Vicinal Bis(methylene) Heterocyclic Diene in Natural Product Synthesis: A Convergent Biomimetic Total Synthesis of Prunolactone A.

The first total syntheses of the natural isocoumarin prunolactone A with a 6/6/6/6/6 spiropentacyclic skeleton and its unnatural (3')-epimer in 10 and 8 steps, respectively, are reported. The syntheses feature generation of a reactive 3,4-bis(methylene)isocoumarin intermediate, its biomimetic Diels-Alder reactions with the shikimic-acid-derived scytolide and (8)-scytolide, and a Mitsunobu reaction allowing access to scytolide in a stereochemically pure form. Computational support for the selectivity of the Diels-Alder reaction is provided.

Ruthenium Complexes with N-Bound 2-Pyridonato Ligand as O-Donors: A New Synthetic Approach and the Effect on Reactivity.

In this study, Ru complexes [(η-p-cymene)RuX(2-{(2,6-iPr-CH)N=CH}-CHN-6-(O))] (3: X=Cl; 4: X=I) were prepared with N-bound 2-pyridonato ligand by thermal base-free MeX elimination from ionic N,N-chelated Ru complexes [(η-p-cymene)RuX(κ-L)](X) (1: X=Cl; 2: X=I; L={2-[(2,6-iPr-CH)N=CH]-6-(OMe)CHN}). The Ru complex 3 was used as O-donor for Lewis (LA) or Brönsted acids. The reactions of 3 with SnCl, PhSnCl, ZnCl or HCl provided [(η-p-cymene)Ru(SnCl)(2-{(2,6-iPr-CH)N=CH}-CHN-6-(O→SnCl)] (6), [(η-p-cymene)RuCl(2-{(2,6-iPr-CH)N=CH}-CHN-6-(O→SnPhCl)] (7), and [(η-p-cymene)RuCl(2-{(2,6-iPr-CH)N=CH}-CHN-6-(O→)](μ-ZnCl) (8) and [(η-p-cymene)RuCl(2-{(2,6-iPr-CH)N=CH}-CHN-6-(OH)}](Cl) (9).

B-substituted group 1 phosphides: synthesis and reactivity.

1-Boryl-8-phosphinonaphthalenes 1-BCy-8-PCl-CH (1) and 1-BCy-8-PPhCl-CH (2) were prepared and used as starting materials for the synthesis of B-substituted phosphides. The reduction of 1 and 2 by Mg provided neutral compounds [1-BCy-8-PCy-CH] (3) and [1-BCy-8-PPh-CH] (4). Compound 3 represents the dimer of phosphinoborane 1-BCy-8-PCy-CH while complex 4 is a rare example of a discrete B ← P coordinated diphosphine.

Synthesis and reactivity of alkali metal aluminates bearing bis(organoamido)phosphane ligand.

In this study, we report a group of alkali metal aluminates bearing bis(organoamido)phosphane ligand. The starting complex {[PhP(NBu)]AlMe}Li·OEt (1) was prepared by stepwise deprotonation of the parent PhP(NHBu) by BuLi and AlMe. Further derivatization of aluminate 1 was performed by the virtual substitution of lithium -{[PhP(NBu)]AlMe}K (2), methyl substituents - {[PhP(NBu)]AlH}Li·THF (3), modification of steric bulk and induction effects on the phosphorus atom - {[BuP(-2,6-iPrCH)]AlMe}Li·(OEt) (4), and phosphorus atom oxidation state {[Ph(Y)P(NBu)]AlMe}Li (Y = O (5), S (6), Se (7), Te (8)).

Tin(II) cations stabilized by non-symmetric N,N',O-chelating ligands: synthesis and stability.

A series of novel non-symmetric neutral N,N',O-chelating ligands derived from the α-iminopyridine 2-(C(R)N(CH-2,6-iPr))-6-(RRPO)CHN (L1: R = H, R = R = Ph; L2: R = Me, R = R = Ph; L3: R = H; R = Ph, R = EtO; L4: R = Me, R = Ph, R = EtO; L5: R = H, R = R = iPrO; L6: R1 = Me, R = R = iPrO) were synthesized. Ligands L1-6 were reacted with SnCl and Sn(OTf) with the aim of studying the influence of different RRPO functional groups on the Lewis base mediated ionization of SnCl and Sn(OTf). While all ligands L1-6 provided the corresponding ionic tin(II) complexes [L1-6 → SnCl][SnCl] (1-6), only ligands L1, L4 and L6 were able to stabilize tin(II) dications [L1,4,6 → Sn(HO)][OTf] (7-9).

