Synthesis of six-membered silacycles by borane-catalyzed double sila-Friedel–Crafts reaction

• Yafang Dong,
• Masahiko Sakai,
• Kazuto Fuji,
• Kohei Sekine and
• Yoichiro Kuninobu

Beilstein J. Org. Chem. 2020, 16, 409–414, doi:10.3762/bjoc.16.39

• been demonstrated. Keywords: borane; cyclic compound; organosilane; sila-Friedel–Crafts; silylation; Introduction Six-membered silacyclic compounds, such as phenoxasilin and phenothiasilin derivatives, are attractive compounds for applications as organic electronic materials [1][2][3][4], ligands [5

• dilithiated diaryl thioethers with a range of dichlorosilane derivatives (Scheme 1a) [15][16][17][18][19][20][21][22][23][24]. An intramolecular silylation via Si–C bond cleavage can also be used to prepare a variety of six-membered silacyclic derivatives (Scheme 1b) [25]. However, some problems still remain

• -Friedel–Crafts reaction is emerging as a powerful tool for C–H silylation [28][29]. In addition, intra- and intermolecular sila-Friedel–Crafts reactions have been recently developed [30][31][32][33][34][35][36][37][38][39], which have great potential as efficient synthetic strategies to construct

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

• silyl ether, which are derived from the Pd-catalyzed allylic silylation of 2a and the Cu-catalyzed silylation of 1a and the subsequent [1,2]-Brook rearrangement, respectively. In this coupling reaction, (SIPr)CuCl was a slightly better copper complex than (IPr)CuCl (62%), (SIMes)CuCl (60%) and (IMes

A review of asymmetric synthetic organic electrochemistry and electrocatalysis: concepts, applications, recent developments and future directions

• Munmun Ghosh,
• Valmik S. Shinde and
• Magnus Rueping

Beilstein J. Org. Chem. 2019, 15, 2710–2746, doi:10.3762/bjoc.15.264

• 2e− reduction under electrochemical conditions followed by O-silylation and afforded 192 with high diastereoselectivity. Further treatment of 192 with TBAF resulted in highly substituted optically active 193 with concomitant release of chiral auxiliary 194 (Table 1) [105]. Application in the

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

• ,1′S)-5b (Scheme 38) [91]. A two-carbon fragment came from tert-butyl acetate while the required R configuration at C3 in the final product was secured by stereoselective reduction (10:1) of the ketone (2R,1′S)-149 to give the aziridine alcohol (2R,1′R,1''S)-150 as the major product. Silylation of

• with AD-mix-β provided an inseparable 82:18 mixture of diastereoisomers with the diol 196 as a major product. Silylation of the terminal hydroxy group was followed by mesylation of a secondary one to facilitate the piperidine ring closure triggered by hydrogenolytic removal of the chiral auxiliary to

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

• group strategy led us to TES protection at both alcohols, on the basis that this group should be robust enough to withstand the enolate manipulation chemistry, that desilylation of the secondary TES ether during acetonide removal could be restored in the subsequent tertiary alcohol silylation step, that

• and TES groups in hydroxy acetonide 25. Subsequent silylation using TESOTf gave the bis-TES ketone 26, which was not purified but taken on through diazo formation and desilylation to give diazo alcohol 27 (17% from 25). The efficiency of the sequence from hydroxy acetonide 25 to diazo alcohol 27 could

• be improved (to 37%) using ZnCl2 for the initial deprotection and TESCl in the silylation; the latter minimises formation of the undesired silylated six-membered lactol form of 26. The remaining steps to the model core 31 (Scheme 7) closely mirrored our previous racemic synthesis of 31 (from the

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

• with literature data we converted 7 to the free carboxylic acid carrying a TBS-protected hydroxy group at C8 by silylation with TBSOTf/2,6-lutidine, followed by saponification with LiOH. To investigate whether polyketide 7 could be coupled in an unprotected form with the peptide fragment of seragamide

