Architecture and synthesis of P,N-heterocyclic phosphine ligands

• Wisdom A. Munzeiwa,
• Bernard Omondi and
• Vincent O. Nyamori

Beilstein J. Org. Chem. 2020, 16, 362–383, doi:10.3762/bjoc.16.35

• chiral acetal ligands have been reported by Lyle et al. where the fluorine–metal exchange was achieved by treatment with potassium tert-butoxide for a relatively long period (24 h) (Scheme 4) [65]. Acid-catalyzed condensation of compound 20 with enantiomerically pure C2-symmetric 1,2-tosylate analogs 21

• (R = Me, iPr and Ph) in benzene produced chiral acetal 22. Subsequent palladium-catalyzed C–C coupling of the acetal with 4-fluorophenylboronic acid (FPBA) in the presence of caesium carbonate and tri-tert-butylphosphine afforded aryl fluorides 23. Pure ligands 24 (63–72%) were obtained by

• of pyridylphosphine ligands. Synthesis of piperidyl- and oxazinylphosphine ligands. Synthesis of linear multi-chelate pyridylphosphine ligands. Synthesis of chiral acetal pyridylphosphine ligands. Synthesis of diphenylphosphine-substituted triazine ligands. Synthesis of (pyridine-2-ylmethyl)phosphine

Allylic cross-coupling using aromatic aldehydes as α-alkoxyalkyl anions

• Akihiro Yuasa,
• Kazunori Nagao and
• Hirohisa Ohmiya

Beilstein J. Org. Chem. 2020, 16, 185–189, doi:10.3762/bjoc.16.21

• carbonates having a fluoro or acetal substituent were also suitable coupling partners (3ad and 3ae). The synergistic palladium/copper catalysis was used for the reaction of a secondary allylic carbonate. For example, the allylic cross-coupling of 2a’, a constitutional isomer of 2a, with benzaldehyde (1a

SnCl₄-catalyzed solvent-free acetolysis of 2,7-anhydrosialic acid derivatives

• Kesatebrhan Haile Asressu and
• Cheng-Chung Wang

Beilstein J. Org. Chem. 2019, 15, 2990–2999, doi:10.3762/bjoc.15.295

• (Scheme 5). However, the desired acetolysis products 30, 34, and 38 were not obtained. Replacing the more reactive fucose moiety and the benzylidene acetal ring of 29, i.e., using the less reactive complement 33, was also unsuccessful. The branched fucose, benzylidene, and isopropylidene rings of the

• disaccharides were cleaved and acetylated, as shown in Scheme 5. The difficulty of these reactions might have been attributed to the more liable nature of the tertiary acetal center C-1 of fucose as compared to the sterically hindered quaternary ketal functionality C-2 of the 2,7-anhydro skeleton. To our

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

• rearrangement; silyl ketene acetals; Introduction The Ireland–Claisen rearrangement is a reaction converting allyl esters to γ,δ-unsaturated carboxylic acids. Its key step is a [3,3]-sigmatropic rearrangement of a silyl ketene acetal, which is generated in situ by deprotonation of an allyl ester using a strong

• and Discussion We started our investigation with the rearrangement of trimethylsilyl ketene acetal (2a) derived from allyl propionate (1a, Scheme 1). Silyl ketene acetals 2 can be observed by NMR in the reaction mixture (see Supporting Information File 1 for NMR spectra of 2c). This reaction afforded

• , as well as trimethylsilyl ketene acetal 2b generated from 1b, proceeded with similar yields and diastereoselectivity (Table 1, entries 3–6). However, the Ireland–Claisen rearrangement attempted with cinnamyl propionate (1c) did not take place when using LDA as a base (Table 1, entries 7 and 8). Next

Carbazole-functionalized hyper-cross-linked polymers for CO₂ uptake based on Friedel–Crafts polymerization on 9-phenylcarbazole

• Dandan Fang,
• Xiaodong Li,
• Meishuai Zou,
• Xiaoyan Guo and
• Aijuan Zhang

Beilstein J. Org. Chem. 2019, 15, 2856–2863, doi:10.3762/bjoc.15.279

• HCPs include solvent knitting methods [10], Scholl coupling reaction [11], the knitting method with formaldehyde dimethyl acetal (FDA) [12], functional group reactions [2][13] and so on. Among these methods, the knitting method with FDA as external cross-linker is the most time-efficient approach [14

