Unusual reactions of diazocarbonyl compounds with α,β-unsaturated δ-amino esters: Rh(II)-catalyzed Wolff rearrangement and oxidative cleavage of N–H-insertion products

• Valerij A. Nikolaev,
• Jury J. Medvedev,
• Olesia S. Galkina,
• Ksenia V. Azarova and
• Christoph Schneider

Beilstein J. Org. Chem. 2016, 12, 1904–1910, doi:10.3762/bjoc.12.180

• appearance of the amides 4 and 7 during the processes studied (Scheme 3). At first, upon catalytic decomposition of diazocarbonyl compounds 2a–c and 3c, N-ylide E is generated, stabilization of which by proton transfer produces an ordinary N–H-insertion product, α-ketoamine F. Similar reactions are well

The hydrolysis of geminal ethers: a kinetic appraisal of orthoesters and ketals

• Sonia L. Repetto,
• James F. Costello,
• Craig P. Butts,
• Joseph K. W. Lam and
• Norman M. Ratcliffe

Beilstein J. Org. Chem. 2016, 12, 1467–1475, doi:10.3762/bjoc.12.143

• body of data for our purposes, as potential FDII will operate under non-buffered, relatively apolar conditions. Though easily stated, the mechanism for the formation of a charged intermediate [5][7][8][9][10][11] followed by attack of water, cleavage of RO–C bonds, and several proton-transfer reactions

Development of chiral metal amides as highly reactive catalysts for asymmetric [3 + 2] cycloadditions

• Yasuhiro Yamashita,
• Susumu Yoshimoto,
• Mark J. Dutton and
• Shū Kobayashi

Beilstein J. Org. Chem. 2016, 12, 1447–1452, doi:10.3762/bjoc.12.140

• biologically active compounds are particularly important. Chiral Lewis acid/Brønsted base-catalyzed carbon–carbon bond-forming reactions are one of the most efficient methods from the viewpoint of atom economy because only proton transfer occurs between starting materials and target products [2]. Several kinds

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

• (Scheme 2B). Furthermore, the high resolution GC–QTOF MS2 analysis of m/z = 179 reveals that the base peak ion is a direct precursor of m/z = 161 by the loss of water (Figure S1, Supporting Information File 1). Starting from cation A1+, a ring opening reaction with a proton transfer to the oxygen may

• opening of A2+ to C2+ followed by a ring expansion to D2+, a proton transfer to E2+ and loss of water to F2+. The fragment ion F2+ is structurally the same as F1+ suggested above for m/z = 161 of 1. This structural identity of F1+ and F2+ is also reflected by the highly similar MS2 spectra of m/z = 161

Reactivity studies of pincer bis-protic N-heterocyclic carbene complexes of platinum and palladium under basic conditions

• David C. Marelius,
• Curtis E. Moore,
• Arnold L. Rheingold and
• Douglas B. Grotjahn

Beilstein J. Org. Chem. 2016, 12, 1334–1339, doi:10.3762/bjoc.12.126

• pyridine was 3.57 pKa units more basic than pyridine [9][10]. Considering reactions other than simple proton transfer, imidazol-2-yl complexes have recently been used to bind to a second transition metal [11]. Additionally, Cp*Ir complexes from our group [12] demonstrated heterolysis of the H–H bond of H2

Conjugate addition–enantioselective protonation reactions

• James P. Phelan and
• Jonathan A. Ellman

Beilstein J. Org. Chem. 2016, 12, 1203–1228, doi:10.3762/bjoc.12.116

• introduction of a proton, the smallest element in the periodic table, presents its own unique challenges. Significant racemic background reactions can compete with the desired enantioselective protonation because proton transfer is among the fastest of all processes. The α-electron withdrawing group, needed to

• intramolecular proton transfer was the stereodetermining step. Alternatively, Sunoj and co-workers performed DFT calculations on the mechanism of the enantioselective Stetter reaction between p-chlorobenzaldehyde and N-acetylamido acrylate and proposed that tert-butyl alcohol plays a key role as the proton