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

• on the glycosylation of silylated heterocyclic bases with acylated (halo)ribofuranoses and Friedel–Crafts catalysts. The main advantage of this method is that the silylation converts polar, often poorly soluble, heterocyclic bases into lipophilic silyl derivatives, resulting in homogeneous reaction

• glycosylation (Figure 3). This intermediate is subsequently approached by Nam from the less hindered side. Subsequently, Franchetti et al. [30] modified the above TMSOTf-protocol by introducing the preliminary silylation of the amide group of Nam, a procedure based on the chemistry developed by Vorbrüggen [24

• ]. This approach was also applied to nicotinic acid (1b), for which the corresponding silyl ester 10b was prepared (Scheme 5) [30]. Nam (1a) was silylated to the bis-silylated nicotinamide 10a using 2 equivalents of TMSCl. The silylation was followed by the reaction of the crude mixture with 1,2,3,5-tetra

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

• ketene acetals of (Z)-configuration 57a–l, arising from O-silylation of the corresponding chelated potassium enolates [60], underwent an efficient [3,3]-sigmatropic rearrangement upon warming to room temperature. After an acidic work-up and treatment of the crude carboxylic acids with

• 60 was converted into glycolate 61 under standard conditions and the latter ester was engaged in the Ireland–Claisen rearrangement. Because the gem-diester substitution at C3 increased the acidity of the proton at C2 in substrate 61 [64], silylation of that position took place under the reaction

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

• )-2 N-Boc protection preceded the cleavage of the oxazolidine ring while silylation of the hydroxy group was necessary before oxidation of the C=C bond (Scheme 9) [58]. Further applications of the ketopinic acid framework as a chiral auxiliary relied on fine tuning of the steric environment around the

• intramolecular lactonization to form 83 by implementation of the Mitsunobu reaction. After opening of the lactone ring with trichloroethanol and silylation of the hydroxy group oxidation at C5 was performed in the usual way to give a pyroglutamate 84. Benzyl or p-methoxybenzyl esters 85a or 85b were next

Stereodivergent approach in the protected glycal synthesis of L-vancosamine, L-saccharosamine, L-daunosamine and L-ristosamine involving a ring-closing metathesis step

• Pierre-Antoine Nocquet,
• Aurélie Macé,
• Frédéric Legros,
• Jacques Lebreton,
• Gilles Dujardin,
• Sylvain Collet,
• Arnaud Martel,
• Bertrand Carboni and
• François Carreaux

Beilstein J. Org. Chem. 2018, 14, 2949–2955, doi:10.3762/bjoc.14.274

• )-geometry of the crotylboronate, while the 2,3-anti relationship can be rationalized by invoking Cornforth-like transition states [40][41][42][43]. Eventually, silylation of the homoallylic alcohol 12b afforded the expected compound 13b in 68% overall yield from 5 after purification, compared to 29% using a

• the syn diastereomer 18 in high stereoselectivity (93:7). After silylation of the free hydroxy group, the cleavage of the PMB ether with DDQ led to alcohol 20 in 77% yield for the two steps. Ring-closing metathesis of diene 21, obtained by O-vinylation of 20, gave the dihydropyran 22 in 53% overall

Mechanochemistry of nucleosides, nucleotides and related materials

• Olga Eguaogie,
• Joseph S. Vyle,
• Patrick F. Conlon,
• Manuela A. Gîlea and
• Yipei Liang

Beilstein J. Org. Chem. 2018, 14, 955–970, doi:10.3762/bjoc.14.81

• cytosine was also effected following addition of benzoic anhydride and catalytic DMAP to the crude reaction mixture and extending the milling time. Quantitative silylation of 5′-O-dimethoxytritylthymidine under these conditions was also reported. Prompted by the insolubility of adenosine 5′-carboxylic acid

• generally required longer to achieve complete reaction and yielded the corresponding O6,N2,N2-tri-Boc derivatives with variable recoveries (25–70%). The scope of this reaction was extended to unprotected nucleosides by effecting a one-pot, two-step reaction sequence (Scheme 4). Initial transient silylation

