Quinone-catalyzed oxidative deformylation: synthesis of imines from amino alcohols

• Xinyun Liu,
• Johnny H. Phan,
• Benjamin J. Haugeberg,
• Shrikant S. Londhe and
• Michael D. Clift

Beilstein J. Org. Chem. 2017, 13, 2895–2901, doi:10.3762/bjoc.13.282

• this reaction sequence, (thio)silyl ketene acetal 10 was united with 2-phenylglycinol and para-anisidine in a two-step, one-pot process to provide β-amino acid derivative 11 in a 60% yield. The overall reaction sequence provides a unique method for the production of the high-value β-amino acid

Synthesis of 1-indanones with a broad range of biological activity

• Marika Turek,
• Dorota Szczęsna,
• Marek Koprowski and
• Piotr Bałczewski

Beilstein J. Org. Chem. 2017, 13, 451–494, doi:10.3762/bjoc.13.48

• rings 3.1 From alkynes The intramolecular, dehydro-Diels–Alder reaction of ketene dithioacetals 302 leading to formation of various benzo[f]-1-indanones 303–305, has been described in 2015 by Bi et al. [117]. Modulation on the reaction parameters such as addition of DBU and the type of atmospheric gas

Dimerization reactions of aryl selenophen-2-yl-substituted thiocarbonyl S-methanides as diradical processes: a computational study

• Michael L. McKee,
• Grzegorz Mlostoń,
• Katarzyna Urbaniak and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2017, 13, 410–416, doi:10.3762/bjoc.13.44

• -membered heterocycles [2]. In addition, some cycloaliphatic thiocarbonyl S-methanides were shown to react with strongly electron-deficient cyano-substituted ethenes via zwitterionic intermediates to yield also seven-membered cyclic ketene imines, which easily undergo further conversions [3][4][5]. In the

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

• -workers reported the use of N-alkylated 3,5-di(carbomethoxy)pyridinium ions L13 to catalyze the reaction between 1-chloroisochroman and silyl ketene acetals (Scheme 10A). Catalyst L13 with R3 = C6F5 was found to be particularly active, and was found to efficiently form the product at 2 mol % loading

• followed by anion exchange. The resultant oxocarbenium/tetraphenylborate ion pair undergoes a nucleophilic attack by silyl ketene acetal, which is followed by scavenging the trimethylsilyl cation with a chloride anion to result in chlorotrimethylsilane and the product. Mechanistic studies were conducted to

• bond donors. However, catalytic halogen scavenging with halogen bond donors is also possible if the products are not inhibiting the catalyst. One of such transformations explored by the Huber group is the addition of ketene silyl acetals to 1-chloroisochroman (Scheme 17) [85][87]. The chloride anion

A new paradigm for designing ring construction strategies for green organic synthesis: implications for the discovery of multicomponent reactions to build molecules containing a single ring

• John Andraos

Beilstein J. Org. Chem. 2016, 12, 2420–2442, doi:10.3762/bjoc.12.236

• cyclohexenone, followed by hydrogenation is 100% atom economical yielding no byproducts. The next best route with an 86% atom economy is the Diels–Alder addition of ketene, generated by pyrolysis of acetone, to 1,3-butadiene to give cyclohex-3-enone, which upon hydrogenation yields cyclohexanone. The only

• Schemes S1 to S3. Among these options the [2 + 2 + 2] strategy of coupling ketene and two equivalents of ethylene is by far the most efficient with an atom economy of 86%. This route matches the closely related second-best performing [4 + 2] route shown in the third entry of Scheme 2. Again, we can

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

• Int B gave the desired β-lactam 3. On the other hand, the possibility of alternative mechanism could not be denied which concerned with the formation of ketene from Int A to give the β-lactam, directly. However, we thought that the reaction proceeded through the above mechanism, because our previous

The EIMS fragmentation mechanisms of the sesquiterpenes corvol ethers A and B, epi-cubebol and isodauc-8-en-11-ol

• Patrick Rabe and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2016, 12, 1380–1394, doi:10.3762/bjoc.12.132

