The reductive decyanation reaction: an overview and recent developments

• Jean-Marc R. Mattalia

Beilstein J. Org. Chem. 2017, 13, 267–284, doi:10.3762/bjoc.13.30

• intermediates were trapped using the radical probe 4 (Scheme 4). Replacing t-BuOH with t-BuOD in Scheme 3 (R = CH3 case), yielded the decyanation product 3 with 92% deuterium incorporation. With respect to the mechanism described in Scheme 1, the authors suggest that t-BuOH (or Ph3CH) could act as H-atom donor

• treatment with NaBH4 in 2-propanol by using both basic and nucleophilic properties of the hydride ion. The proposed mechanism involves a double-bond isomerization to the α-aminonitrile intermediate which is then reduced by the hydride ion in a classical way (Scheme 7). Interestingly, deuterium-labelling

• reduction of radical probes (no rearranged products formed from 25d,l,m) and deuterium-labelling experiments (no deuterium incorporation using THF-d8 and quenching with D2O) discard the possibility of a single-electron transfer pathway. Other reductions suggest a hydride addition with formation of an iminyl

Silyl-protective groups influencing the reactivity and selectivity in glycosylations

• Mikael Bols and
• Christian Marcus Pedersen

Beilstein J. Org. Chem. 2017, 13, 93–105, doi:10.3762/bjoc.13.12

• stereoselectivity has been demonstrated in radical reactions, however, with the twist that stereoselectivity here is opposite. The reduction of the selenoglycosides (analogues to 20) with tributyltin deuteride gave predominantly deuterium in the β-position for silylated derivatives in the 1C4 conformation, because

• the reaction intermediate is a radical that prefers to be axial. On the other hand, with acetate protective groups, the addition of deuterium occurred predominantly from the β-side [45][46]. The principle of conformational stereocontrol was also used for the stereoselective addition of carbon radicals

Phosphated cyclodextrins as water-soluble chiral NMR solvating agents for cationic compounds

• Cira Mollings Puentes and
• Thomas J. Wenzel

Beilstein J. Org. Chem. 2017, 13, 43–53, doi:10.3762/bjoc.13.6

• either as hydrochloride salts or neutral compounds. Neutral substrates were converted to their hydrochloride salts in deuterium oxide (D2O) by adding a slight excess of deuterium chloride (DCl). II. Apparatus Proton (1H) NMR spectra were obtained using a Bruker Avance 400 MHz NMR spectrometer. Samples

Effects of solvent additive on “s-shaped” curves in solution-processed small molecule solar cells

• John A. Love,
• Shu-Hua Chou,
• Ye Huang,
• Guilllermo C. Bazan and
• Thuc-Quyen Nguyen

Beilstein J. Org. Chem. 2016, 12, 2543–2555, doi:10.3762/bjoc.12.249

• , resulting in a depth profile. To improve contrast between the two materials, deuterated fullerene PC61BM-d5 was used as a surrogate for PC71BM to establish a unique mass signal for the fullerene component [12][66][67]. Thus detection of deuterium in the mass spectrum implicitly signifies PC61BM-d5 in the

• rate. Thus the x-axis has been scaled for film thickness, where the turn-on of the nitrogen and deuterium signals at x = 0 nm corresponds to the top surface of the films, what would be the cathode interface in a complete device architecture. The turn-off of the signals thus corresponds to the BHJ/PEDOT

• cast from pure chlorobenzene (yellow) and with 1.5% DIO (blue) with (solid) and without (dashed) methanol treatment. Dynamic secondary ion mass spectrometry (DSIMS) profile showing scaled nitrogen (solid) and deuterium (dashed) signals for films cast a) with no DIO and b) with 1.5% DIO. a) A schematic

Protonated paramagnetic redox forms of di-o-quinone bridged with p-phenylene-extended TTF: A EPR spectroscopy study

• Nikolay O. Chalkov,
• Vladimir K. Cherkasov,
• Gleb A. Abakumov,
• Andrey G. Starikov and
• Viacheslav A. Kuropatov

Beilstein J. Org. Chem. 2016, 12, 2450–2456, doi:10.3762/bjoc.12.238

• under such conditions is the proton attached to the semiquinone. Due to deuterium exchange the spectrum transforms into a broadened triplet of triplets (Figure 2b), since the higher spin (S = 3/2) and the small gyromagnetic ratio of the deuterium nucleus (γN = 4.1065 × 103 rad G−1 s−1) renders the