• and carboxylic acid Boc protection using an improvised attritor-type mill. Nucleobase Boc protection via transient silylation using an improvised attritor-type mill. Chemoselective N-acylation of an aminonucleoside using LAG in a MBM. Azide–alkyne cycloaddition reactions performed in a copper vessel

Synthesis of a sucrose-based macrocycle with unsymmetrical monosaccharides "arms"

• Karolina Tiara,
• Mykhaylo A. Potopnyk and
• Sławomir Jarosz

Beilstein J. Org. Chem. 2018, 14, 634–641, doi:10.3762/bjoc.14.50

• (19) readily available by a selective silylation of 1’,2,3,3’,4,4’-hexa-O-benzylsucrose (7) [36]. Aldehyde 20 [37] – obtained by Swern oxidation [38] of alcohol 19 – was reacted with amine 17 to afford the desired amine isolated as acetate 21 in 85% total yield. Removal of the TBDPS protecting group

Transition-metal-free [3 + 3] annulation of indol-2-ylmethyl carbanions to nitroarenes. A novel synthesis of indolo[3,2-b]quinolines (quindolines)

• Michał Nowacki and
• Krzysztof Wojciechowski

Beilstein J. Org. Chem. 2018, 14, 194–202, doi:10.3762/bjoc.14.14

• , which in the presence of base (triethylamine or DBU) and trimethylchlorosilane transform into indolo[3,2-b]quinoline derivatives in moderate to good yields. Keywords: carbanions; cyclization; heterocycles; nitroarenes; nucleophilic substitution; silylation; Introduction The indolo[3,2-b]quinoline

• used N-silylated indol-3-ylacetonitrile as a carbanion precursor in the reaction with nitroarenes. Attempts to obtain tert-butyl N-trimethylsilylindol-2-ylacetate via direct silylation of the ester 1c with trimethylchlorosilane was unsuccessful, the product proved unstable and decomposed rapidly. Thus

• , we decided to perform a one-pot reaction in which in situ N-silylation furnished the expected carbanion precursor. Thus, when we treated tert-butyl indol-2-ylacetate (1c) and p-chloronitrobenzene (2a) with triethylamine and potassium tert-butoxide and then added trimethylchlorosilane we obtained

Reagent-controlled regiodivergent intermolecular cyclization of 2-aminobenzothiazoles with β-ketoesters and β-ketoamides

• Irwan Iskandar Roslan,
• Kian-Hong Ng,
• Gaik-Khuan Chuah and
• Stephan Jaenicke

Beilstein J. Org. Chem. 2017, 13, 2739–2750, doi:10.3762/bjoc.13.270

• silylation [72]. In these reactions, the single electron transfer (SET) is initiated by KOt-Bu/DMF [63][67][69][71] or KOt-Bu in combination with additives such as bidentate diamine ligands [61][62][63][64][65], 18-crown-6 [70] or azobisisobutyronitrile (AIBN) [62][66]. Herein, we report the synthesis of

Conjugated nitrosoalkenes as Michael acceptors in carbon–carbon bond forming reactions: a review and perspective

• Yaroslav D. Boyko,
• Valentin S. Dorokhov,
• Alexey Yu. Sukhorukov and
• Sema L. Ioffe

Beilstein J. Org. Chem. 2017, 13, 2214–2234, doi:10.3762/bjoc.13.220

• nitrosoacetals 3 are not halocarbonyl compounds as in the case of oximes 1 and 2, but aliphatic nitro derivatives, which are readily transformed into enamines 3 by double silylation involving an internal redox process [19][20][21]. This allows the preparation of nitrosoalkenes, which are difficult to access by

Phosphonic acid: preparation and applications

• Charlotte M. Sevrain,
• Mathieu Berchel,
• Hélène Couthon and
• Paul-Alain Jaffrès