• abbreviated by PMA135(179)). The fragmentation of A1+ may proceed via cleavage of two bonds to G1+, followed by loss of ketene via inductive cleavage and of two hydrogens by α-cleavage to yield H1+. The formation of diradicals that may be highly transient species and are shown in brackets in Scheme 2, can be

• different parts of 1 is active. Two inductive cleavages of F1+ with neutral loss of propene result in I1+. Starting from G1+, a similar reaction as described above for H1+ (m/z = 135) involves the neutral loss of ketene by inductive cleavage, and loss of one hydrogen and one methyl group by α-cleavages to

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

• aldehyde 67 in six steps in 34% yield. After saponification of the ester functionality, treatment with tosyl chloride and trimethylamine resulted in the formation of a ketene that underwent a diastereoselective intramolecular [2 + 2] cycloaddition to provide bicyclic ketone 69. Addition of TMS cerium

• -catalyzed conjugate addition of silyl ketene acetal 81a to enone ent-80. Deprotonation and trapping of the resulting enolate with formaldehyde furnished lactone 82 in a regio- and stereoselective fashion. Introduction of the exocyclic double bond proved to be challenging and therefore salt-free, highly

• afforded coraxeniolide A (10) in 38% yield over three steps. Additionally, the enantioselective total synthesis of β-caryophyllene was realized starting from key intermediate 80. The route commenced with conjugate addition of silyl ketene acetal 81b to enone 80 from the sterically less hindered re-face

Preparation of conjugated dienoates with Bestmann ylide: Towards the synthesis of zampanolide and dactylolide using a facile linchpin approach

• Jingjing Wang,
• Samuel Z. Y. Ting and
• Joanne E. Harvey

Beilstein J. Org. Chem. 2015, 11, 1815–1822, doi:10.3762/bjoc.11.197

• Jingjing Wang Samuel Z. Y. Ting Joanne E. Harvey Centre for Biodiscovery, School of Chemical and Physical Sciences, Victoria University of Wellington, PO Box 600, Wellington 6140, New Zealand 10.3762/bjoc.11.197 Abstract Bestmann ylide [(triphenylphosphoranylidene)ketene] acts as a chemical

• products zampanolide and dactylolide is investigated using Bestmann ylide to link the C16–C20 alcohol with the C3–C8 aldehyde fragment. Keywords: Bestmann ylide; dactylolide; dienoate; (triphenylphosphoranylidene)ketene; zampanolide; Introduction (Triphenylphosphoranylidene)ketene, Ph3P=C=C=O (1), was

• -component reaction between (triphenylphosphoranylidene)ketene (Bestmann ylide, 1), an alcohol and an unsaturated aldehyde delivers α,β,γ,δ-unsaturated esters. This methodology enabled the facile synthesis of E,Z-dienoate products 5b and 5c, which represent two-thirds of the dactylolide/zampanolide

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

• in chlorobenzene yielded bisketenes 325a and 325b. These two ketene derivatives underwent an intramolecular cycloaddition to afford a 1:1 mixture of 326 and 327 (96%, Scheme 57). On heating with concentrated HCl, 326 and 327 were transformed to pyrone derivative 328 (89%). A solution of the compound

Azirinium ylides from α-diazoketones and 2H-azirines on the route to 2H-1,4-oxazines: three-membered ring opening vs 1,5-cyclization

• Nikolai V. Rostovskii,
• Mikhail S. Novikov,
• Alexander F. Khlebnikov,
• Galina L. Starova and
• Margarita S. Avdontseva

Beilstein J. Org. Chem. 2015, 11, 302–312, doi:10.3762/bjoc.11.35

• reversibly undergo a 1,5-cyclization to dihydroazireno[2,1-b]oxazoles. Dihydroazireno[2,1-b]oxazoles derived from 3-aryl-2H-azirines and 3-diazoacetylacetone or ethyl diazoacetoacetate are able to cycloadd to acetyl(methyl)ketene generated from 3-diazoacetylacetone under Rh(II) catalysis to give 4,6-dioxa-1

