A new charge-tagged proline-based organocatalyst for mechanistic studies using electrospray mass spectrometry

• J. Alexander Willms,
• Rita Beel,
• Martin L. Schmidt,
• Christian Mundt and
• Marianne Engeser

Beilstein J. Org. Chem. 2014, 10, 2027–2037, doi:10.3762/bjoc.10.211

• enamine structure II. On the other hand, the comparison with the fragmentation of the structurally related ion [II*b]+ (Figure 5b) is instructive. It doubtlessly possesses an enamine structure since it can neither form a zwitterionic iminium ion nor undergo lactonization to oxazolidinone II’’b because of

Application of cyclic phosphonamide reagents in the total synthesis of natural products and biologically active molecules

• Thilo Focken and
• Stephen Hanessian

Beilstein J. Org. Chem. 2014, 10, 1848–1877, doi:10.3762/bjoc.10.195

• conjugate addition of methanol and lactonization. The second cyclic building block, syn-dihydropyran 188, could be synthesized by a highly diastereoselective 6-endo-trig cyclization of an allylic 1,3-diol, which was developed by Hanessian and co-workers [141]. The required allylic 1,3-diol would also be

Homogeneous and heterogeneous photoredox-catalyzed hydroxymethylation of ketones and keto esters: catalyst screening, chemoselectivity and dilution effects

• Axel G. Griesbeck and
• Melissa Reckenthäler

Beilstein J. Org. Chem. 2014, 10, 1143–1150, doi:10.3762/bjoc.10.114

• acetophenone/methanol reaction: types I–III. Photohydroxymethylation and subsequent lactonization of keto esters. Model reaction for heterogeneous and dye-sensitized catalysis. Product forming routes I to III for photoredox catalysis of methanol/carbonyl compounds. Photoredox initiated steps on semiconductor

Olefin cross metathesis based de novo synthesis of a partially protected L-amicetose and a fully protected L-cinerulose derivative

• Bernd Schmidt and
• Sylvia Hauke

Beilstein J. Org. Chem. 2014, 10, 1023–1031, doi:10.3762/bjoc.10.102

• -benzyloxyhex-5-enal [30], oxidative degradation of aromatics and subsequent lactonization [31], and a two-carbon homologation of an enantiopure C4-building block with a metallated sulfone [32]. A combinatorial biosynthetic approach to D- and L-amicetose has also recently been established by combining different

Isocyanide-based multicomponent reactions towards cyclic constrained peptidomimetics

• Gijs Koopmanschap,
• Eelco Ruijter and
• Romano V.A. Orru

Beilstein J. Org. Chem. 2014, 10, 544–598, doi:10.3762/bjoc.10.50

Decandrinin, an unprecedented C₉-spiro-fused 7,8-seco-ent-abietane from the Godavari mangrove Ceriops decandra

• Hui Wang,
• Min-Yi Li,
• Félix Zongwe Katele,
• Tirumani Satyanandamurty,
• Jun Wu and
• Gerhard Bringmann

Beilstein J. Org. Chem. 2014, 10, 276–281, doi:10.3762/bjoc.10.23

• double bond of int B could yield int C. Finally, the lactonization of int C would give decandrinin (1) (Scheme 1). Experimental General methods Optical rotation values were recorded on a JASCO P-1020 polarimeter. CD spectra were recorded on a J-715 spectropolarimeter (JASCO, Gross-Umstadt, Germany). UV

Recent applications of the divinylcyclopropane–cycloheptadiene rearrangement in organic synthesis

• Sebastian Krüger and
• Tanja Gaich

Beilstein J. Org. Chem. 2014, 10, 163–193, doi:10.3762/bjoc.10.14

• the less substituted double bond using Wilkinson’s catalyst [90] gave α,β-unsaturated ester 87. Removal of the acetate protecting group with concomitant lactonization concluded the total synthesis of tremulenolide A (88), whereas global reduction resulted in the formation of tremulenediol A (89

• underwent smooth, but undesired rearrangement to dihydrooxepin 288. This rearrangement has been observed to be reversible [217]. Treatment with DIBAL-H reduced the carbaldehyde moiety selectively to give alcohol 289. Lactonization was achieved upon Pd-catalyzed CO-insertion to give 290. The desired natural

Synthesis of five- and six-membered cyclic organic peroxides: Key transformations into peroxide ring-retaining products

• Alexander O. Terent'ev,
• Dmitry A. Borisov,
• Vera A. Vil’ and
• Valery M. Dembitsky