1H-Imidazol-4(5H)-ones and thiazol-4(5H)-ones as emerging pronucleophiles in asymmetric catalysis

• Antonia Mielgo and
• Claudio Palomo

Beilstein J. Org. Chem. 2016, 12, 918–936, doi:10.3762/bjoc.12.90

• ][10][11][12][13]. Regarding reactions which involve proton transfer events, soft enolization [14][15][16] constitutes an efficient tool for the deprotonation of some carbonyl compounds [17][18]. In these cases, a relatively weak amine is generally used to reversibly deprotonate a relatively acidic

Strecker degradation of amino acids promoted by a camphor-derived sulfonamide

• M. Fernanda N. N. Carvalho,
• M. João Ferreira,
• Ana S. O. Knittel,
• Maria da Conceição Oliveira,
• João Costa Pessoa,
• Rudolf Herrmann and
• Gabriele Wagner

Beilstein J. Org. Chem. 2016, 12, 732–744, doi:10.3762/bjoc.12.73

• below for proton transfer. The situation is different in the second mechanism via an eight-membered ring shown in Figure 8 (bottom). There is no need for the carboxylic group to approach the camphor moiety so closely, and the transfer occurs rather in the periphery of the molecule. Consequently, the

• of water is necessary for this step. 2. The fastest tautomerization in the reaction mixture occurs between 7a and 8 (the ene-sulfonamide). The low barriers (8.4 and 10.6 kcal/mol) should allow the equilibrium to be established rapidly. On the other hand, there is no possibility of proton transfer

• compounds as well as carboxylate anions. This is different in the ninhydrin reaction where the corresponding anions lose CO2 upon attempted geometry optimization. Decarboxylation of the imines of the oxoimine 1 only occurs when a zwitterion is formed by proton transfer to one of the two nitrogen atoms. This

Recent advances in N-heterocyclic carbene (NHC)-catalysed benzoin reactions

• Rajeev S. Menon,
• Akkattu T. Biju and
• Vijay Nair

Beilstein J. Org. Chem. 2016, 12, 444–461, doi:10.3762/bjoc.12.47

• anion equivalent 3 is known as the "Breslow intermediate". Its reaction with another molecule of aldehyde leads to the formation of an alkoxide intermediate 4. Proton transfer and subsequent release of thiazolylidene 1 affords the final product, the α-hydroxy ketone 5. Breslow demonstrated that

Dynamic behavior of rearranging carbocations – implications for terpene biosynthesis

• Stephanie R. Hare and
• Dean J. Tantillo

Beilstein J. Org. Chem. 2016, 12, 377–390, doi:10.3762/bjoc.12.41

• rings that are transformed in only one or two enzyme-promoted reactions. These reactions involve generation of a carbocation by protonation or loss of a diphosphate group followed by cyclization, alkyl shift, hydride shift and/or proton transfer reactions to generate new, more complex, carbocations

• [82][83][84][85][86][87][88][89][90] have also been examined computationally [91][92][93]. First, the portion of the C20H33+ PES corresponding to the reactions depicted in Figure 9 was examined with several DFT methods [91]. This study revealed, quite unexpectedly, that intramolecular proton transfer

• these two carbocations proceeds via a TSS that resembles the secondary carbocation expected to be formed upon proton translocation (Figure 9, purple), i.e., the secondary carbocation again corresponds to a TSS rather than a minimum. Direct dynamics trajectories were run from the 1,5-proton transfer

Application of 7-azaisatins in enantioselective Morita–Baylis–Hillman reaction

• Qing He,
• Gu Zhan,
• Wei Du and
• Ying-Chun Chen

Beilstein J. Org. Chem. 2016, 12, 309–313, doi:10.3762/bjoc.12.33

• the identical catalytic conditions [14]. Remarkably, these reactions were usually promoted by bifunctional catalysts, such as β-ICD, whose C6’-OH group served as a H-bond donor to facilitate the proton-transfer step and to stabilize the transition state in MBH reactions [11][12][13][14]. Nevertheless

Facile synthesis of 4H-chromene derivatives via base-mediated annulation of ortho-hydroxychalcones and 2-bromoallyl sulfones

