Chemo-enzymatic total synthesis: current approaches toward the integration of chemical and enzymatic transformations

• Ryo Tanifuji and
• Hiroki Oguri

Beilstein J. Org. Chem. 2024, 20, 1693–1712, doi:10.3762/bjoc.20.151

• oxidation with the incorporation of a ketone at the C13 position yielded brassicicene A (23). After conversion of 23 into the corresponding silyl enol ether, Rubottom oxidation allowed completion of the total synthesis of brassicicene R (24). As an effort to explore the biomimetic rearrangement, analogous

Domino reactions of chromones with activated carbonyl compounds

• Peter Langer

Beilstein J. Org. Chem. 2024, 20, 1256–1269, doi:10.3762/bjoc.20.108

• two silyl enol ether moieties, can be regarded as masked dianions or electroneutral equivalents of 1,3-dicarbonyl dianions and react with the same regioselectivity [13][14][15][16][17][18][19][20][21][22]. Both free and masked dianions were studied extensively in my group for many years. 1,3-Bis

• (silyloxy)-1,3-butadienes are highly moisture sensitive compounds which can be prepared from the corresponding 1,3-dicarbonyl dianions in two steps. For example, diene 6a is available by silylation of 2 to give silyl enol ether 5 which is subsequently deprotonated by LDA and treated with

Ligand effects, solvent cooperation, and large kinetic solvent deuterium isotope effects in gold(I)-catalyzed intramolecular alkene hydroamination

• Ruichen Lan,
• Brock Yager,
• Yoonsun Jee,
• Cynthia S. Day and
• Amanda C. Jones

Beilstein J. Org. Chem. 2024, 20, 479–496, doi:10.3762/bjoc.20.43

• behaves accordingly here [66]. Specific gold–oxygen interactions are typically not invoked in mechanistic discussions, though a gold alcohol complex has been proposed in silyl enol ether protonation [67]. Equilibrium studies by Maier et al. indicate that methanol is more weakly coordinating than alkynes

Mechanisms for radical reactions initiating from N-hydroxyphthalimide esters

• Carlos R. Azpilcueta-Nicolas and
• Jean-Philip Lumb

Beilstein J. Org. Chem. 2024, 20, 346–378, doi:10.3762/bjoc.20.35

• , Shang and Fu initially demonstrated this approach by utilizing catalytic amounts of triphenylphosphine (PPh3) and sodium iodide (NaI) [67]. Upon formation of EDA complex 80, radical addition to silyl enol ether 81 was promoted under blue light irradiation, affording acetophenone product 82 (Scheme 16A

Enolates ambushed – asymmetric tandem conjugate addition and subsequent enolate trapping with conventional and less traditional electrophiles

• Péter Kisszékelyi and
• Radovan Šebesta

Beilstein J. Org. Chem. 2023, 19, 593–634, doi:10.3762/bjoc.19.44

Formal total synthesis of macarpine via a Au(I)-catalyzed 6-endo-dig cycloisomerization strategy

• Jiayue Fu,
• Bingbing Li,
• Zefang Zhou,
• Maosheng Cheng,
• Lu Yang and
• Yongxiang Liu

Beilstein J. Org. Chem. 2022, 18, 1589–1595, doi:10.3762/bjoc.18.169

• be synthesized from silyl enol ether compound 10 via the Au(I)-catalyzed cycloisomerization reaction developed by our group [15]. The compound 10 could be constructed by the Sonogashira coupling reaction from readily prepared iodoarene 8 [12][16] and ketone 5, which could be synthesized by using

Vicinal ketoesters – key intermediates in the total synthesis of natural products

• Marc Paul Beller and
• Ulrich Koert

Beilstein J. Org. Chem. 2022, 18, 1236–1248, doi:10.3762/bjoc.18.129

• ]. The α-ketoester 41 was accessible from amide 38, which in turn was obtained from allylic alcohol 37. Oxidation and Horner–Wadsworth–Emmons reaction with phosphonate 39 delivered the silyl enol ether 40, which was deprotected and cyclized via a Grubbs metathesis to α-ketoester 41. Subsequent