• -azabicyclo[3.2.1]oct-2-ene and/or 5,7-dioxa-1-azabicyclo[4.3.1]deca-3,8-diene-2-one derivatives. According to DFT calculations (B3LYP/6-31+G(d,p)), the cycloaddition can involve two modes of nucleophilic attack of the dihydroazireno[2,1-b]oxazole intermediate on acetyl(methyl)ketene followed by aziridine

• the mechanism of trapping of dihydroazireno[2,1-b]oxazole intermediates by acetyl(methyl)ketene were investigated by the DFT method. Results and Discussion Rhodium(II) carbenoids generated from α-diazoketones or 2-diazo-1,3-diketones react with various nitrogen-containing compounds, such as amines [16

Cross-dehydrogenative coupling for the intermolecular C–O bond formation

• Igor B. Krylov,
• Vera A. Vil’ and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2015, 11, 92–146, doi:10.3762/bjoc.11.13

Recent advances in the electrochemical construction of heterocycles

• Robert Francke

Beilstein J. Org. Chem. 2014, 10, 2858–2873, doi:10.3762/bjoc.10.303

• coupling. In addition to enol ethers 1, vinyl sulfides and ketene acetals have successfully been cyclized according to Scheme 2 [34][35][36]. An interesting modification of this anodic coupling method was achieved by Yoshida, Nokami and co-workers using the “cation pool” concept [37][38][39]. In this

•  24 [72]. In this example, 1,2-benzoquinone derivatives are generated in the presence of ketene N,O-acetals 70. Out of four possible regioisomers, 71a and 71b are exclusively formed (in ratios 71a/71b between 1:1 and 1:2). In a follow-up study, unreacted α-arylated ketene N,O-acetal intermediates (63

• , Scheme 24) have been identified as byproducts [73][74]. Furthermore, it was demonstrated that ketene N,S-acetals can also be employed for indole synthesis, although the use of these substrates is associated with lower yields compared to N,O-acetals [75]. 2.3 Acyl iminium ions and alkoxycarbenium ions in

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

• primary alcohol of the side chain was oxidized with Dess–Martin periodinane (DMP) to give aldehyde 183. The latter was subsequently reacted with trimethylsilyl ketene acetal 184 in the presence of oxazaborolidinone 185 to afford aldol product 186 and the C22-epimer as only isomers in a 1:1 mixture. Dess

Domino reactions of 2H-azirines with acylketenes from furan-2,3-diones: Competition between the formation of ortho-fused and bridged heterocyclic systems

• Alexander F. Khlebnikov,
• Mikhail S. Novikov,
• Viktoriia V. Pakalnis,
• Roman O. Iakovenko and
• Dmitry S. Yufit

Beilstein J. Org. Chem. 2014, 10, 784–793, doi:10.3762/bjoc.10.74

• ) the formation of the monoadducts 8a,c proceeds via the formation of zwitterionic intermediates 7a,c by nucleophilic attack of the azirine nitrogen lone pair on the C=O group of the ketene fragment of intermediate 6a. Interaction of monoadducts 8a,c with ketene 6a leads to the formation of the unstable

• zwitterionic intermediates 9a,c which further cyclize to bisadducts 3a,c. The barriers for addition of the azirine and aziridine nitrogen lone pair of 1a,c, and 8a,c to ketene 6a increase in passing from compounds 1a, 8a to compounds 1c, 8c, because of a decrease in the nucleophilicity of the latter due to the

• , to give derivatives of 1,3-oxazines [34][35][36]. Another route to compounds 4 and 5 could, therefore, involve interaction of dihydropyrazine 11 with ketene 6, leading to the monoadduct 12, which further reacts with a second molecule of 6 to give 2:2 adducts 4 and 5 (Scheme 3, (b)). To evaluate the

Synthesis of (2S,3R)-3-amino-2-hydroxydecanoic acid and its enantiomer: a non-proteinogenic amino acid segment of the linear pentapeptide microginin