Nanangenines: drimane sesquiterpenoids as the dominant metabolite cohort of a novel Australian fungus, Aspergillus nanangensis

• Heather J. Lacey,
• Cameron L. M. Gilchrist,
• Andrew Crombie,
• John A. Kalaitzis,
• Daniel Vuong,
• Peter J. Rutledge,
• Peter Turner,
• John I. Pitt,
• Ernest Lacey,
• Yit-Heng Chooi and
• Andrew M. Piggott

Beilstein J. Org. Chem. 2019, 15, 2631–2643, doi:10.3762/bjoc.15.256

• ) indicative of a molecular formula C22H36O6. The NMR data for 10 (Table 3) were very similar to those for 3, with the main differences being the absence of a signal for the lactone carbonyl group and the presence of additional signals for acetal (δC 101.9; δH 5.31, t) and methoxy (δC 54.1; δH 3.26, s) groups

• . Key HMBC correlations (Table S12 in Supporting Information File 1) from H-7 to C-12 and from 12-OMe to C-12 positioned the methoxy group and acetal proton on C-12. Thus, the structure of 10 was assigned as shown in Figure 1. The configuration of 10 at C-12 was determined to be 12R based on a key ROESY

A review of the total syntheses of triptolide

• Xiang Zhang,
• Zaozao Xiao and
• Hongtao Xu

Beilstein J. Org. Chem. 2019, 15, 1984–1995, doi:10.3762/bjoc.15.194

• cationic polyene cyclization, transition-metal- or photocatalyst-mediated radical polyene cyclization [72]. The key to such transformation is to install a proper initiator within the substrate such as an allylic alcohol, an acetal, an aziridine, an N-acetal, a hydroxylactam, or a 1,3-dicarbonyl moiety. van

Application of chiral 2-isoxazoline for the synthesis of syn-1,3-diol analogs

• Juanjuan Feng,
• Tianyu Li,
• Jiaxin Zhang and
• Peng Jiao

Beilstein J. Org. Chem. 2019, 15, 1840–1847, doi:10.3762/bjoc.15.179

• oxidation conditions. Based on this assumption, the corresponding silyl nitronate from 3-nitropropanal or its acetal were not tried for cycloaddition. We then set to liberate the β-hydroxy ketone synthon by ring opening of the isoxazoline 3 (Scheme 3). Raney-Ni-catalyzed hydrogenolysis in the presence of

N-(1-Phenylethyl)aziridine-2-carboxylate esters in the synthesis of biologically relevant compounds

• Iwona E. Głowacka,
• Aleksandra Trocha,
• Andrzej E. Wróblewski and
• Dorota G. Piotrowska

Beilstein J. Org. Chem. 2019, 15, 1722–1757, doi:10.3762/bjoc.15.168

• . Acetal formation, reduction of the amide function and deprotection completed synthesis of (−)-hygrine (S)-61. To synthesize (−)-hygroline (2S,2'S)-62 and (−)-pseudohygroline (2S,2'R)-62 the carbonyl group in (S)-66 was reduced and the diastereoisomeric alcohols (2S,2'S)-67 and (2S,2'R)-67 were separated

Electrophilic oligodeoxynucleotide synthesis using dM-Dmoc for amino protection

• Shahien Shahsavari,
• Dhananjani N. A. M. Eriyagama,
• Bhaskar Halami,
• Vagarshak Begoyan,
• Marina Tanasova,
• Jinsen Chen and
• Shiyue Fang

Beilstein J. Org. Chem. 2019, 15, 1116–1128, doi:10.3762/bjoc.15.108

• protected with the 2-cyanoethyl group. These protecting groups and the linker have to be cleaved under strongly basic and nucleophilic conditions. As a result, many sensitive groups including acetal, hemiacetal, vinyl ethers, enol ethers, aldehydes, esters, activated esters, thioesters, aziridines, epoxides

• be protected as a cyclic acetal instead of the more labile acyclic acetal [5][6]. The maleimide group was incorporated into ODNs as a Diels–Alder adduct with dimethylfuran. Besides the need of an additional step for deprotection, only examples of 5'-end modification was given probably due to the

Towards the preparation of synthetic outer membrane vesicle models with micromolar affinity to wheat germ agglutinin using a dialkyl thioglycoside

