Phosphodiester models for cleavage of nucleic acids

• Satu Mikkola,
• Tuomas Lönnberg and
• Harri Lönnberg

Beilstein J. Org. Chem. 2018, 14, 803–837, doi:10.3762/bjoc.14.68

• proceeds via a pentacoordinated species having the structure of a trigonal bipyramid. In case this species represents an energy maximum on a single barrier energy profile, as with SN2 displacement at carbon, the reaction is called concerted and the pentacoordinated species is a transition state. The

Enantioselective dioxytosylation of styrenes using lactate-based chiral hypervalent iodine(III)

• Morifumi Fujita,
• Koki Miura and
• Takashi Sugimura

Beilstein J. Org. Chem. 2018, 14, 659–663, doi:10.3762/bjoc.14.53

• proceed via an SN2 reaction of a cyclic intermediate such as I1, judging from the syn selectivity of the dioxytosylation [52][53]. The attack of the tosylate ion on I1 possibly takes place at the benzylic position or at the methylene carbon atom. The positive charge of I1 may be stabilized by the aryl

• styrene with 4a–e preferentially gave (S)-3, which forms via an electrophilic addition of the iodane toward the Si face of styrene, followed by an SN2 reaction with the tosylate ion. If an SN1 mechanism were involved in the oxytosylation of I1, the enantiomeric ratio of 3 would decrease owing to the

• planar structure of the benzylic cation. Thus, the tosylate ion may act as an effective nucleophile for the SN2 reaction of I1. The stereoface-differentiation in the dioxytosylation reaction using the lactate-derived aryl-λ3-iodanes is similar to that in preceding reactions [14], which include the

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

• alternative way to the desired amine 12a, based on the SN2 reaction of the activated alcohol 13 [34][35] with benzylamine, also failed (Scheme 2). The Mitsunobu approach to convert the hydroxy group into an amine function was also unsuccessful. Although 13 reacted with phthalimide gave the desired product 13a

High-yielding continuous-flow synthesis of antimalarial drug hydroxychloroquine

• Eric Yu,
• Hari P. R. Mangunuru,
• Nakul S. Telang,
• Caleb J. Kong,
• Jenson Verghese,
• Stanley E. Gilliland III,
• Saeed Ahmad,
• Raymond N. Dominey and
• B. Frank Gupton

Beilstein J. Org. Chem. 2018, 14, 583–592, doi:10.3762/bjoc.14.45

• significant opportunity for optimization. While the recent improved route (Scheme 1b) by Li and co-workers [21] eliminates the protection–deprotection steps, its use of a complex multi-transition-metal-catalyst system to achieve direct SN2 substitution of the chlorine on 3 by amine 7, is sub-optimal [22][23

Stereochemical outcomes of C–F activation reactions of benzyl fluoride

• Neil S. Keddie,
• Pier Alexandre Champagne,
• Justine Desroches,
• Jean-François Paquin and
• David O'Hagan

Beilstein J. Org. Chem. 2018, 14, 106–113, doi:10.3762/bjoc.14.6

• an enantiopure isotopomer of benzyl fluoride to identify whether the reaction conditions favour a dissociative (SN1) or associative (SN2) pathway. [2H]-Isotopomer ratios in the reactions were assayed using the Courtieu 2H NMR method in a chiral liquid crystal (poly-γ-benzyl-L-glutamate) matrix and

• substantial F···HOR hydrogen bond interactions, rather than through electrostatic stabilisation only [3]. This stabilisation was suggested to lead to a purely associative bimolecular (SN2) mechanism. The authors also studied the C–F activated Friedel–Crafts reactions [6][7] using very strong hydrogen bond

• benzylic carbocation and a formal equivalent of HF (which behaves in an autocatalytic manner as a stronger hydrogen bond donor than HFIP or TFA). Overall, there are three possible mechanistic pathways that these C–F activation reactions could follow: SN1, SN2, and a mixed SN1/SN2 pathway. Typically