A detailed view on 1,8-cineol biosynthesis by Streptomyces clavuligerus

• Jan Rinkel,
• Patrick Rabe,
• Laura zur Horst and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2016, 12, 2317–2324, doi:10.3762/bjoc.12.225

• in both cases a syn addition, as could be shown by incubation of (2-13C)geranyl diphosphate in deuterium oxide. Keywords: biosynthesis; enzyme mechanisms; isotopic labelling; stereochemistry; terpenes; Introduction Among all classes of natural products the climax of structural diversity and

• or an anti addition to the olefinic double bond, requiring a protonation of the original C-2 of GPP. To distinguish between these alternatives (2-13C)GPP was synthesised from sulcatone (Scheme S2, Supporting Information File 1) and converted by the 1,8-cineol synthase in deuterium oxide. The obtained

• product was analysed by HSQC spectroscopy (Figure 3A), showing that deuterium is taken up into the exo position at the 13C-labelled C-2 of 1 (indicated by H’), while the endo position (H’’) is occupied by the proton from the substrate, resulting in a strong crosspeak [22]. Furthermore, deuterium

Enantioconvergent catalysis

• Justin T. Mohr,
• Jared T. Moore and
• Brian M. Stoltz

Beilstein J. Org. Chem. 2016, 12, 2038–2045, doi:10.3762/bjoc.12.192

• . Deuterium labeling experiments have shown that the hydrogenation reaction occurs only on the chiral keto tautomer, and therefore the catalyst selects one enantiomer of the substrate when the reduction takes place. Enantioconvergent methods are not limited to carbon stereocenters. An exceptional example of

Mechanistic investigations on six bacterial terpene cyclases

• Patrick Rabe,
• Thomas Schmitz and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2016, 12, 1839–1850, doi:10.3762/bjoc.12.173

• containing water or deuterium oxide allowed for detailed insights into the cyclisation mechanisms of the bacterial terpene cyclases. Keywords: absolute configuration; biosynthesis; enzyme mechanisms; structure elucidation; terpenes; Introduction Terpenes are structurally fascinating natural products with

• to 4 (Scheme 1). This biosynthetic model was tested by incubation of (6-13C)FPP with the 7-epi-α-eudesmol synthase in deuterium oxide to follow the reprotonation of the neutral intermediate 4a [54][55]. A simple extraction of the reaction mixture with (2H6)benzene and direct 13C NMR analysis resulted

• in a highfield shifted triplet at 38.7 ppm (Δδ = −0.5 ppm, 1JC,D = 19.4 Hz), demonstrating the introduction of deuterium at C-6 of 4 (Figure 4). The singlet at 39.2 ppm is observed due to residual water in the enzyme reaction. Germacranes have been suggested as general precursors for eudesmanes [56

Cp₂TiCl/D₂O/Mn, a formidable reagent for the deuteration of organic compounds

• Antonio Rosales and
• Ignacio Rodríguez-García

Beilstein J. Org. Chem. 2016, 12, 1585–1589, doi:10.3762/bjoc.12.154

• experimental conditions and with great economic advantages. Keywords: deuteration; deuterium atom transfer; radical and/or organometallic chemistry; titanocene; Introduction Deuterium is a stable isotope of hydrogen with 0.015% natural abundance broadly used in organic chemistry, pharmacology, organometallic

• chemistry, spectroscopy and many other fields [1][2][3][4]. Exchange of hydrogen for deuterium produces primary and secondary kinetic isotope effects (KIE) causing isotopically substituted molecules to react at different rates (kH ≠ kD). This behaviour is due to the differences in bond dissociation energies

• for both species, which in turn, is dependent upon the zero point for the vibrational energy of both isotopic molecules. As the mass of deuterium is about twice the mass of hydrogen there is a larger activation energy for the C–D bond dissociation than for the C–H bond [4]. The KIE observed allows

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

• , introduction of labelling into the various positions of the compound of interest may require a different synthetic strategy for each individual target isotopomer. Most of these studies made use of deuterium labellings that can frequently be introduced into reactive positions of a (functionalised) terpene

• isolated from the producing organism. Deuterium labellings also allow to follow hydrogen rearrangements, but non-specific hydrogen migrations during the fragmentation process and kinetic isotope effects can make data interpretation difficult. In contrast, the introduction of 13C-labelling into a terpene