Beilstein J. Org. Chem. 2014, 10, 34–114, doi:10.3762/bjoc.10.6

Bidirectional cross metathesis and ring-closing metathesis/ring opening of a C₂-symmetric building block: a strategy for the synthesis of decanolide natural products

• Bernd Schmidt and
• Oliver Kunz

Beilstein J. Org. Chem. 2013, 9, 2544–2555, doi:10.3762/bjoc.9.289

• synthesis of stagonolide E, the MOM-protected precursor 29 and the deprotected derivative 37 were subjected to the Yamaguchi conditions that were found to be successful for the synthesis of 34 and 36 (Scheme 9). While the attempted Yamaguchi lactonization of 37 failed completely and resulted only in the

Silica sulfuric acid: a reusable solid catalyst for one pot synthesis of densely substituted pyrrole-fused isocoumarins under solvent-free conditions

• Sudipta Pathak,
• Kamalesh Debnath and
• Animesh Pramanik

Beilstein J. Org. Chem. 2013, 9, 2344–2353, doi:10.3762/bjoc.9.269

• -catalyzed oxidative lactonization or an intramolecular cyclization reaction of δ-ketoaldehydes [12], a ruthenium-catalyzed aerobic oxidative cyclization of aromatic acids with alkynes [13], an FeCl3-promoted regioselective annulation of o-(1-alkynyl)benzoates with disulfides [14], a Heck–Matsuda cyclization

Study on the total synthesis of velbanamine: Chemoselective dioxygenation of alkenes with PIFA via a stop-and-flow strategy

• Huili Liu,
• Kuan Zheng,
• Xiang Lu,
• Xiaoxia Wang and
• Ran Hong

Beilstein J. Org. Chem. 2013, 9, 983–990, doi:10.3762/bjoc.9.113

• halogen lactonization, as an emerging area, also attracted a lot of attention in recent years [42][43][44]. The two terminal alkenes in compound 10 pose a challenge for chemoselective dioxygenation or iodolactonization. To address this problem, we turn our attention to differentiating the two types of

• ” in a planar amide [41]. In the PIFA-promoted cyclization, lactonization was more likely to be a prominent process than lactamization. Following Tellitu’s procedure [46], we re-synthesized 13 and subjected it to the proton NMR in the presence of D2O. Three proton signals were exchanged with deuterium

Alternaric acid: formal synthesis and related studies

• Michael C. Slade and
• Jeffrey S. Johnson

Beilstein J. Org. Chem. 2013, 9, 166–172, doi:10.3762/bjoc.9.19

• from one of the Lewis basic sulfur atoms, derivatization to a lactone was carried out. The dithiane was cleaved to the ketone 18, which underwent a 1,3-syn-selective reduction [45]. The resultant diol 19 was subjected to acidic conditions to effect cleavage of the tert-butyl ester and lactonization to

The chemistry of bisallenes

• Henning Hopf and
• Georgios Markopoulos

Beilstein J. Org. Chem. 2012, 8, 1936–1998, doi:10.3762/bjoc.8.225

Cyclization of ortho-hydroxycinnamates to coumarins under mild conditions: A nucleophilic organocatalysis approach

• Florian Boeck,
• Max Blazejak,
• Markus R. Anneser and
• Lukas Hintermann

Beilstein J. Org. Chem. 2012, 8, 1630–1636, doi:10.3762/bjoc.8.186

• reaction requires high temperatures (140–250 °C, Scheme 1a) [16][19][20][21][22][23][24][25][26][27][28][29] or photochemical double-bond isomerization (Scheme 1b) [15][17][30][31]. An alternative boron tribromide induced lactonization proceeds at a lower temperature (Scheme 1c), but is not compatible with

A macrolactonization approach to the total synthesis of the antimicrobial cyclic depsipeptide LI-F04a and diastereoisomeric analogues

• James R. Cochrane,
• Dong Hee Yoon,
• Christopher S. P. McErlean and
• Katrina A. Jolliffe

Beilstein J. Org. Chem. 2012, 8, 1344–1351, doi:10.3762/bjoc.8.154

• there are a large number of methods available for macrolactonization reactions, those most commonly employed include the Corey–Nicolaou [19], Boden–Keck [20] and Yamaguchi [21] lactonization procedures. We initially chose to screen these three procedures for the macrolactonization of 5. In all three

Stereoselective synthesis of trans-fused iridoid lactones and their identification in the parasitoid wasp Alloxysta victrix, Part II: Iridomyrmecins