Synthesis of α-(perfluoroalkylsulfonyl)propiophenones: a new set of reagents for the light-mediated perfluoroalkylation of aromatics

• Durbis J. Castillo-Pazos,
• Juan D. Lasso and
• Chao-Jun Li

Beilstein J. Org. Chem. 2022, 18, 788–795, doi:10.3762/bjoc.18.79

• , while other synthetic approaches were explored to obtain these reagents, the SN2 strategy described in this work was the most efficient. Such synthetic alternatives included: first, a sulfur(VI) fluoride exchange (SuFEx) between perfluoroalkylsulfonyl fluorides and the corresponding silyl enol ether

Strategies for the synthesis of brevipolides

• Yudhi D. Kurniawan and
• A'liyatur Rosyidah

Beilstein J. Org. Chem. 2021, 17, 2399–2416, doi:10.3762/bjoc.17.157

• acid (17) (Scheme 4). The β-hydroxy moiety in 44 can be installed via Sharpless dihydroxylation of the silyl enol ether derived from ketone 45. The 5,6-dihydro-α-pyrone group in ketone 45 is envisaged from protected diol 46 by the sequence of Mitsunobu esterification, ring-closing metathesis, and base

• followed by addition of TBSOTf at low temperature successfully formed the (Z)-silyl enol ether 54. Application of the Sharpless asymmetric dihydroxylation, promoted by AD-mix-β, gave the expected β-(R)-hydroxy cyclopropyl product 55 in 84% yield with moderate diastereoselectivity (dr = 2). The formation of

Advances in mercury(II)-salt-mediated cyclization reactions of unsaturated bonds

• Sumana Mandal,
• Raju D. Chaudhari and
• Goutam Biswas

Beilstein J. Org. Chem. 2021, 17, 2348–2376, doi:10.3762/bjoc.17.153

• oxazolidine derivatives. Cyclization of amide derivatives induced by Hg(OAc)2. Hg(OAc)2/Hg(TFA)2-promoted cyclization of salicylamide-derived amidal auxiliary derivatives. Hg(II)-salt-mediated cyclization to form dihydrobenzopyrans. HgCl2-induced cyclization of acetylenic silyl enol ether derivatives

• enol ether derivative 79 forming carbocyclic compounds 81 with good yields via intermediate 80 [78]. The cyclization of compounds 79 undergo regioselective addition with the triple bond in exocyclic alkene position leading to the formation of α-mercury ketone 80, which were later functionalized by

• hydrated products instead of cyclized thiochromene derivatives. Balasubramanian et al. had performed a mercuric-oxide-mediated cyclization of 1,6-di(aryloxy)-2,4-hexadiyne derivatives 77 to get bichromene derivatives 78 (Scheme 25) [77]. A HgCl2-induced cyclization also takes place for acetylenic silyl

A comprehensive review of flow chemistry techniques tailored to the flavours and fragrances industries

• Guido Gambacorta,
• James S. Sharley and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2021, 17, 1181–1312, doi:10.3762/bjoc.17.90

• been demonstrated to yield superior results to batch. Higher yields and rates of reaction, and greater selectivities can often be achieved in flow. For example, the rate of the aldol reaction of a silyl enol ether 13 with 4-bromobenzaldehyde (14) showed a marked increase upon transposition to flow [87

N-tert-Butanesulfinyl imines in the asymmetric synthesis of nitrogen-containing heterocycles

• Joseane A. Mendes,
• Paulo R. R. Costa,
• Miguel Yus,
• Francisco Foubelo and
• Camilla D. Buarque

Beilstein J. Org. Chem. 2021, 17, 1096–1140, doi:10.3762/bjoc.17.86

Prins cyclization-mediated stereoselective synthesis of tetrahydropyrans and dihydropyrans: an inspection of twenty years

• Asha Budakoti,
• Pradip Kumar Mondal,
• Prachi Verma and
• Jagadish Khamrai

Beilstein J. Org. Chem. 2021, 17, 932–963, doi:10.3762/bjoc.17.77

• introducing a silyl enol ether Prins cyclization concept in which oxocarbenium ion 214, generated by reacting hydroxy-substituted silyl enol ether 212 with aldehyde 213 (different types of aliphatic and aromatic as well as α,β-unsaturated aldehydes were used), was trapped by silyl enol ether [94]. A detailed