• Dimitri Fayolle,
• Nathalie Berthet,
• Bastien Doumeche,
• Olivier Renaudet,
• Peter Strazewski and
• Michele Fiore

Beilstein J. Org. Chem. 2019, 15, 937–946, doi:10.3762/bjoc.15.90

• present several advantages compared to natural and synthetic glycolipids, linked by a chemically and enzymatically non-stable acetal function. Owing to their straightforward access, and the stability of thioether conjugates, 1-thio-β--glucopyranose (1a, Figure 1), and 2-acetamido-2-deoxy-1-thio-β

An efficient synthesis of the guaiane sesquiterpene (−)-isoguaiene by domino metathesis

• Yuzhou Wang,
• Ahmed F. Darweesh,
• Patrick Zimdars and
• Peter Metz

Beilstein J. Org. Chem. 2019, 15, 858–862, doi:10.3762/bjoc.15.83

• of the aldehyde function as the dimethyl acetal [16][17][18], hydroboration and oxidative work-up of 10 provided a mixture of epimeric alcohols 11 that was unified by Ley–Griffith oxidation [19] to give ketone 12 [20]. Subsequent Wittig reaction with ylide 13 and acetal cleavage of the resultant

• ), which compares favorably with the previous synthesis of 1 from (+)-dihydrocarvone (10 steps, 6.9% overall yield) [6]. Scheme 3 depicts our first attempts to realize an alternative domino metathesis strategy using enediyne 7. Ozonolysis of the unsaturated acetal 10 gave aldehyde 23 [17][18] that was

• furnish 25 and subsequent acetal hydrolysis provided the known aldehyde 26 [25] in very good overall yield. In our hands, the "demethanation" of (S)-citronellol to produce the primary alcohol corresponding to aldehyde 26 according to the protocol of Abidi (NaNO2, aqueous AcOH) [26] as a potential shortcut

Tuning the stability of alkoxyisopropyl protection groups

• Zehong Liang,
• Henna Koivikko,
• Mikko Oivanen and
• Petri Heinonen

Beilstein J. Org. Chem. 2019, 15, 746–751, doi:10.3762/bjoc.15.70

• chromatography without degradation. The compatibility of these protecting groups in parallel use with benzoyl and silyl groups was verified. The stabilities of the different alkoxy acetal protecting groups were compared by following the kinetics of their hydrolysis at 25.0 °C in buffered solutions through an

• of these acetone-based acetal groups are faster removed than a dimethoxytrityl group, and they are easier to cleave completely in solution. The structural variation allows steering of the stability and lipophilicity of the compounds in some range. Keywords: acetal; hydrolysis; protecting groups

• ; Introduction Acetals form one of the most common types of protecting groups for hydroxy functions. They are easily introduced by a rapid acid-catalyzed reaction and they are also readily cleaved under mild acidic hydrolytic conditions. These properties make the acetal structures usable even in other

Convergent synthesis of the pentasaccharide repeating unit of the biofilms produced by Klebsiella pneumoniae

• Arin Gucchait,
• Angana Ghosh and
• Anup Kumar Misra

Beilstein J. Org. Chem. 2019, 15, 431–436, doi:10.3762/bjoc.15.37

• -azidoethyl 4,6-O-benzylidene-β-D-glucopyranoside (8) [18], prepared from D-glucose, was selectively O-allylated at the 3-hydroxy group by treatment with dibutyltin oxide followed by allyl bromide in the presence of cesium fluoride [19] via the formation of a stannylene acetal to give 2-azidoethyl 3-O-allyl

Syntheses and chemical properties of β-nicotinamide riboside and its analogues and derivatives

• Mikhail V. Makarov and
• Marie E. Migaud

Beilstein J. Org. Chem. 2019, 15, 401–430, doi:10.3762/bjoc.15.36

• presence of a 6 M HCl dioxane solution (almost equimolar amount relative to 4-Me-NR+Cl−) to give the corresponding acetonide in 88% yield. The use of dimethyl acetal of mesitylaldehyde in the presence of catalytic amounts of 10-camphorsulfonic acid in dry DMF was reported [58] but the isolated yield for

Sigmatropic rearrangements of cyclopropenylcarbinol derivatives. Access to diversely substituted alkylidenecyclopropanes