• Rajendra S. Rohokale and
• Dilip D. Dhavale

Beilstein J. Org. Chem. 2014, 10, 667–671, doi:10.3762/bjoc.10.59

• -groups to olefinic acid by either asymmetric epoxidation, dihydroxylation or aminohydroxylation [10][11][12][13][14][15], (ii) the asymmetric synthesis of β-lactams by a Staudinger reaction between ketene and imine to give the corresponding amino acids [16], and (iii) the Lewis acid catalyzed

• multicomponent condensation reactions of aldehyde, an amine and ketene silyl acetal derivatives to get the vicinal hydroxylamino acids [17]. In addition, a few strategies employ a chiral pool approach. For example, Wee et al. utilized the zinc-silver-mediated reductive elimination of α-D-lyxofuranosyl

Synthesis of chiral N-phosphinyl α-imino esters and their application in asymmetric synthesis of α-amino esters by reduction

• Yiwen Xiong,
• Haibo Mei,
• Lingmin Wu,
• Jianlin Han,
• Yi Pan and
• Guigen Li

Beilstein J. Org. Chem. 2014, 10, 653–659, doi:10.3762/bjoc.10.57

• esters [6][7][8][9][10]. Up to now, a series of nucleophilic substrates have been reported to react with α-imino esters, such as enamine [11][12][13][14], carbamate ammonium ylide [15], 1,3-dipolar cycle [16], boronic acid [17], acetylide [18], proparygylic anion [19] and ketene silyl acetal [20]. These

One-pot three-component synthesis and photophysical characteristics of novel triene merocyanines

• Christian Muschelknautz,
• Robin Visse,
• Jan Nordmann and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2014, 10, 599–612, doi:10.3762/bjoc.10.51

• the outcome of the sequence. The latter hypothesis of the iminium-ion stabilization obviously influences the lifetime of the zwitterion 13. Furthermore the enamine formed by deprotonation of 9 is a S,N-ketene acetal, which is significantly more nucleophilic than Fischer’s base (7). The higher

• the dipolar intermediate, which is responsible for the bifurcation as supported by computational studies, enamine nucleophiles favorably lead to 1-styryleth-2-enylideneindolones diastereomers for N-methyl-substituted anilides. The S,N-ketene acetal derived from dimethyl benzothiazolium favors the

Silver and gold-catalyzed multicomponent reactions

• Giorgio Abbiati and
• Elisabetta Rossi

Beilstein J. Org. Chem. 2014, 10, 481–513, doi:10.3762/bjoc.10.46

• between isoquinolinium-2-ylamide 43 and keteneimine 57 [79], silver salt plays the usual role of a π-philic catalyst, whereas ketene imine 57 is generated by a well-known procedure involving a copper(I)-catalyzed azide–alkyne [3 + 2] cycloaddition (CuAAC) giving rise to 5-cuprated triazole intermediate 56

Carbenoid-mediated nucleophilic “hydrolysis” of 2-(dichloromethylidene)-1,1,3,3-tetramethylindane with DMSO participation, affording access to one-sidedly overcrowded ketone and bromoalkene descendants^§

• Rudolf Knorr,
• Thomas Menke,
• Johannes Freudenreich and
• Claudio Pires

Beilstein J. Org. Chem. 2014, 10, 307–315, doi:10.3762/bjoc.10.28

• ketene incorporated KOH to afford the potassium salt of 1,1,3,3-tetramethylindan-2-carboxylic acid (the product of a formal hydrolysis). The lithium salt of this key acid is able to acylate aryllithium compounds, furnishing one-sidedly overcrowded ketones along with the corresponding tertiary alcohols

• expulsion of the observed Me2S. The resultant, still unknown di-tert-alkyl ketene 18 appears to have only limited options in this milieu: Taking t-Bu2C=C=O [2] as a model of the slightly less congested ketene 18, a Pummerer-type acylation of DMSO by 18 should require the assistance of a carboxylic acid [33

