aqueous solutions [29]. The existing cases have mostly been targeted for the

Synthesis of new C^α-tetrasubstituted α-amino acids

• Andreas A. Grauer and
• Burkhard König

Beilstein J. Org. Chem. 2009, 5, No. 5, doi:10.3762/bjoc.5.5

• sulfonium salt 1 and an aldehyde. Applying strongly basic conditions leads to the abstraction of the α-proton of the methionine, the aldehyde undergoes nucleophilic attack by the ester enolate and the displacement of the sulfonium salt substituent by the alkoxy group gives the target TAA. To avoid undesired