• Guillaume Ernouf,
• Jean-Louis Brayer,
• Christophe Meyer and
• Janine Cossy

Beilstein J. Org. Chem. 2019, 15, 333–350, doi:10.3762/bjoc.15.29

• (7d/7’d = 52:48) were present. An inversion of the face selectivity was detected in favor of diastereomer 7’e (7e/7’e = 43:57) arising from the rearrangement of phosphinite 6e possessing a p-trifluoromethylphenyl substituent. Replacement of the acetal protecting group of the hydroxymethyl substituent

Synthesis of nonracemic hydroxyglutamic acids

• Dorota G. Piotrowska,
• Iwona E. Głowacka,
• Andrzej E. Wróblewski and
• Liwia Lubowiecka

Beilstein J. Org. Chem. 2019, 15, 236–255, doi:10.3762/bjoc.15.22

• hydrolysis, formation of methyl ester and silylation to give 7 after separation from the minor diastereoisomer. After selective hydrolysis of the acetal the hydroxymethyl fragment was oxidized and all protective groups were removed to give (2S,3R)-2 as the hydrochloride (Scheme 1). The observed

• . Intermediary diacid was first esterified with diazomethane, then the isopropylidene acetal was hydrolyzed, and diester saponification gave N-Boc-protected compound (2S,3R)-35. Via ketopinic acid functionalized 2(3H)-oxazolones When oxazolone 36 derived from (R)-(−)-ketopinic acid was reacted with bromine and

• –Eistert reaction to give the methyl ester 59 from which benzyl ester 60 was obtained for easy hydrogenolytic removal in the last step. Hydrolysis of the isopropylidene acetal was followed by periodate cleavage of the C1–C2 bond in the furanose, oxidation of the already formed aldehyde to the acid and

Olefin metathesis in multiblock copolymer synthesis

• Maria L. Gringolts,
• Yulia I. Denisova,
• Eugene Sh. Finkelshtein and
• Yaroslav V. Kudryavtsev

Beilstein J. Org. Chem. 2019, 15, 218–235, doi:10.3762/bjoc.15.21

• . Changes in the synthetic stage sequence led to variable layer compositions. Various linear and star-shaped (triarm) ABA and ABCBA amphiphilic multiblock copolymers containing acetal-protected sugars (APS) were prepared by the coupling of an end-functionalized ROMP copolymer of norbornene (NB) and APS

• the initiator efficiency. The sacrificial approach also helps to describe the multiblock copolymer structure: owing to the acid-labile acetal group, polymer scission takes place at the point of the dioxepin insertion thus providing an indirect way to detect the monomer location [73]. Supramolecular

Silanediol versus chlorosilanol: hydrolyses and hydrogen-bonding catalyses with fenchole-based silanes

• Falco Fox,
• Jörg M. Neudörfl and
• Bernd Goldfuss

Beilstein J. Org. Chem. 2019, 15, 167–186, doi:10.3762/bjoc.15.17

• chloride ion is abstracted from 10 and binds via hydrogen bonding to the catalyst (Scheme 6) [45][47]. This leads to an ion pair [cat•Cl]− and [isoquinolinium cation]+ (Scheme 6). The nucleophilic silyl ketene acetal reacts with the [isoquinolinium cation]+ and forms the C–C bond, yielding product 12

• (Scheme 6 vs Scheme 7). The catalyst abstracts and binds the chloride anion and forms an ion pair [cat•Cl]− and oxocarbenium ion [18]+. Silyl ketene acetal 11 reacts with this ion pair complex to product 19 [77][78]. Only with DCM as solvent, product 19 of the reaction has been isolated (Table 10

• ). Silanediol 9 and silyl ketene acetal 11a provide the highest yield (85%, Table 10, entry 5). The substitution pattern on the silyl ketene has a direct influence on the yield. The highest yield is reached with TMS substitution (silanediol 9, 85% yield, Table 10, entry 5; chlorosilanol 8, 54% yield, Table 10

Adhesion, forces and the stability of interfaces

• Robin Guttmann,
• Johannes Hoja,
• Christoph Lechner,
• Reinhard J. Maurer and
• Alexander F. Sax

Beilstein J. Org. Chem. 2019, 15, 106–129, doi:10.3762/bjoc.15.12

Synthesis of unnatural α-amino esters using ethyl nitroacetate and condensation or cycloaddition reactions