• Robert Hilgraf,
• Nicole Zimmermann,
• Lutz Lehmann,
• Armin Tröger and
• Wittko Francke

Beilstein J. Org. Chem. 2012, 8, 1256–1264, doi:10.3762/bjoc.8.141

• C and D was completed in three additional steps (Scheme 2). The oxidation with Jones reagent yielded 14, and subsequent saponification of the acetate group with methanolic KOH afforded the hydroxy acid 6. Similar to the approach described above, careful lactonization with DCC and DMAP gave

Stereoselective synthesis of trans-fused iridoid lactones and their identification in the parasitoid wasp Alloxysta victrix, Part I: Dihydronepetalactones

• Nicole Zimmermann,
• Robert Hilgraf,
• Lutz Lehmann,
• Daniel Ibarra and
• Wittko Francke

Beilstein J. Org. Chem. 2012, 8, 1246–1255, doi:10.3762/bjoc.8.140

• ] which could be separated by chromatography on silica gel. Hydroboration and lactonization of 12 furnished a mixture of the C4-epimers a and b that once again needed to be separated by chromatography on silica gel [23]. Analytical data of the first eluting component a were in accordance with those

• final lactonization step. Starting from cheap and pure (S)-limonene (14'), the corresponding trans-fused dihydronepetalactones a'–d' could be synthesized in the same way, showing our novel route to be a versatile alternative to Wolinsky’s sequence [20][21]. In contrast to the latter, which fixed the

• phosphate buffer (pH 4.5) afforded the carboxylic acid 25 without epimerization at C1 [23][31]. Subsequent deprotection of the TBDMS ether with tetrabutylammonium fluoride (TBAF) yielded 17, and lactonization with N,N-dicyclohexylcarbodiimide (DCC) and 4-dimethylaminopyridine (DMAP) in dichloromethane

Asymmetric total synthesis of smyrindiol employing an organocatalytic aldol key step

• Dieter Enders,
• Jeanne Fronert,
• Tom Bisschops and
• Florian Boeck

Beilstein J. Org. Chem. 2012, 8, 1112–1117, doi:10.3762/bjoc.8.123

• an acetonide, whereupon lactonization would take place simultaneously. Alkyne 5 could be synthesized through a Sonogashira coupling with iodide 6. This acetonide could be formed by addition of a methyl anion equivalent to the carbonyl group of the aldol product 7 with subsequent protection of the 1,3

• /lactonization sequence opens a new efficient and flexible entry to the coumarin core of other natural products. Furocoumarins. Synthesis of smyrindiol (1) by Grande et al. Synthesis of smyrindiol by Snider et al. Proline-catalyzed intramolecular aldol reaction of O-acetonyl-salicylaldehydes. First

Synthesis of szentiamide, a depsipeptide from entomopathogenic Xenorhabdus szentirmaii with activity against Plasmodium falciparum

• Friederike I. Nollmann,
• Andrea Dowling,
• Marcel Kaiser,
• Klaus Deckmann,
• Sabine Grösch,
• Richard ffrench-Constant and
• Helge B. Bode

Beilstein J. Org. Chem. 2012, 8, 528–533, doi:10.3762/bjoc.8.60

• wanted to synthesize it and make it accessible for additional bioactivity tests. Results and Discussion Synthesis As previous syntheses of depsipeptides showed that lactamization was preferred over lactonization [13][14], the synthesis of 1 was performed as follows: briefly, the linear peptide was

Conserved and species-specific oxylipin pathways in the wound-activated chemical defense of the noninvasive red alga Gracilaria chilensis and the invasive Gracilaria vermiculophylla

• Martin Rempt,
• Florian Weinberger,
• Katharina Grosser and
• Georg Pohnert

Beilstein J. Org. Chem. 2012, 8, 283–289, doi:10.3762/bjoc.8.30

• transformation of arachidonic acid to an 8-hydroperoxide, followed by reduction and elimination of water along with isomerization of the double bonds, could then provide the substrate for lactonization. Since 5 and 6 were configurationally unstable during purification, subsequent isomerizations may lead to the

Efficient oxidation of oleanolic acid derivatives using magnesium bis(monoperoxyphthalate) hexahydrate (MMPP): A convenient 2-step procedure towards 12-oxo-28-carboxylic acid derivatives

• Jorge A. R. Salvador,
• Vânia M. Moreira,
• Rui M. A. Pinto,
• Ana S. Leal and
• José A. Paixão