Conformational preferences of α-fluoroketones may influence their reactivity

• Graham Pattison

Beilstein J. Org. Chem. 2017, 13, 2915–2921, doi:10.3762/bjoc.13.284

• ; Introduction α-Halogenated ketones are widely used electrophiles in organic synthesis, being highly reactive in both nucleophilic addition to the carbonyl group and in SN2 nucleophilic displacements [1]. Our research group has recently been exploring the synthesis and reactivity of α-fluorinated ketones [2][3

• electrophiles available to synthetic chemists for SN2 substitution [5]. The orbital overlap in α-halogenated ketones also provides activation to the carbonyl group, making it more reactive towards nucleophilic addition than non-halogenated carbonyl compounds [6]. However, relatively little work has been

Acid-catalyzed ring-opening reactions of a cyclopropanated 3-aza-2-oxabicyclo[2.2.1]hept-5-ene with alcohols

• Katrina Tait,
• Alysia Horvath,
• Nicolas Blanchard and
• William Tam

Beilstein J. Org. Chem. 2017, 13, 2888–2894, doi:10.3762/bjoc.13.281

• reactions. The scope of the reaction was successfully expanded to include primary, secondary, and tertiary alcohol nucleophiles. Through X-ray crystallography, the stereochemistry of the product was determined which confirmed an SN2-like mechanism to form the ring-opened product. Keywords: acid catalysis

• compound 19 for the cleavage of the C–O bond (b) (Scheme 4). We initially anticipated that the SN2’ type ring-opening would occur which would lead to the formation of ring-opened product 27 (Scheme 5). However, in all cases tested, only the SN2 type ring-opened product 26 was formed. Results and Discussion

• cleavage of the C–O bond as seen in path A, the free carbocation 28 would form in an SN1-like manner. The nucleophile could therefore attack from either the top or the bottom, forming products 26a and 29. Alternatively, in path B the oxygen atom could be protonated and undergo an SN2-like mechanism with

Recent progress in the racemic and enantioselective synthesis of monofluoroalkene-based dipeptide isosteres

• Myriam Drouin and
• Jean-François Paquin

Beilstein J. Org. Chem. 2017, 13, 2637–2658, doi:10.3762/bjoc.13.262

• =CH]-Gly isosteres, a SN2’ reaction upon 3,3-difluoropropene substrates can be used, as shown by Taguchi’s group. The synthesis of monofluoroalkenes starting from 3,3-difluoropropenes and using trialkylaluminium reagents was developed. Using this methodology, they were able to prepare Boc-Nva-ψ[CF=CH

• ]-Gly isostere [26] via a SN2’ reaction (Scheme 3). The defluorinative allylic alkylation of terminal 3,3-difluoropropene 10 with triethylaluminium selectively provided the corresponding (Z)-monofluoroalkene 11. In this case, the use of Et3Al allowed access to a norvaline (Nva) isostere. Then, alcohol

• reacted easily in a SN2 reaction to give a more functionalized molecule. For example, treatment of the chlorinated monofluoroalkene with NaN3 provided the corresponding N3-containing monofluoroalkene. The azide group underwent a 1,3-dipolar cycloaddition to give a 1,2,3-triazole, which is also a peptide

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

• could consist in a nucleophilic substitution (SN2) involving chloride ions as nucleophilic species to produce the intermediate II. Then, a repetition of this mechanism yields phosphonic acid. The preponderant route is likely governed by the stability of the carbocation and the steric hindrance around

• avoid side reactions (from SN1 or SN2 mechanism) [204] that can involve the functional groups present in the amino acid or peptide. These conditions were applied to prepare the compound 82 from 81 [205][206] (Figure 24). 4. From dichlorophosphine (R–PCl2) or dichlorophosphine oxide (R–P=OCl2) Aryl- and

Enzymatic synthesis of glycosides: from natural O- and N-glycosides to rare C- and S-glycosides

