Catalyst-Free Transfer Hydrogenation of Activated Alkenes Exploiting Isopropanol as the Sole and Traceless Reductant.

Both metal-catalyzed and organocatalytic transfer hydrogenation reactions are widely employed for the reduction of C=O and C=N bonds. However, selective transfer hydrogenation reactions of C=C bonds remain challenging. Therefore, the chemoselective transfer hydrogenation of olefins under mild conditions and in the absence of metal catalysts, using readily available and inexpensive reducing agents (i.e. primary and secondary alcohols), will mark a significant advancement towards the development of green transfer hydrogenation strategies. Described herein is an unconventional catalyst-free transfer hydrogenation reaction of activated alkenes using isopropanol as an eco-friendly reductant and solvent. The reaction gives convenient synthetic access to a wide range of substituted malonic acid half oxyesters (SMAHOs) in moderate to good yields. Mechanistic investigations point towards an unprecedented hydrogen bond-assisted transfer hydrogenation process.

Diisopropyl 2-[(4-nitro-benzo-yl)amino]-propane-dioate.

The title compound, C16H20N2O7, crystallizes in the space group C2 with two mol-ecules in the asymmetric unit. The crystal packing shows O⋯π inter-actions between the two mol-ecules.

Benzyl-hexa-decyl-dimethyl-ammonium chloride dihydrate.

The title compound, C25H46N+·Cl-·2H2O, crystallizes in the space group P21 with one organic mol-ecule in the asymmetric unit. The compound belongs to a class of benzalkonium chlorides (BACs) with an alkyl chain length of 16 carbon atoms in an all-trans conformation.

Crystal structure and DFT calculations of Cp2NbH(SiIMe2)(SiFMe2): an asymmetric bis(silyl) niobocene hydride complex.

An asymmetric bis(silyl) niobocene hydride complex, namely, bis(η5-cyclopentadienyl)(fluorodimethylsilyl)hydrido(iododimethylsilyl)niobium, [Nb(C5H5)2(C2H6FSi)(C2H6ISi)H] or Cp2NbH(SiIMe2)(SiFMe2), has been studied to determine the effect of the silyl ligand on the position of the hydride attached to the Nb atom. It has been shown that when a Group 17 atom is substituted onto one of the silyl ligands, there is a greater interaction between the hydride and this ligand, as demonstrated by a shorter Si...H distance. In the present work, we have investigated the effect when the silyl ligands are substituted by different Group 17 atoms. We present here the structure and DFT calculations of Cp2NbH(SiIMe2)(SiFMe2), showing that the position of the hydride is located between the two silyl ligands. The results from our investigation show that the hydride is closer to the silyl ligand that is substituted by fluorine.

Intramolecular N-Me and N-H aminoetherification for the synthesis of N-unprotected 3-amino-O-heterocycles.

A mild Rh-catalyzed method for synthesis of cyclic unprotected N-Me and N-H 2,3-aminoethers using an olefin aziridination-aziridine ring-opening domino reaction has been developed. The method is readily applicable to the stereocontrolled synthesis of a variety of 2,3-disubstituted aminoether O-heterocyclic scaffolds, including tetrahydrofurans, tetrahydropyrans and chromanes.

Total Synthesis of the Nagelamides - Synthetic Studies toward the Reported Structure of Nagelamide D and Nagelamide E Framework.

The nagelamides are a small subset of the oroidin family of marine sponge-derived alkaloids and are, for the most part, dimeric in nature. As part of our efforts to develop synthetic access to this family, a Stille cross-coupling strategy is used to construct the bis-imidazolyl core skeleton. Reduction of the bis-vinylimidazole delivered the core framework of nagelamide D. Introduction of the 2-amino groups via the corresponding azides and introduction of the pyrrolecarboxamides through a double Mitsunobu reaction using a pyrrole hydantoin provided the putative structure of nagelamide D. The spectroscopic data for the synthetic and sponge-derived materials did not match well, whereas the spectroscopic data were a good match for closely related oroidin alkaloids, supporting the structure of the synthetic material. The structure of the synthetic material was further corroborated by obtaining an X-ray crystal structure of a derivative. Electrocyclization of an advanced precursor affords a dihydrobenzimidazole, which is expected to serve as a key intermediate en route to nagelamide E and ageliferin.

Total synthesis of isatindigotindoline C.

Total synthesis of isatindigotindoline C, a 3,3'-spiropyrrolidine oxindole alkaloid, is achieved in two steps using an exo-selective decarboxylative 1,3-dipolar cycloaddition as the key step. The synthesis verifies the originally assigned relative anti-stereochemistry for the bis-oxindole core of isatindigotindoline C.

Arylboronic Acid-Catalyzed C-Allylation of Unprotected Oximes: Total Synthesis of N-Me-Euphococcine.