• with the base-induced O–S bond cleavage during the Pummerer acylation with t-Bu2C=C=O [36], a base-induced decay of 28 can be expected to generate the 2-thioniapropene 29 along with the α-chloroenolate 30 that may produce the ketene 18 (or the unknown acyl choride) and finally (as in Scheme 3) the

Synthesis of the B-seco limonoid core scaffold

• Hanna Bruss,
• Hannah Schuster,
• Rémi Martinez,
• Markus Kaiser,
• Andrey P. Antonchick and
• Herbert Waldmann

Beilstein J. Org. Chem. 2014, 10, 194–208, doi:10.3762/bjoc.10.15

• pseudo-axial to avoid allylic A1,2-strain, the sigmatropic rearrangement occurred via a pseudo-axial attack of the silyl ketene acetal on the double bond in the cyclohexene ring. These results are in accordance with the observations of Ireland et al. [49], who examined the propensity for axial versus

• , entry 1). Intermediary, the silyl enol ether and the silyl ketene acetal are formed. However, after the rearrangement, the keto-functionality can be set free again during an acidic work-up. In terms of yield and diastereoselectivity there was no difference observed between rearrangements with

• deprotection, esterification and MOM protection. The Ireland–Claisen rearrangement proceeded smoothly and gave a ca. 1.3:1 (78:79) mixture of diastereomers with the product resulting from the pseudo-axial attack of the silyl ketene acetal being the major diastereomer. In analogy to the results above the

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

• [199] upon treatment with silver benzoate. The intermediate ketene 235 underwent stereospecific DVCPR through transition state 235' under the reaction conditions to give enone 236 in excellent yield. This constituted the first example of the direct formation of an enone through a DVCPR. Stephenson and

Diastereoselectivity in the Staudinger reaction of pentafluorosulfanylaldimines and ketimines

• Alexander Penger,
• Cortney N. von Hahmann,
• Alexander S. Filatov and
• John T. Welch

Beilstein J. Org. Chem. 2013, 9, 2675–2680, doi:10.3762/bjoc.9.303

• careful filtration of the desiccant, the dichloromethane solution of the imine was used in further reactions without purification or separation of unreacted amine or the enamine side product. Ketene imine cycloaddition reactions of α-SF5-substituted aldimines and ketimines Dropwise addition of the crude

• imine 5 resulted only in decomposition. Excess amine 4 that was present was acylated by benzyloxyacetyl chloride to form the corresponding amide. The utility of the ketene–imine cyclization was not limited to aldimines. The addition of SF5Br to the enol acetate of ethyl pyruvate 9 formed ethyl

• been optimized. But the significance of these findings lies not only in the difference in reactivity in comparison with trifluoropropanaldimine but also in the relative diastereoselectivity of the ketene–imine cycloaddition reaction in comparison with the other reactions of SF5-bearing aldehydes [16

Reaction of 2,2,4,4-tetrakis(trifluoromethyl)-1,3-dithiethane with N-vinyl compounds

• Viacheslav A. Petrov and
• Will Marshall

Beilstein J. Org. Chem. 2013, 9, 2615–2619, doi:10.3762/bjoc.9.295

• sulfides, cyclic dienes and styrenes [1][2], fluoride anion-catalyzed reactions of compound 1 with vinyl ethers [1][3][4], vinyl sulfides [3], ketene dimethylacetal [5], styrenes [6][7], cyclic dienes [8] and quadricyclane [9]. At this point, no data for the reaction of HFTA or HFTA dimer with vinylamines

Total synthesis of (−)-epimyrtine by a gold-catalyzed hydroamination approach

• Thi Thanh Huyen Trinh,
• Khanh Hung Nguyen,
• Patricia de Aguiar Amaral and
• Nicolas Gouault

Beilstein J. Org. Chem. 2013, 9, 2042–2047, doi:10.3762/bjoc.9.242

• rearrangement was then carried out by using silver nitrate in THF to give the intermediate ketene which was trapped with N,O-dimethylhydroxylamine to provide the corresponding Weinreb amide 1 in 84% yield over two steps. In the next step, the Weinreb amide 1 was added to a solution of O-protected 1-hexynol