• Srinivas Thadkapally,
• Athira C. Kunjachan and
• Rajeev S. Menon

Beilstein J. Org. Chem. 2016, 12, 16–21, doi:10.3762/bjoc.12.3

• the enone unit to afford the enolate 12. Isomerization of the exocyclic olefin moiety of 12 into the endocyclic position may be assisted by internal proton transfer. Tautomerization of the resultant enol 13 to its keto form affords the final product 8aa. It may be noted that the key carbon–carbon bond

Enantioselective additions of copper acetylides to cyclic iminium and oxocarbenium ions

• Jixin Liu,
• Srimoyee Dasgupta and
• Mary P. Watson

Beilstein J. Org. Chem. 2015, 11, 2696–2706, doi:10.3762/bjoc.11.290

• , this reaction can be carried out in H2O, as well as PhMe. Nearly simultaneously, Knochel’s group reported an enantioselective CuBr/Quinap-catalyzed alkynylation to deliver propargylic amines with alkyl substitution at the stereocenter (Scheme 2) [18][19][20]. In this reaction, proton transfer from the

• ee’s could not be achieved using only a CuOAc/Ph-Pybox catalyst. Postulating that the acetate of CuOAc may facilitate proton transfer from the alkyne to the azomethine imine, a necessary step to form both the cationic iminium and the copper acetylide, Maruoka investigated the use of a chiral acid co

Biocatalysis for the application of CO₂ as a chemical feedstock

• Apostolos Alissandratos and
• Christopher J. Easton

Beilstein J. Org. Chem. 2015, 11, 2370–2387, doi:10.3762/bjoc.11.259

• boidinii FDH due to its stability, the observed turnover for this enzyme is generally low. However, application of a bioelectrochemical system allowed production of formate from CO2 with proton transfer from an electrical source through NAD+ to this FDH [124]. Choe et al. [125][126] showed that a series of

2-Hetaryl-1,3-tropolones based on five-membered nitrogen heterocycles: synthesis, structure and properties

• Yury A. Sayapin,
• Inna O. Tupaeva,
• Alexandra A. Kolodina,
• Eugeny A. Gusakov,
• Vitaly N. Komissarov,
• Igor V. Dorogan,
• Nadezhda I. Makarova,
• Anatoly V. Metelitsa,
• Valery V. Tkachev,
• Sergey M. Aldoshin and
• Vladimir I. Minkin

Beilstein J. Org. Chem. 2015, 11, 2179–2188, doi:10.3762/bjoc.11.236

• diffraction. 2-(2-Benzoxa(thia)zolyl)-6-alkoxycarbonylphenols display intense green fluorescence with anomalous Stokes shifts caused by the excited state intramolecular proton transfer (ESIPT) effects. Keywords: β-tropolones; fluorescence; intramolecular hydrogen bond; tautomerism; X-ray analysis

• -closing step preceded by the formation of the norcaradiene intermediates 8 must include the stage of the proton transfer from the methylene group of the intermediate adduct 7 to the nitrogen atom of the heterocycle. The double proton transfer resulting in the (7A∙AcOH) → (7B∙AcOH) isomerization is the

• proton transfer accompanied by cyclization leads to the norcaradiene derivatives 8∙AcOH, which then rearrange to the dihydrotropolone derivatives 9∙AcOH. In the presence of acetic acid with the twofold excess of o-chloranil, the main channel of the subsequent transformation is determined by the oxidation

Conformational equilibrium in supramolecular chemistry: Dibutyltriuret case

• Karina Mroczyńska,
• Małgorzata Kaczorowska,
• Erkki Kolehmainen,
• Ireneusz Grubecki,
• Marek Pietrzak and
• Borys Ośmiałowski

Beilstein J. Org. Chem. 2015, 11, 2105–2116, doi:10.3762/bjoc.11.227

• existence of life. It is also present in many small molecules acting as an intramolecular configurational lock. This is realized in hydrazones [1], heterocyclic urea derivatives [2], molecules exhibiting photoexcited proton transfer [3] and other compounds [4][5][6] reported also by us [7][8][9][10]. The