O-Unprotected keto- and aldoximes are readily C-allylated with allyl diisopropyl boronate in the presence of arylboronic acid catalysts to yield highly substituted N-α-secondary and tertiary homoallylic hydroxylamines. The method was used in the total synthesis of the trace alkaloid N-Me-Euphococcine.

[4-(4-Meth-oxy-phen-yl)-8-oxo-3-(phenyl-selan-yl)spiro-[4.5]deca-3,6,9-trien-2-yl]methyl-cyanamide.

The title compound, C25H22N2O2Se, crystallizes in the space group P21/c with one mol-ecule in the asymmetric unit. The compound was synthesized by the addition of phenyl-selenyl bromide to a cyanamide. The phenyl-selenyl portion and the cyano group, as well as the ketone functional group in the cyclo-hexa-2,5-dien-1-one portion of the structure, are disordered, with occupancy factors of 0.555 (14) and 0.445 (14).

Organic Azide and Auxiliary-Ligand-Free Complexes of Coinage Metals Supported by N-Heterocyclic Carbenes.

Organic azide complexes of copper(I) and silver(I), [(SIPr)CuN(1-Ad)NN][SbF6], [(SIPr)CuN(2-Ad)NN][SbF6], [(SIPr)CuN(Cy)NN][SbF6], and [(SIPr)AgN(1-Ad)NN][SbF6] have been synthesized by using Ag[SbF6] and the corresponding organic azides with (SIPr)CuBr and (SIPr)AgCl (SIPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene). The copper and silver organic azide complexes were characterized by various spectroscopic techniques and X-ray crystallography. Group trends of isoleptic Cu(I), Ag(I), and Au(I) organic azide complexes are presented on the basis of experimental data and a detailed computational study. The νasym(N3) values of the metal-bound 1-AdNNN in [(SIPr)MN(1-Ad)NN]+ follow the order Ag < Cu < Au. DFT calculations show that gold(I) forms the strongest bond with 1-AdNNN in this series, while silver has the weakest interaction. Furthermore, auxiliary ligand free coinage metal N-heterocyclic carbene complexes, [(SIPr)M][SbF6], have been synthesized via metathesis reactions of (SIPr)MCl (M = Cu, Ag, Au) with Ag[SbF6]. X-ray crystal structures of dinuclear [(SIPr)Ag]2[SbF6]2 and [(SIPr)Au]2[SbF6]2 are also reported. They show close metallophilic contacts. [(SIPr)Au]2[SbF6]2 reacts with OEt2, SMe2, and CNtBu to afford [(SIPr)Au(OEt2)][SbF6], [(SIPr)Au(SMe2)][SbF6], and [(SIPr)Au(CNtBu)][SbF6] adducts, respectively.

Titanium-Mediated Synthesis of Spirocyclic NH-Azetidines from Oxime Ethers.

The TiIV -mediated synthesis of spirocyclic NH-azetidines from oxime ethers using either an alkyl Grignard reagent or terminal olefin ligand exchange coupling partner is described. Through a proposed Kulinkovich-type mechanism, a titanacyclopropane intermediate forms and serves as a 1,2-aliphatic dianion equivalent, inserting into the 1,2-dielectrophilc oxime ether to ultimately give rise to the desired N-heterocyclic four-membered ring. This transformation proceeds in moderate yield to furnish previously unreported and structurally diverse NH-azetidines in a single step.

Crystal structures of 4-{(E)-3-[(imino-λ5-aza-nyl-idene)amino]-prop-1-en-yl}-N,N-di-methyl-imidazole-1-sulfonamide and 2-[(imino-λ5-aza-nyl-idene)amino]-4-{(E)-3-[(imino-λ5-aza-nyl-idene)amino]-prop-1-en-yl}-N,N-di-methyl-imidazole-1-sulfonamide.

The structures of two azide containing imidazole derivatives are reported. Allylic azides are fairly reactive making them attractive starting compounds to convert into amides. The first, C8H12N6O2S, contains one azide group with an Nα-Nß distance of 1.229 (2) Šand an Nß-Nγ distance of 1.128 (2) Å. The second, C8H11N9O2S, contains two azide groups with an average Nα-Nß distance of 1.249 (2) Šand an average Nß-Nγ distance of 1.132 (2) Å. Each compound contains a bulky protecting group (di-methyl-amino-sulfon-yl) which can be easily removed under mildly acidic conditions.

Synthesis of Structurally Diverse 3-, 4-, 5-, and 6-Membered Heterocycles from Diisopropyl Iminomalonates and Soft C-Nucleophiles.