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

• mechanism of their reaction through a combination of DFT calculations, deuterium labeling studies, and control experiments (Scheme 13) [34]. The authors proposed that after migratory insertion of the rhodium–aryl bond across the acrylate, 58 undergoes β-hydride elimination of the enamide proton to generate

• rhodium catalyst binding to the benzoxazole nitrogen 68. Deuterium labeling studies were performed on the system and based on their results a mechanism was proposed in which the stereodetermining step is a rhodium-hydride transfer instead of protonation of an oxo-π-allylrhodium species (Scheme 17

Synthesis of a deuterated probe for the confocal Raman microscopy imaging of squalenoyl nanomedicines

• Eric Buchy,
• Branko Vukosavljevic,
• Maike Windbergs,
• Dunja Sobot,
• Camille Dejean,
• Simona Mura,
• Patrick Couvreur and
• Didier Desmaële

Beilstein J. Org. Chem. 2016, 12, 1127–1135, doi:10.3762/bjoc.12.109

• squalenoyl gemcitabine nanoparticles displayed significant Raman scattering signals. They revealed no differences except from the deuterium peak patterns in the silent spectral region of cells. This paves the way for label-free intracellular trafficking studies of squalenoyl nanomedicines. Keywords

• : deuterium labelling; nanomedicine; Raman spectroscopy; Shapiro reaction; squalene; Introduction Application of nanotechnology to medicine holds promises to profoundly impact healthcare especially to treat severe diseases such as cancer, intracellular infections, neurodegenerative diseases, etc. Indeed, the

• when dealing with low drug concentrations or biological-like structures such as peptide drugs or nucleoside analogues. To overcome this issue, deuterium can be introduced to a sample molecule, as it exhibits a significant Raman signal at around 2200 cm−1, which is in a so called “silent region” (1800

The synthesis of functionalized bridged polycycles via C–H bond insertion

• Jiun-Le Shih,
• Po-An Chen and
• Jeremy A. May

Beilstein J. Org. Chem. 2016, 12, 985–999, doi:10.3762/bjoc.12.97

• , even when the exocyclic oxygen was acetylated. This is likely related to the effects observed by Lee (Scheme 4). The Adams group also looked for a deuterium kinetic isotope effect for insertion in both 34 (Y = D, X = OMe) and 37 (Y = D, R = H). Only a small difference in relative rates between C–H and

• deuterium kinetic isotope effect of 2.34 was seen for C–H insertion with gold catalysis. Hashmi demonstrated the viability of dual gold catalysis for carbene/alkyne cascades with diynes like 109, which gave products from either a 1,2-methyl shift (not shown) or a C–H bond insertion to form enone 112 (Scheme

Cupreines and cupreidines: an established class of bifunctional cinchona organocatalysts

• Laura A. Bryant,
• Rossana Fanelli and
• Alexander J. A. Cobb

Beilstein J. Org. Chem. 2016, 12, 429–443, doi:10.3762/bjoc.12.46

• organocatalyst with comparable results. More recently, Johnson and co-worker used the o-toluoyl derived organocatalyst CPD-33 to effect a dynamic kinetic asymmetric transformation of racemic β-bromo-α-keto esters 32 (Scheme 9a) [35]. The mechanism, deduced from deuterium labeling studies, proposes that one of

Tandem processes promoted by a hydrogen shift in 6-arylfulvenes bearing acetalic units at ortho position: a combined experimental and computational study

• Mateo Alajarin,
• Marta Marin-Luna,
• Pilar Sanchez-Andrada and
• Angel Vidal

Beilstein J. Org. Chem. 2016, 12, 260–270, doi:10.3762/bjoc.12.28

• are conceivable for explaining these conversions. Deuterium labelling experiments exclude the [1,4]-hydride shift as the first step. A computational study scrutinized the reaction channels of these tandem conversions starting by [1,5]-, [1,7]- and [1,9]-H shifts, revealing that this first step is the

• from those starting by [1,5]-, [1,7]- or [1,9]-H shifts, represented in Scheme 4, by deuterium labelling experiments. Thus, if the conversion of the deuterated acetal-fulvene 14, in which deuterium replaces the proton at the acetalic carbon of 3a, was actually initiated by a [1,4]-deuteride shift, the

• transformation of the dihydrobenzo[f]indenic species 15, which should form in first instance, would yield the final benz[f]indenes via intermediates 16 and 17. These are labelled with deuterium at C4 of the major product 18 and at C9 of the minor one 19 as well as probably at additional positions of the fused

Base metal-catalyzed benzylic oxidation of (aryl)(heteroaryl)methanes with molecular oxygen