• 10. The lack of NH signals in the spectrum may be caused by: a) fast equilibrium or b) the proton transfer between 1 and naphthyridine dianion 10. While the proton transfer is more probable at higher temperatures and lowering the temperature causes the increase of the population of form with

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

• 26, which was subsequently converted to the cyclophane 28 by a Mannich-type condensation reaction (40%) (Scheme 1). Michael addition: In 1999, Reißig and co-workers [85] have synthesized a functionalized cyclophane by a cascade reaction, which proceeds with desilylation, ring opening, proton transfer

Fluoride-driven ‘turn on’ ESPT in the binding with a novel benzimidazole-based sensor

• Kai Liu,
• Xiaojun Zhao,
• Qingxiang Liu,
• Jianzhong Huo,
• Bolin Zhu and
• Shihua Diao

Beilstein J. Org. Chem. 2015, 11, 563–567, doi:10.3762/bjoc.11.61

• proton transfer (ESPT), as an extensively exploited mechanism in many biological and chemical processes, has been employed poorly in anion recognition and sensing [2][11][12][13][14][15][16]. In the ESPT molecules, a five or six-membered intramolecular hydrogen-bonded ring formed, and a proton/hydrogen

• S5 and Figure S6 in Supporting Information File 1). This indicated that the proton transfer from BIP to F− [1]. Meanwhile, the NH signal of BIP at 12.41 ppm was shifted downfield, broadened and weakened, which was ascribed to the formation of an intermolecular hydrogen bond between F− and the above

Microsolvation and sp²-stereoinversion of monomeric α-(2,6-di-tert-butylphenyl)vinyllithium as measured by NMR

• Rudolf Knorr,
• Monika Knittl and
• Eva C. Rossmann

Beilstein J. Org. Chem. 2014, 10, 2521–2530, doi:10.3762/bjoc.10.263

• decayed at or above +3 °C through proton transfer from the solvent that was cleaved into ethylene and the enolate LiO–CH=CH2 [the latter identified through δH = 6.93 ppm (dd) and confirmed by δC = 81.9 and 158.9 ppm]. In t-BuOMe as the solvent, a purified sample of [6Li]4&TMEDA (entry 5, Table 1

• , [15]). The high concentration of (CH3Li)4 did not change during the slow decay of 4&TMEDA at rt through proton transfer from the solvent TMEDA [20][21] that formed olefin 8a, Me2N–CH=CH2, and LiNMe2. In Et2O/hydrocarbons (54:46) without TMEDA, the Sn/Li interchange reaction of 5 and n-Bu6Li was very

Chiral phosphines in nucleophilic organocatalysis

• Yumei Xiao,
• Zhanhu Sun,
• Hongchao Guo and
• Ohyun Kwon

Beilstein J. Org. Chem. 2014, 10, 2089–2121, doi:10.3762/bjoc.10.218

• , facilitating proton transfer and catalyst regeneration in the reaction process. In the case of o-bromophenylimine, even 2.5 mol % of H3 could deliver the corresponding product without any loss of enantioselectivity (95% ee), albeit in slightly lower yield. Jacobsen and Fang proposed a possible transition state

• ylide intermediate. Subsequent proton transfer and β-elimination of the phosphine catalyst results in a γ-functionalized α,β-unsaturated enoate. The reaction, known as γ-umpolung addition, was reported by Trost [100] and Lu [101] in 1994 and 1995, respectively. Trost employed butynoates, which are

Photorelease of phosphates: Mild methods for protecting phosphate derivatives

• Sanjeewa N. Senadheera,
• Abraham L. Yousef and
• Richard S. Givens

Beilstein J. Org. Chem. 2014, 10, 2038–2054, doi:10.3762/bjoc.10.212

• energy is the less reactive and fails to participate in the photo-Favorskii rearrangement. Wan’s work clearly demonstrates, however, that the excited state acidity of 1-naphthols is much greater than 2-naphthols and that excited-state intramolecular proton transfer (ESIPT) for 1-naphthols occurs at both