Herein, we present a general synthetic strategy for the preparation of 3-, 4-, 5-, and 6-membered heterocyclic unnatural amino acid derivatives by exploiting facile Mannich-type reactions between readily available N-alkyl- and N-aryl-substituted diisopropyl iminomalonates and a wide range of soft anionic C-nucleophiles without using any catalyst or additive. Fully substituted aziridines were obtained in a single step when enolates of α-bromo esters were employed as nucleophiles. Enantiomerically enriched azetidines, γ-lactones, and tetrahydroquinolines were obtained via a two-step catalytic asymmetric reduction and cyclization sequence from ketone enolate-derived adducts. Finally, highly substituted γ-lactams were prepared in one pot from adducts obtained using acetonitrile-derived carbanions. Overall, this work clearly demonstrates the utility of iminomalonates as highly versatile building blocks for the practical and scalable synthesis of structurally diverse heterocycles.

A new 3D luminescent Zn(ii)-organic framework containing a quinoline-2,6-dicarboxylate linker for the highly selective sensing of Fe(iii) ions.

A new 3D zinc-organic framework [Zn(QDA)]·0.5H2O·0.7DMF (1, H2QDA = quinoline-2,6-dicarboxylic acid, DMF = N,N-dimethylformamide) was synthesized under solvothermal conditions. The single crystal X-ray diffraction analysis reveals that the 3D framework structure of 1 has a PtS topology and contains Zn(ii) ions having distorted square pyramidal geometry with ZnO4N configuration. The phase purity of the bulk sample was characterized by X-ray powder diffraction (XRPD), thermogravimetric analysis (TGA) and Fourier transform infrared (FT-IR) spectroscopy. The as-synthesized sample (1) was activated by stirring with acetone for 24 h, followed by heating under vacuum for 24 h at 120 °C. The TGA experiment indicated that both 1 and its activated form (1') are stable up to 380 °C. The crystalline structure of the compound was retained after immersion in water, 1 M HCl, acetic acid and NaOH (at pH = 10) solutions. Compound 1' exhibited very quick fluorescence quenching response after the addition of Fe3+ solution. This quenching was not affected by the presence of other competitive metal cations. A very low detection limit of 9.2 ppb was observed for Fe3+ ions, which is among the lowest values documented in the literature for MOF based fluorescent probes. Both fluorescence resonance energy transfer (FRET) and photo-induced electron transfer (PET) processes play major roles in the selective detection of Fe3+ ions. The recyclability experiment suggested that 1' can be used for the long-term detection of Fe3+ ions.

Transition metal-free direct dehydrogenative arylation of activated C(sp3)-H bonds: synthetic ambit and DFT reactivity predictions.

A transition metal-free dehydrogenative method for the direct mono-arylation of a wide range of activated C(sp3)-H bonds has been developed. This operationally simple and environmentally friendly aerobic arylation uses tert-BuOK as the base and nitroarenes as electrophiles to prepare up to gram quantities of structurally diverse sets (>60 examples) of α-arylated esters, amides, nitriles, sulfones and triaryl methanes. DFT calculations provided a predictive model, which states that substrates containing a C(sp3)-H bond with a sufficiently low pK a value should readily undergo arylation. The DFT prediction was confirmed through experimental testing of nearly a dozen substrates containing activated C(sp3)-H bonds. This arylation method was also used in a one-pot protocol to synthesize over twenty compounds containing all-carbon quaternary centers.

Intramolecular Diels-Alder Reaction of a Silyl-Substituted Vinylimidazole en Route to the Fully Substituted Cyclopentane Core of Oroidin Dimers.

An intramolecular Diels-Alder reaction of a silyl-substituted vinylimidazole delivers a diastereomeric mixture of C4-silyl functionalized dihydrobenzimidazoles. Subsequent diastereoselective reduction and elaboration of the lactone gives rise to a polysubstituted tetrahydrobenzimidazole, which, upon oxidative rearrangement, affords a single spirofused imidazolone containing all of the relevant functionality for an approach to the oroidin dimers axinellamine, massadine, and palau'amine.

Catalyst-Controlled Diastereoselective Synthesis of Cyclic Amines via C-H Functionalization.

Reliable regio- and stereochemical techniques applicable to nonactivated aliphatic systems remain largely elusive due to the challenges of discriminating between multiple, relatively strong sp3 C-H bonds whose chemical behavior often differ only subtly. Nevertheless, approaches that employ directing groups and/or auxiliaries have emerged, but impose practical restrictions, especially in complex molecule synthesis. This report describes a catalyst-controlled regio- and diastereoselective synthesis of N-unprotected pyrrolidines via dirhodium catalyzed intramolecular nitrene insertion into sp3 C-H bonds. The reaction proceeds at rt without external oxidants, nitrene stabilizing groups, or directing functionality. The insights that emerged from the conformational/stereoselectivity relationships (CSR) between catalysts and substrates provide a framework for rational catalyst design that can accommodate a broader range of aliphatic C-H chemistry.

Tandem Oxidative Dearomatizing Spirocyclizations of Propargyl Guanidines and Ureas.

Treatment of propargyl ureas or guanidines with iodosobenzene diacetate results in an oxidative tandem amination/etherification dearomatizing spirocyclization. This transformation leads directly to the complete framework of the Leucetta alkaloids, spirocalcaridine A and B.