Beilstein J. Org. Chem. 2017, 13, 2186–2213, doi:10.3762/bjoc.13.219

• -(trimethylsilyl) phosphonate. It is worth noticing that these silylated phosphonates produced quantitatively phosphonic acid derivatives after water or alcohol (methanol, ethanol) treatment [157]. In this initial work, NMR data indicated that silylation of dimethyl or diethyl phosphonate with bromotrimethylsilane

• the terminal oxygen doubly bonded to the phosphorus atom was indeed the nucleophilic atom that attacks the silicon atom [159]. Regarding the mechanism of this reaction, the oxophilic silylation involving the oxygen atom which is doubly bonded to the phosphorus atom, thus producing the intermediate I

• phosphonate moiety. Finally, it must be noted that BrSiMe3 selectively induced the silylation of phosphonate without affecting ketone, amide, halogenoalkane or alkyne [163]. The preparation of phosphonic acid from phosphonate with bromotrimethylsilane was also applied to methylene-tris-phosphonic acids [164

Selective enzymatic esterification of lignin model compounds in the ball mill

• Ulla Weißbach,
• Saumya Dabral,
• Laure Konnert,
• Carsten Bolm and
• José G. Hernández

Beilstein J. Org. Chem. 2017, 13, 1788–1795, doi:10.3762/bjoc.13.173

• lipophilicity, for instance through sulfation [18], silylation or esterification [19] of the aliphatic hydroxy and phenolic groups found in lignin. Chemical esterification of lignin [19][20][21] or its model compounds [22], using acetic anhydride in organic solvents such as DCM or pyridine have previously been

Synthesis of the heterocyclic core of the D-series GE2270

• Christophe Berini,
• Thibaut Martin,
• Pierrik Lassalas,
• Francis Marsais,
• Christine Baudequin and
• Christophe Hoarau

Beilstein J. Org. Chem. 2017, 13, 1407–1412, doi:10.3762/bjoc.13.137

• group from a structurally analog of 9 in DCM as the solvent [20], the Pattenden two-step enol silylation/bromination sequence [23] also found effective to produce consecutively the tert-butyldimethylsilyl enol-ether intermediate from trithiazolylpyridine 9. The latter was treated with NBS reagent in THF

Total synthesis of a Streptococcus pneumoniae serotype 12F CPS repeating unit hexasaccharide

• Peter H. Seeberger,
• Claney L. Pereira and
• Subramanian Govindan

Beilstein J. Org. Chem. 2017, 13, 164–173, doi:10.3762/bjoc.13.19

• [25]. Silylation of the C3 hydroxy group furnished thioglycoside 17. Glycosylation of the C5 linker by activation of 17 using NIS/TfOH as the promoter at −20 °C produced mainly β-mannoside 15 (4:1 β:α) [26]. The identity of the β-isomer was confirmed by NMR analysis (1JCH β = 159.0 Hz, see Supporting

Orthogonal protection of saccharide polyols through solvent-free one-pot sequences based on regioselective silylations

• Serena Traboni,
• Emiliano Bedini and
• Alfonso Iadonisi

Beilstein J. Org. Chem. 2016, 12, 2748–2756, doi:10.3762/bjoc.12.271

• organic synthesis in view of their compatibility with a wide range of conditions. Their regioselective installation on polyols generally requires lengthy reactions and the use of high boiling solvents. In the first part of this paper we demonstrate that regioselective silylation of sugar polyols can be

• of the silylation approach was significantly extended with the development of unprecedented “one-pot” and “solvent-free” sequences allowing the regioselective silylation/alkylation (or the reverse sequence) of saccharide polyols in short times. The developed methodologies represent a very useful and

• protecting groups are featuring the presence of hindered substituents at silicon such as in tert-butyldimethylsilyl (TBDMS) and tert-butyldiphenylsilyl (TBDPS) groups. Their bulkiness allows in many cases regioselective silyl protection of primary alcohols. Commonly, O-silylation is performed by exposing the

Synthesis of polyhydroxylated decalins via two consecutive one-pot reactions: 1,4-addition/aldol reaction followed by RCM/syn-dihydroxylation