Proton transfers in the Strecker reaction revealed by DFT calculations

• Shinichi Yamabe,
• Guixiang Zeng,
• Wei Guan and
• Shigeyoshi Sakaki

Beilstein J. Org. Chem. 2014, 10, 1765–1774, doi:10.3762/bjoc.10.184

• (amino)-protonated aminonitrile which occurs with an ΔE≠ value of 34.7 kcal/mol. In the Strecker reaction, the proton transfer along the hydrogen bonds plays a crucial role. Keywords: amide intermediate; DFT calculations; hydrogen bonds; Strecker reaction; transition state; Introduction In 1850, Adolph

• the proton transfer step from HCN to OH−. However, 9 is less stable than 4 by 1.8 kcal/mol, indicating that the OH− prefers to capture a proton from HCN rather than from the NH3+ group. As shown in Figure 2, the rate-determining step of this reaction stage is the proton migration from the NH3+ group

• to the water cluster (from 4 to 5), where the energy barrier is 17.1= [+9.6 − (−7.5)] kcal/mol. Other proton transfer steps facilely occur. These results are in consistent with the room-temperature experimental condition in Scheme 1. For the rate-determining step, we also checked an extended model

An experimental and theoretical NMR study of NH-benzimidazoles in solution and in the solid state: proton transfer and tautomerism

• Carla I. Nieto,
• Pilar Cabildo,
• M. Ángeles García,
• Rosa M. Claramunt,
• Ibon Alkorta and
• José Elguero

Beilstein J. Org. Chem. 2014, 10, 1620–1629, doi:10.3762/bjoc.10.168

• C5/C6) of NH-benzimidazoles that, in some solvents and in the solid state, appear different (blocked tautomerism). In the case of 1H-benzimidazole itself we have measured the prototropic rate in HMPA-d18. Keywords: CPMAS; DNMR; GIAO; proton transfer; tautomerism; Introduction Of almost any class of

• possible to determine the barrier to proton transfer of benzimidazole itself in HMPA-d18, thus providing a missing value in heterocyclic tautomerism of azoles and benzazoles [33]. Experimental Four of the compounds reported in this paper are commercial (Sigma-Aldrich): 1, 2, 3 and 5. We reported the

Preparation of phosphines through C–P bond formation

• Iris Wauters,
• Wouter Debrouwer and
• Christian V. Stevens

Beilstein J. Org. Chem. 2014, 10, 1064–1096, doi:10.3762/bjoc.10.106

• the tertiary amine enables proton transfer from phosphorus to carbon (Table 5). The organocatalyzed hydrophosphination of α,β-unsaturated aldehydes has been described by Carlone et al. [133] and Ibrahem et al. [134]. The method is based on activation of the aldehyde 59 via iminium-ion formation by

• hydrophosphination of vinyl nitriles catalyzed by a dicationic nickel complex (Table 3). The method is based on the activation of the electrophile. It was suggested that complexation of the nitrile 50 to the chiral nickel Lewis acid activates the double bond towards 1,4-addition of the phosphine 25b. A final proton

• transfer yields the phosphine product 51 [124][125]. A chiral Pincer-palladium complex 55 has been used for the addition of diarylphosphines 25c to enones 53 (Table 4) [126]. Several enones 53, having electron-donating or -withdrawing groups on the aromatic ring, reacted with a variety of electron-rich and

Regioselective S_N2' Mitsunobu reaction of Morita–Baylis–Hillman alcohols: A facile and stereoselective synthesis of α-alkylidene-β-hydrazino acid derivatives

• Silong Xu,
• Jian Shang,
• Junjie Zhang and
• Yuhai Tang

Beilstein J. Org. Chem. 2014, 10, 990–995, doi:10.3762/bjoc.10.98

• azodicarboxylates 2 generates the Huisgen zwitterion intermediate 8 [37][38]. Subsequent proton transfer and phosphonium migration between 8 and the MBH alcohol 1 produce an oxophosphonium intermediate 9 and a hydrazine anionic species 10 [36]. Finally, an expedient SN2' attack of species 10 on 9, probably