• Glwadys Gagnot,
• Vincent Hervin,
• Eloi P. Coutant,
• Sarah Desmons,
• Racha Baatallah,
• Victor Monnot and
• Yves L. Janin

Beilstein J. Org. Chem. 2018, 14, 2846–2852, doi:10.3762/bjoc.14.263

• 6g–i as well as the lack of compounds 6j–l. Similarly, no condensation was observed when starting with the pyridyl-bearing acetal 5m. These disappointing results are plausibly due to two factors: (i) As mentioned above, the condensation of ethyl nitroacetate (4) with aryl acetals 5 takes place along

• . Indeed, the best overall yields are observed when starting from the electronically similar 2-methoxy acetal 5b or the 4-methoxy analog 5d, as well as the 4-benzyloxy acetal 5e. (ii) Secondly, the reduction of acrylates 2a–s to compounds 6a–s was achieved with sodium borohydride and the resulting basic

Synthesis of pyrrolidine-based hamamelitannin analogues as quorum sensing inhibitors in Staphylococcus aureus

• Jakob Bouton,
• Kristof Van Hecke,
• Reuven Rasooly and
• Serge Van Calenbergh

Beilstein J. Org. Chem. 2018, 14, 2822–2828, doi:10.3762/bjoc.14.260

• -closing metathesis of 24 now smoothly afforded 25 in high yield. Dihydroxylation selectively yielded the desired stereoisomer of diol 26, which was subsequently protected as isopropylidene acetal. In the next step, after removal of the TBS group and mesylation, attempted substitution with NaN3 resulted

Assembly of fully substituted triazolochromenes via a novel multicomponent reaction or mechanochemical synthesis

• Robby Vroemans,
• Yenthel Verhaegen,
• My Tran Thi Dieu and
• Wim Dehaen

Beilstein J. Org. Chem. 2018, 14, 2689–2697, doi:10.3762/bjoc.14.246

• yielding 13 in 51% yield. Since aldehydes are interesting and versatile functional moieties for further derivatization, e.g., used in the synthesis of heterocyclic scaffolds [33][34][50], several multicomponent reactions [40][51][52][53], etc., we wished to convert dimethyl acetal 5j into aldehyde appended

Synthesis of indolo[1,2-c]quinazolines from 2-alkynylaniline derivatives through Pd-catalyzed indole formation/cyclization with N,N-dimethylformamide dimethyl acetal

• Antonio Arcadi,
• Sandro Cacchi,
• Giancarlo Fabrizi,
• Francesca Ghirga,
• Antonella Goggiamani,
• Antonia Iazzetti and
• Fabio Marinelli

Beilstein J. Org. Chem. 2018, 14, 2411–2417, doi:10.3762/bjoc.14.218

• reaction of o-(o-aminophenylethynyl) trifluoroacetanilides with Ar–B(OH)2 afforded 2-(o-aminophenyl)-3-arylindoles, that were converted to 12-arylindolo[1,2-c]quinazolines by adding dimethylformamide dimethyl acetal (DMFDMA) to the reaction mixture after extractive work-up. This reaction outcome is

• 6a) was also isolated. Then, 9a was treated with dimethylformamide dimethyl acetal (DMFDMA) as a source of an electrophilic one-carbon unit at the formate oxidation level [26][27], affording 12-arylindolo[1,2-c]quinazoline 10a in good yield (Scheme 3). Based on this result, we tested an approach to

• accomplished, without competitive formation of products derived from C-3 functionalization at the indole moiety. Synthesis of 6-trifluoromethyl-12-aryl(vinyl)indolo[1,2-c]quinazolines 4. Present and previously reported reactions starting from 5. DMFDMA: dimethylformamide dimethyl acetal. Two-step synthesis of

Cationic cobalt-catalyzed [1,3]-rearrangement of N-alkoxycarbonyloxyanilines

• Itaru Nakamura,
• Mao Owada,
• Takeru Jo and
• Masahiro Terada

Beilstein J. Org. Chem. 2018, 14, 1972–1979, doi:10.3762/bjoc.14.172

• , affording the desired product 2z in moderate yield with formation of inseparable byproducts (Table 4, entry 12). Thus, the use of silyl- and acetal-type protective groups is suitable for the present reaction. As reported previously [13], the fact that the present rearrangement reaction proceeds in a [1,3