Beilstein J. Org. Chem. 2012, 8, 164–169, doi:10.3762/bjoc.8.17

• triterpenoids bearing a γ-lactone function, either isolated from natural sources or obtained by semisynthesis, have shown interesting biological activities [12][13][14]. From the synthetic point of view, the oxidative 28,13β-lactonization allows the preparation of 12α-hydroxyoleananes with a protected 28

• of ring C, a strategy known to increase the anti-inflammatory and cytotoxic activities of oleanolic acid (OA) derivatives [19][21][22]. Oleanolic δ-hydroxy-γ-lactones can be obtained from Δ12-oleananes by oxidative 28,13β-lactonization. This reaction was performed under photochemical irradiation [23

• from the β-face, with ring-opening of the 12α,13α-epoxide intermediate [15][44]. Quite recently, we demonstrated that the 28,13β-lactonization of 3-oxooleanolic acid 1 promoted by Bi(OTf)3·xH2O affords a 3-oxo-18α-olean-28,13β-olide product, with inversion of configuration at the C18-stereocenter, as

Asymmetric synthesis of quaternary aryl amino acid derivatives via a three-component aryne coupling reaction

• Elizabeth P. Jones,
• Peter Jones,
• Andrew J. P. White and
• Anthony G. M. Barrett

Beilstein J. Org. Chem. 2011, 7, 1570–1576, doi:10.3762/bjoc.7.185

• gave lactone 12 in 80% yield and 96% ee (Scheme 9). The ability of the alcohol to undergo lactonization under the reaction conditions clearly aided the hydrolysis of this more sterically hindered imidate. We assumed that ketone 6g would also undergo hydrolysis due to its nonbulky nature. However, upon

Amines as key building blocks in Pd-assisted multicomponent processes

• Didier Bouyssi,
• Nuno Monteiro and
• Geneviève Balme

Beilstein J. Org. Chem. 2011, 7, 1387–1406, doi:10.3762/bjoc.7.163

• be in competition with the intramolecular lactonization reaction. The best yields of the expected pyrroles were obtained when the three-component reaction was conducted, with five equivalents of the amine partner, at room temperature in DMF, with PdCl2(PPh3)2/CuI as the catalyst system. The initial C

Gold(I)-catalyzed synthesis of γ-vinylbutyrolactones by intramolecular oxaallylic alkylation with alcohols

• Michel Chiarucci,
• Mirko Locritani,
• Gianpiero Cera and
• Marco Bandini

Beilstein J. Org. Chem. 2011, 7, 1198–1204, doi:10.3762/bjoc.7.139

• alkylation procedure to obtain valuable precursors (i.e., lactams and lactones) of podophyllotoxin analogs [39][40]. However, to the best of our knowledge, no examples of metal-catalyzed lactonization through direct activation of allylic alcohols have been described so far. Results and Discussion At the

• conditions (Table 1). Initial attempts to perform the lactonization reaction of 1a were carried out by means of a silver-free cationic complex [P(t-Bu)2o-biphenyl](AuCH3CN)SbF6 (5 mol %). The desired butyrolactone 2a was obtained selectively under reflux in DCE for 16 h (entry 1), although only in low yield

• lactonization (Table 2). The impact of the carbon–carbon double bond configuration on both chemical and stereochemical outputs of the process was initially investigated. Here, by subjecting (E)-1a to the reaction conditions A (i.e., IMesAuCl/AgOTf, DCE, 80 °C) the corresponding lactone 2a was isolated in

Tandem catalysis of ring-closing metathesis/atom transfer radical reactions with homobimetallic ruthenium–arene complexes

• Yannick Borguet,
• Xavier Sauvage,
• Guillermo Zaragoza,
• Albert Demonceau and
• Lionel Delaude

Beilstein J. Org. Chem. 2010, 6, 1167–1173, doi:10.3762/bjoc.6.133

• complex [RuCl2(=CHPh)(SIMes)(PCy3)], CuCl, and dHbipy (SIMes is 1,3-dimesitylimidazolin-2-ylidene, dHbipy is 4,4'-di-n-heptyl-2,2'-bipyridine) was able to promote the ATRA of trichloroacetic acid onto cyclopentadiene followed by a lactonization into 3,3-dichloro-3,3a,4,6a-tetrahydro-2H-cyclopenta[b]furan

• -2-one (18). These results prompted us to examine the cascade RCM/decomposition/ATRA/lactonization of substrate 16 into dichloro compound 18 with homobimetallic complex 1 under mild thermolysis conditions. Thus, the substrate and the catalyst precursor (5 mol %) were dissolved in toluene and heated