• mechanism similar to simple Prins cyclization, except trapping of oxocarbenium ion 214 with silyl enol ether instead of olefin, vinylsilane, or allylsilanes, was proposed as shown in Scheme 51. However, the reaction of silyl enol ether such as 216, upon reacting with an unsaturated aldehyde 217, produced a

CF₃-substituted carbocations: underexploited intermediates with great potential in modern synthetic chemistry

• Anthony J. Fernandes,
• Armen Panossian,
• Bastien Michelet,
• Agnès Martin-Mingot,
• Frédéric R. Leroux and
• Sébastien Thibaudeau

Beilstein J. Org. Chem. 2021, 17, 343–378, doi:10.3762/bjoc.17.32

• can be trapped by TMSCN to furnish α-(trifluoromethyl)-α-aminonitrile 183 in 40% yield. The iminium was also successfully trapped by a silyl enol ether, affording a mixture of ketone 184 and heterocycle 185 (Scheme 44). The trifluoromethyl-substituted derivatives 186a–c have then been exploited as a

Progress in the total synthesis of inthomycins

• Bidyut Kumar Senapati

Beilstein J. Org. Chem. 2021, 17, 58–82, doi:10.3762/bjoc.17.7

• iii) an asymmetric Mukaiyama–Kiyooka aldol reaction (Scheme 16 and Scheme 17) [8]. The total synthesis was initiated with the preparation of two alkenes precursors (rac)-118 and 121. The tiglic aldehyde 115 was converted into silyl enol ether 116 followed by treatment with acetal 117 using a

• diastereoisomers. Then, the key aldol reaction of 123 with silyl enol ether 53 under optimized Mukaiyama–Kiyooka conditions, followed by TIPS deprotection, afforded adduct (3R)-(+)-11 in 63% yield and with 94% ee. Ester hydrolysis followed by acetylation of (3R)- (+)-11 produced acid derivative (+)-76 [50] in 87

Photoredox-catalyzed silyldifluoromethylation of silyl enol ethers

• Vyacheslav I. Supranovich,
• Vitalij V. Levin and
• Alexander D. Dilman

Beilstein J. Org. Chem. 2020, 16, 1550–1553, doi:10.3762/bjoc.16.126

• -electron oxidation thereby supporting a photoredox cycle [22][23][24]. The silyl enol ether 2a derived from acetophenone was selected as a model substrate and the reaction with silane 1 (1.5 equiv) was evaluated (Scheme 2). The reactions were performed in dichloromethane, and reaction mixtures were

• starting enol ether. Moreover, a further increase in reaction time was accompanied by a decrease in the product yield. Finally, GC monitoring suggested complete consumption of the silyl enol ether within 6 hours. It should also be pointed out that the addition of basic additives, which are frequently

• strongly reducing catalysts may be associated with the ability of gold to interact with the bromine atom of silane 1 followed by inner-sphere electron transfer [27]. The radical then attacks silyl enol ether 2, and the subsequent silyloxy-substituted radical is oxidized by the photocatalyst to generate the

Synthesis of acremines A, B and F and studies on the bisacremines

• Nils Winter and
• Dirk Trauner

Beilstein J. Org. Chem. 2019, 15, 2271–2276, doi:10.3762/bjoc.15.219

• traced back to silyl enol ether 10. Ent-10 was first reported by Herzon and co-workers [9] and is derived from phenol silyl ether 11 via Birch reduction and dihydroxylation. Results and Discussion Our synthesis started with meta-cresol (12) which was protected as a TIPS ether and then subjected to Birch

Diastereo- and enantioselective preparation of cyclopropanol derivatives

• Marwan Simaan and
• Ilan Marek

Beilstein J. Org. Chem. 2019, 15, 752–760, doi:10.3762/bjoc.15.71

• cyclopropanol by Cottle [7], the most popular methods for the preparation of cyclopropanols rely on the transformation of enolates [8][9], silyl enol ether [10][11][12], vinyl borane [13][14][15][16][17], Fischer carbene addition [18], addition of nucleophiles to carbonyl groups [19][20][21][22][23][24][25