• Hans Sterckx,
• Johan De Houwer,
• Carl Mensch,
• Wouter Herrebout,
• Kourosch Abbaspour Tehrani and
• Bert U. W. Maes

Beilstein J. Org. Chem. 2016, 12, 144–153, doi:10.3762/bjoc.12.16

• deuterium incorporation in the benzylic position of 16 and 3h through acid-catalyzed imine–enamine tautomerization is dependent on the strength of the acid used (Figure 1). The rate of deuterium incorporation in 2-benzylpyridine (16, pKa ≈ 5.2) is much faster when using TFA-d1 than with AcOH-d4 [34][35

• ]. With the less basic 2-benzyl-5-chloropyridine (3h, pKa ≈ 3.0) the difference is even more pronounced: Almost no deuterium incorporation could be detected using AcOH-d4 while the reaction ran smoothly using the stronger acid TFA-d1. From this we conclude that when the pyridine nitrogen becomes less

• also reflected in the chemoselectivity studies where DMSO is the only solvent in which oxidation of a (di)azinylmethyl is possible. Hydrogen–deuterium exchange through acid-catalyzed imine–enamine tautomerization of 3h (0.5 M) and 16 (0.5 M) using AcOH-d4 (0.5 M) or TFA-d1 (0.5 M). 1H NMR spectroscopy

Synthesis and reactivity of aliphatic sulfur pentafluorides from substituted (pentafluorosulfanyl)benzenes

• Norbert Vida,
• Jiří Václavík and
• Petr Beier

Beilstein J. Org. Chem. 2016, 12, 110–116, doi:10.3762/bjoc.12.12

• the synthesis of selectively deuterium labelled acrylic acid derivative 23. Indeed, when maleic acid 4 was evaporated twice with D2O to exchange acidic protons and heated in DMSO-d6, deuterated 23 was observed by NMR spectroscopy (Scheme 10). Conclusion In conclusion, similar to 4-(pentafluorosulfanyl

• . Synthesis of maleic anhydride 20 and Diels–Alder adducts 21. Reaction of maleic acid 4 with diazomethane. Decarboxylation of maleic acid 4 to acrylic acid 23 in DMSO and the preparation of deuterium labelled 23. Calculated reaction coordinates of Diels–Alder reaction of 12 with cyclopentadiene.a Supporting

Recent highlights in biosynthesis research using stable isotopes

• Jan Rinkel and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2015, 11, 2493–2508, doi:10.3762/bjoc.11.271

• the product of a polyketide biosynthetic gene cluster [24]. To test whether N-acetylcysteine could be a biosynthetic precursor of the unusual 1,5-oxathiocane structure, feeding experiments using both (2S)- and (2R)-N-((2H3)acetyl)cysteine were performed. The deuterium atoms of both precursors were

• -[2H5,15N]threonine were fed to P. luminescens. The loss of one deuterium atom for an incorporated labeled amino acid (from Cα) directly supports an epimerase function within the corresponding NRPS module, and the incorporated building block can be assigned as D-configured. In this example, epimerization

• EIMS-fragmentation reactions of 34 by comparison of the 13C-including fragments. Singly labeled FPP isotopomers also proved valuable to investigate reprotonation steps in sesquiterpene cyclization mechanisms by incubation in deuterium oxide. The biosynthesis of the recently discovered corvol ethers A

Copper-catalyzed stereoselective conjugate addition of alkylboranes to alkynoates

• Takamichi Wakamatsu,
• Kazunori Nagao,
• Hirohisa Ohmiya and
• Masaya Sawamura

Beilstein J. Org. Chem. 2015, 11, 2444–2450, doi:10.3762/bjoc.11.265

• the α-position of the carbonyl group (93% D). The syn selectivity was slightly decreased due to the deuterium isotope effect: Slower D-trap caused isomerization of organocopper intermediates (vide infra). This experimental result indicates that t-BuOH acts as a proton source. A possible mechanism for

• selectivity. Possible mechanism. Isomerization of the alkenylcopper intermediates. Conjugate addition of alkylborane 2a to alkynoate 3a. Synthesis of five membered carbocycle. Deuterium-labeling experiment. Ligand effects. Copper-catalyzed conjugate addition of alkylboranes 2 to alkynoates 3.a Supporting

New aryloxybenzylidene ruthenium chelates – synthesis, reactivity and catalytic performance in ROMP