• Jihen Ati,
• Pierre Lafite and
• Richard Daniellou

Beilstein J. Org. Chem. 2017, 13, 1857–1865, doi:10.3762/bjoc.13.180

• sugar during GT-catalysed reactions, GTs are also classified as inverting or retaining (Figure 1). Inverting GTs operate via a SN2 mechanism in a single displacement step where an acid/base residue enhances the nucleophilicity of the acceptor, via an oxocarbenium-like transition state. Unlike inverting

• GTs, there is much controversy of the molecular mechanism of retaining GTs [13][14][15]. Retention of the anomeric carbon stereochemistry can occur either following a two-step displacement SN2 type mechanism (as in retaining GH), or via a “SNi-like” mechanism, that involves a front-side single

• nucleophilic attack of the acceptor, however, little information is known on the pathways involved in these reactions (SN2 or SNi-like), because of the few examples of such enzymes characterization in literature, when compared to canonical O- and N-GTs. S-Glycosyltransferases Few examples of natural S

Chiral phase-transfer catalysis in the asymmetric α-heterofunctionalization of prochiral nucleophiles

• Johannes Schörgenhumer,
• Maximilian Tiffner and
• Mario Waser

Beilstein J. Org. Chem. 2017, 13, 1753–1769, doi:10.3762/bjoc.13.170

• for further functionalizations by stereospecific nucleophilic SN2-type displacement reactions with different nucleophiles [66][85][86][87]. Accordingly, it comes as no surprise that their asymmetric synthesis has been intensively investigated in the past, either relying on asymmetric (transition

Mechanochemical N-alkylation of imides

• Anamarija Briš,
• Mateja Đud and
• Davor Margetić

Beilstein J. Org. Chem. 2017, 13, 1745–1752, doi:10.3762/bjoc.13.169

• a precedence in the application of weaker base in mechanochemical synthesis of triphenylphosphoranes [32]. Often DMF is used as solvent in imide alkylation reactions, which promotes SN2 reactions [33] and its low volatility is advantageous over more environmentally friendly solvents which might be

• . Computational section To elucidate reasons for the observed regioselectivities, the reactions of uracil and 7,8-dimethylalloxazine with benzylamine and ethyl bromide were studied by DFT calculations using the B3LYP/6-311+G**//B3LYP/6-31G*+ZPVE method. The transition-state calculations of the SN2 reaction of

Synthesis and metal binding properties of N-alkylcarboxyspiropyrans

• Alexis Perry and
• Christina J. Kousseff

Beilstein J. Org. Chem. 2017, 13, 1542–1550, doi:10.3762/bjoc.13.154

• mL) or the absence of polar aprotic solvent-mediated acceleration of this SN2 process (Table 1, compare entries 6, 7 and 8). The relative instability of indolium salts is well-documented [26] and our attempts to purify compounds 3 by silica gel chromatography or recrystallisation were unsuccessful

• -bromocarbonyls such as bromoacetic acid are excellent SN2 electrophiles, and N-alkylation of 2,3,3-trimethylindolenine (1) with bromoacetic acid (2a) was successful, if somewhat sluggish, at room temperature. Reaction of the crude indolium salt 3a with 3-methoxy-5-nitrosalicylaldehyde (5) was also conducted at

Strategies toward protecting group-free glycosylation through selective activation of the anomeric center

• A. Michael Downey and
• Michal Hocek

Beilstein J. Org. Chem. 2017, 13, 1239–1279, doi:10.3762/bjoc.13.123

• glycosylated with the opposite stereochemistry at the anomeric position to the donor in an SN2-like mechanism that is reasonably well understood. Retaining GTs provide glycosides with the same stereochemistry at the anomeric position as the donor. However, the mechanism(s) is less well understood and is still

• group contains two heteroatoms, X and Y that can be activated at the remote atom (Y) by an electrophilic species (H of an alcohol) or a metal cation resulting in a reactive intermediate. This complex could then undergo an SN2-like attack of a hydroxy group to furnish the glycoside with inversion of