The LANCA three-component reaction to highly substituted β-ketoenamides – versatile intermediates for the synthesis of functionalized pyridine, pyrimidine, oxazole and quinoxaline derivatives

• Tilman Lechel,
• Roopender Kumar,
• Mrinal K. Bera,
• Reinhold Zimmer and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2019, 15, 655–678, doi:10.3762/bjoc.15.61

• starting material. The efficient conversion of the acetyl group into the corresponding silyl enol ether moiety delivered OX18 that may be used for further transformations. Alternatively, OX7 and phenyl hydrazine afforded the corresponding hydrazone OX19 in excellent yield that was further treated with

6’-Fluoro[4.3.0]bicyclo nucleic acid: synthesis, biophysical properties and molecular dynamics simulations

• Sibylle Frei,
• Andrei Istrate and
• Christian J. Leumann

Beilstein J. Org. Chem. 2018, 14, 3088–3097, doi:10.3762/bjoc.14.288

• that the type of silyl enol ether drastically influenced the yield of the corresponding siloxydifluorocyclopropane. Whereas the TMS enol ethers were not suitable for the reaction due to instability of the silyl group, the tert-butyldimethylsilyl (TBDMS) enol ethers were poorly reactive most likely due

• successful synthesis of the two 6’F-bc4,3 pyrimidine phosphoramidite building blocks 10 and 16 starting from a bicyclic silyl enol ether. The key step in the synthesis was the transformation of a gem-difluorinated tricyclic nucleoside into a ring-enlarged bicyclic fluoroenone by simultaneous desilylation and

Synthesis of cis-hydrindan-2,4-diones bearing an all-carbon quaternary center by a Danheiser annulation

• Gisela V. Saborit,
• Carlos Cativiela,
• Ana I. Jiménez,
• Josep Bonjoch and
• Ben Bradshaw

Beilstein J. Org. Chem. 2018, 14, 2597–2601, doi:10.3762/bjoc.14.237

• presence of bases (e.g., DBU) [12], Pd-catalyzed cycloalkenylation of a silyl enol ether [13], or base-promoted ynone carbocyclizations [14][15]. Another approach through an aldol cyclization, forming the C1–C7a bond instead, has also been reported [16]. Different strategies were developed by Overman

One hundred years of benzotropone chemistry

• Arif Dastan,
• Haydar Kilic and
• Nurullah Saracoglu

Beilstein J. Org. Chem. 2018, 14, 1120–1180, doi:10.3762/bjoc.14.98

Photocatalytic formation of carbon–sulfur bonds

• Alexander Wimmer and
• Burkhard König

Beilstein J. Org. Chem. 2018, 14, 54–83, doi:10.3762/bjoc.14.4

New approaches to organocatalysis based on C–H and C–X bonding for electrophilic substrate activation

• Pavel Nagorny and
• Zhankui Sun

Beilstein J. Org. Chem. 2016, 12, 2834–2848, doi:10.3762/bjoc.12.283

• catalyst with X = I, and R = Oct promoted the reaction between 1-chloroisochroman and silyl enol ether at 0.5 mol % catalyst loadings (70% yield, 6 h). A good correlation was observed between the catalytic activity and halogen affinity, and the Ka of L22 with X = I, R = Oct with bromide anion was

Rh-Catalyzed reductive Mannich-type reaction and its application towards the synthesis of (±)-ezetimibe

• Motoyuki Isoda,
• Kazuyuki Sato,
• Yurika Kunugi,
• Satsuki Tokonishi,
• Atsushi Tarui,
• Masaaki Omote,
• Hideki Minami and
• Akira Ando

Beilstein J. Org. Chem. 2016, 12, 1608–1615, doi:10.3762/bjoc.12.157

• asymmetric Mannich reaction using a Lewis acid catalyst [1]. (L)-Proline is known as an excellent promoter for the Mannich reaction [2][3][4][5][6], and besides this, the reaction of the silyl enol ether derivatives with imines was used as an effective method [7][8][9]. In this situation, a wide variety of