• Patrycja Żak,
• Szymon Rogalski,
• Mariusz Majchrzak,
• Maciej Kubicki and
• Cezary Pietraszuk

Beilstein J. Org. Chem. 2015, 11, 1910–1916, doi:10.3762/bjoc.11.206

• signal that could be assigned to the hydroxy group. It is most probably a consequence of high lability of this proton and its suitability for exchange with deuterium coming from the NMR solvent (CD2Cl2) as it was observed for activated complex 1a [9]. Complex 17 was proved to exhibit high catalytic

Preparative semiconductor photoredox catalysis: An emerging theme in organic synthesis

• David W. Manley and
• John C. Walton

Beilstein J. Org. Chem. 2015, 11, 1570–1582, doi:10.3762/bjoc.11.173

• transfer of an electron to the TiO2 will compete with the loss of CO2, thus reducing yields. An intriguing aspect of the process is the source of the H atoms gained during the formation of adducts 22 and 29. This was not the proton lost from the aromatic ring in forming 31. Deuterium labelling experiments

Pyridine-promoted dediazoniation of aryldiazonium tetrafluoroborates: Application to the synthesis of SF₅-substituted phenylboronic esters and iodobenzenes

• George Iakobson,
• Junyi Du,
• Alexandra M. Z. Slawin and
• Petr Beier

Beilstein J. Org. Chem. 2015, 11, 1494–1502, doi:10.3762/bjoc.11.162

• established that the hydrogen atom in the product comes exclusively from THF and not from pyridine or MeCN (Table 4). The observed deuterium enrichment using THF-d8 was around 80%. Thermal decomposition of aryldiazonium salts prepared from immobilized triazene precursors and the formation of deuterated

• from intermolecular competition experiment using 3b and a 1:1 mixture of THF and THF-d8 giving KIE = 5.5 (6:6-D ratio determined by GC–MS) and combined yield of 62%. This means that the hydrogen abstraction is much faster than the deuterium abstraction and suggests the C-H(D) bond formation as the rate

Gold-catalyzed formation of pyrrolo- and indolo-oxazin-1-one derivatives: The key structure of some marine natural products

• Sultan Taskaya,
• Nurettin Menges and
• Metin Balci

Beilstein J. Org. Chem. 2015, 11, 897–905, doi:10.3762/bjoc.11.101

• products we carried out two different reactions. First, 15 was reacted with CD3OD under the same reaction conditions. The 1H NMR spectral analysis indicated the formation of 49 and 50 in 65% and 35% yields, respectively. Furthermore, the amount of deuterium atoms in 49 and 50 attached to the methylene

Superoxide chemistry revisited: synthesis of tetrachloro-substituted methylenenortricyclenes

• Basavaraj M. Budanur and
• Faiz Ahmed Khan

Beilstein J. Org. Chem. 2014, 10, 2531–2538, doi:10.3762/bjoc.10.264

• -di-tert-butyl-4-methylphenol) improved the yields of methylenenortricyclenes. A complete deuterium incorporation was observed in the superoxide-mediated reaction in DMSO-d6. Friedel–Crafts acylation reactions of 3-methylenenorticyclenes yielded 2-propanone-substituted pentachloronorbornenes

• did not yield any product which suggested that there is a unique and exceptional degree of reactivity of the superoxide ion species which triggered this kind of reaction. To elucidate the reaction mechanism, we have performed a deuterium labelling experiment by treating 3c with KO2 in DMSO-d6 at rt

• . Absence of the peak at δ 4.26 (singlet) in 1H NMR suggest the incorporation of deuterium and a triplet at δ 71.0, arising from C–D coupling, instead of sharp peak at δ 71.3 in 13C NMR further confirmed the deuteration at the chlorine-attached carbon atom in 5n (Scheme 3). Further, in order to understand

Photochemical approach to functionalized benzobicyclo[3.2.1]octene structures via fused oxazoline derivatives from 4- and 5-(o-vinylstyryl)oxazoles

• Ivana Šagud,
• Simona Božić,
• Željko Marinić and
• Marija Šindler-Kulyk

Beilstein J. Org. Chem. 2014, 10, 2222–2229, doi:10.3762/bjoc.10.230

• the incorporation of deuterium in the bicyclo[3.2.1]octadiene moiety and a methoxy group on the N=C oxazoline bond by 1,4-addition or more likely by addition to the N=C bond followed by keto–enol tautomerization giving 14. The adducts are spectroscopically completely identified (see Supporting