• SN2-like reaction (Scheme 9). The most unfortunate drawbacks of the procedure include the need for a large excess of the alcohol acceptor and the multistep synthesis of the galactosyl donor. The synthesis of the monoprotected activated galactosyl donor requires the use of protecting groups, however

Substitution of fluorine in M[C₆F₅BF₃] with organolithium compounds: distinctions between O- and N-nucleophiles

• Anton Yu. Shabalin,
• Nicolay Yu. Adonin and
• Vadim V. Bardin

Beilstein J. Org. Chem. 2017, 13, 703–713, doi:10.3762/bjoc.13.69

• elimination of LiF. In contrary, the cation–anion bonds in O-nucleophiles and in N-nucleophiles are ionic (M = K, Na) and the fluoride affinities of K+ and Na+ are smaller than that of Li+. These factors determine the reaction route with K[C6F5BF3] by a simple SN2 mechanism. Preparation of

Fluorescent carbon dots from mono- and polysaccharides: synthesis, properties and applications

• Stephen Hill and
• M. Carmen Galan

Beilstein J. Org. Chem. 2017, 13, 675–693, doi:10.3762/bjoc.13.67

• , each CD sample was exposed to the same concentration (0.001 M) of divalent metal cations Cu2+, Cd2+, Sn2+ or Zn2+ in solution and the fluorescence response monitored. The starch-based S-CDs showed an interesting PL response, whereas the fluorescence output increased when in solution with all metal ions

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

• substituted carbocycles [119][120]. An example in described in Scheme 22. The 5-membered ring is formed via a K2CO3 mediated SN2 – conjugate addition sequence between malononitrile and 6-bromo-2-hexenoate derivatives 67a,b. Dicyanocyclopentanes 68a,b are treated with tributyltin hydride/AIBN giving the

Nucleophilic displacement reactions of 5′-derivatised nucleosides in a vibration ball mill

• Olga Eguaogie,
• Patrick F. Conlon,
• Francesco Ravalico,
• Jamie S. T. Sweet,
• Thomas B. Elder,
• Louis P. Conway,
• Marc E. Lennon,
• David R. W. Hodgson and
• Joseph S. Vyle

Beilstein J. Org. Chem. 2017, 13, 87–92, doi:10.3762/bjoc.13.11

• conditions) [16]. Following Sikchi and Hultin’s original description of nucleoside derivatisation in a low-energy, planetary ball mill [17], commercial, higher energy vibration mills have been used to facilitate established [18][19][20][21] and unprecedented [22] nucleoside transformations. Remarkably, SN2

First DMAP-mediated direct conversion of Morita–Baylis–Hillman alcohols into γ-ketoallylphosphonates: Synthesis of γ-aminoallylphosphonates

• Marwa Ayadi,
• Haitham Elleuch,
• Emmanuel Vrancken and
• Farhat Rezgui

Beilstein J. Org. Chem. 2016, 12, 2906–2915, doi:10.3762/bjoc.12.290

• corresponding SN2-type products 6a–d in 63 to 70% isolated yields. Alternatively, the alcohol 5 produced the corresponding acetate 7 which, mediated by Ce(III), was successfully converted into the corresponding γ-aminoallylphosphonates 8a–d. Keywords: allylic substitution; γ-aminoallylphosphonate; Arbuzov

• phosphites gave the corresponding phosphonates 4b and 4c in 60–62% yields. The reaction of secondary alcohols 3b and 3c with trialkyl phosphites was also surveyed. Under the previous reaction conditions (solvent-free, 80 °C, without any additive) an SN2’-type reaction followed by an Arbuzov rearrangement

Superelectrophilic activation of 5-hydroxymethylfurfural and 2,5-diformylfuran: organic synthesis based on biomass-derived products

• Dmitry S. Ryabukhin,
• Dmitry N. Zakusilo,
• Mikhail O. Kompanets,
• Anton A.Tarakanov,
• Irina A. Boyarskaya,
• Tatiana O. Artamonova,
• Mikhail A. Khohodorkovskiy,
• Iosyp O. Opeida and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2016, 12, 2125–2135, doi:10.3762/bjoc.12.202