• Michał Malik and
• Sławomir Jarosz

Beilstein J. Org. Chem. 2016, 12, 2602–2608, doi:10.3762/bjoc.12.255

• , an alternative approach had to be used to obtain (R)-10. A known procedure based on addition of vinylmagnesium bromide to isopropylidene-protected D-glyceraldehyde followed by silylation and separation of an equimolar mixture of diastereoisomers led to optically pure olefins 21 and 22 (Scheme 5) [51

Synthesis of medronic acid monoesters and their purification by high-performance countercurrent chromatography or by hydroxyapatite

• Elina Puljula,
• Jouko Vepsäläinen and
• Petri A. Turhanen

Beilstein J. Org. Chem. 2016, 12, 2145–2149, doi:10.3762/bjoc.12.204

• synthesis of monoesters. Silylhalides are routinely used for dealkylation [25] of BP esters. Moreover, since the dealkylation reaction by silylation favors sterically less hindered methyl esters over other esters [26], we propose that trimethyl monoalkyl esters could offer a simple route for the synthesis

• with relatively high yields (60–78%). The three methyl ester groups were removed with bromotrimethylsilane at low temperature (<0 °C). The removal of the methylesters by silylation was found not to be fully specific and it led always to the silylation of small amounts of the alkyl ester, despite the

• low silylation temperature. This resulted in mixtures of the desired monoalkylester and medronic acid (5–20%) after the hydrolysis of silyl esters. It was evident that a suitable purification method was needed in order to obtain monoesters with sufficient purity. Two strategies were tested for the

NeoPHOX – a structurally tunable ligand system for asymmetric catalysis

• Jaroslav Padevět,
• Marcus G. Schrems,
• Robin Scheil and
• Andreas Pfaltz

Beilstein J. Org. Chem. 2016, 12, 1185–1195, doi:10.3762/bjoc.12.114

• is available. The subsequent silylation or acylation of the hydroxy group gives access to a library of diverse NeoPHOX ligands. In this way the steric size and the coordination ability of the substituent at the stereogenic center can be tuned for a specific application. Structural motifs of

Carbon–carbon bond cleavage for Cu-mediated aromatic trifluoromethylations and pentafluoroethylations

• Tsuyuka Sugiishi,
• Hideki Amii,
• Kohsuke Aikawa and
• Koichi Mikami

Beilstein J. Org. Chem. 2015, 11, 2661–2670, doi:10.3762/bjoc.11.286

• synthesis of 2,2-difluorostyrenes through Mg(0)-promoted defluorinative silylation followed by fluorine-ion-catalyzed 1,2-desilylative defluorination. Buchwald et al. demonstrated aromatic trifluoromethylation using potassium trifluoroacetate (CF3CO2K), CuI and pyridine under flow conditions. Increasing the

Synthesis of Xenia diterpenoids and related metabolites isolated from marine organisms

• Tatjana Huber,
• Lara Weisheit and
• Thomas Magauer

Beilstein J. Org. Chem. 2015, 11, 2521–2539, doi:10.3762/bjoc.11.273

• prepared by regioselective reduction of the carbonyl group, silylation of the resulting alcohol and further reduction of the enone moiety. An ensuing transetherification of alcohol 59 with ethyl vinyl ether gave an allyl vinyl ether, which underwent a magnesium perchlorate-promoted [1,3]-sigmatropic

• literature-known procedure [47]. Regioselective reduction with sodium borohydride, followed by dehydration under Mitsunobu conditions and silylation of the tertiary alcohol furnished trimethylsiloxy ketone 78. The ketone functionality was then diastereoselectively reduced under Corey–Bakshi–Shibata

• commenced with the preparation of diol 96 by a palladium-catalyzed hydrostannylation of 2-butyne-1,4-diol (95). Regioselective silylation with tert-butyldimethylsilyl chloride of the sterically less hindered alcohol, iodination and silylation of the primary alcohol with trimethylsilyl chloride gave vinyl