• (Table 2), this reaction, most probably, proceeds through an SN2 pathway, where “pure” heteroaromatic cation B is not formed. At least the reaction may go through late transition state, in which the C–O bond in the CH2O+H2 group is rather elongated, resulting in a larger positive charge on this carbon

Synthesis of the C8’-epimeric thymine pyranosyl amino acid core of amipurimycin

• Pramod R. Markad,
• Navanath Kumbhar and
• Dilip D. Dhavale

Beilstein J. Org. Chem. 2016, 12, 1765–1771, doi:10.3762/bjoc.12.165

• orientation indicating 5’S absolute configuration as anticipated from the SAE mnemonic in compound 8. As the C5’ and C6’ stereocenters in 14 are derived from the regioselective SN2 opening of epoxide 8 by NaN3, the configuration at the C6’ (carrying azido group) was therefore assigned as 6’R. In the 1H NMR

TMSBr-mediated solvent- and work-up-free synthesis of α-2-deoxyglycosides from glycals

• Mei-Yuan Hsu,
• Yi-Pei Liu,
• Sarah Lam,
• Su-Ching Lin and
• Cheng-Chung Wang

Beilstein J. Org. Chem. 2016, 12, 1758–1764, doi:10.3762/bjoc.12.164

• pseudoequatorial position [78] and the ensuing SN2-like displacement by the alcohol contributes to the improvement of the α-selectivity (Scheme 2, route A). Alternatively, it is possible that a 2-deoxyglycosyl bromide is first generated mainly in the more stable α-form [61]. The glycosyl bromide intermediate then

• undergoes double SN2-like substitution by TPPO and the alcohol to give the α-glycoside as the major product [77] (Scheme 2, route B). Conclusion A simple, efficient, and environmentally friendly method for preparing S- and O-2-deoxyglycosides was established. S-2-Deoxyglycosides were obtained with moderate

Total synthesis of leopolic acid A, a natural 2,3-pyrrolidinedione with antimicrobial activity

• Atul A. Dhavan,
• Rahul D. Kaduskar,
• Loana Musso,
• Leonardo Scaglioni,
• Piera Anna Martino and
• Sabrina Dallavalle

Beilstein J. Org. Chem. 2016, 12, 1624–1628, doi:10.3762/bjoc.12.159

• assume that the reaction occurred via inversion of the configuration at the hydroxylated carbon, based on an intramolecular SN2 cyclocarbamation by the Boc group [20][21]. The small coupling constant (J = 2.6 Hz) between the two hydrogens on the oxazolidinone ring confirmed that the compound was the anti

One-pot synthesis of 4′-alkyl-4-cyanobiaryls on the basis of the terephthalonitrile dianion and neutral aromatic nitrile cross-coupling

• Roman Yu. Peshkov,
• Elena V. Panteleeva,
• Wang Chunyan,
• Evgeny V. Tretyakov and
• Vitalij D. Shteingarts

Beilstein J. Org. Chem. 2016, 12, 1577–1584, doi:10.3762/bjoc.12.153

• -regioselectivity of the bulylation of monoanion 3i is typical for an alkylation with primary alkyl halides of cyanocyclohexadienyl anions derived by two-electron reduction of aromatic mononitriles in liquid ammonia, which was studied earlier and was found to proceed via an SN2 mechanism [26][35]. Conclusion We

Dinuclear thiazolylidene copper complex as highly active catalyst for azid–alkyne cycloadditions

• Anne L. Schöffler,
• Ata Makarem,
• Frank Rominger and
• Bernd F. Straub

Beilstein J. Org. Chem. 2016, 12, 1566–1572, doi:10.3762/bjoc.12.151

• less time-consuming and more cost-efficient synthesis. Commercially available, inexpensive 4,5-dimethylthiazole is used as azole starting material instead of 4-aryl-1,2,4-triazoles. The precursor 1a for the NHC ancillary ligand is synthesized via a double SN2-reaction of two equivalents of thiazole