Lithium, Magnesium, and Zinc Centers N,N'-Chelated by an Amine-Amide Hybrid Ligand.

The synthesis and structure of lithium, magnesium, and zinc complexes ,'-chelated by a hybrid amine-amido ligand ([2-(MeNCH)CHNR], abbreviated as LR, where R = H, SiMe, or Bn) are reported. The reaction of the least sterically demanding LH with various magnesium sources gives the hexameric imide [LMg] () by the elimination of -butane from LHMgBu () or by the reaction of LHLi () with MeMgBr. [LH]Mg () is obtained through the addition of 0.

Ferrocene donor linked to pyridine/pyridinium acceptor a systematically enlarged π-linker.

Nine chromophores with ferrocene donor and pyridine/pyridinium acceptors have been prepared and further investigated. The performed X-ray analysis showed partially polarized and geometrically oblate pyridine unit. An extension of the π-system and -quaternization were revealed as suitable tools for exclusive manipulation of the LUMO with the almost steady HOMO.

Structurally rigidified cobalt bis(dicarbollide) derivatives, a chiral platform for labelling of biomolecules and new materials.

We report the difunctional modification of an anionic cobalta bis(dicarbollide)(1-) cluster with a B(8,8')-oxygen bridging unit that provides structural rigidity and an organic alkylazide substituent(s) on the carbon atoms of the metallacarborane cage. These ions present a good binding motif for incorporation into organic molecules using Huisgen-Sharpless (2+3) cycloaddition reactions. In addition, the compounds are chiral, as verified by separation of enantiomers using HPLC on chiral stationary phases (CSPs) and provide a high electrochemical peak in the window located outside of typical signals of biomolecules.

Reversible addition of tin(II) amides to nitriles.

Lappert's stannylene (Sn[N(SiMe)]) has been reacted with various nitriles, dinitriles and trinitriles with the formation of heteroleptic amidotin(II) amidinates of the general formulae [RC(NSiMe)]SnN(SiMe), R'{[C(NSiMe)]SnN(SiMe)} and R''{[C(NSiMe)]SnN(SiMe)}, where R = Ph (1), 2-(CN)-CH (2), 3-(CN)-CH (3); R' = 1,3-CH (4), 1,4-CH (5) and R'' = 1,3,5-CH (6). The reactions of amidotin(II) benzamidinate 1 with an excess of benzonitrile proceed to homoleptic tin(II) bis(benzamidinate) [PhC(NSiMe)]Sn, which reversibly eliminates benzonitrile and 1 when warmed. The premise of reversibility has been supported by a multinuclear time-dependent NMR study and a theoretical (DFT) description.

N-Donor stabilized tin(II) cations as efficient ROP catalysts for the synthesis of linear and star-shaped PLAs the activated monomer mechanism.

α-Iminopyridine ligands L (2-(CHN(CH-2,4,6-Ph))CHN), L (2-(CHN(CH-2,4,6-Bu))CHN) and L (1,2-(CHN-2-CHN)CHCH) differing by the steric demand of the substituent on the imine CHN group and by the number of donating nitrogen atoms were utilized to initiate a Lewis base mediated ionization of SnCl in an effort to prepare ionic tin(II) species [L → SnCl][SnCl]. The reaction of L and L with SnCl led to the formation of neutral adducts [L → SnCl] (2) and [L → SnCl] (3). The preparation of the desired ionic compounds was achieved by subsequent reactions of 2 and 3 with an equivalent of SnCl or GaCl.

Access to cationic polyhedral carboranes via dynamic cage surgery with N-heterocyclic carbenes.

Polyhedral boranes and heteroboranes appear almost exclusively as neutral or anionic species, while the cationic ones are protonated at exoskeletal heteroatoms or they are instable. Here we report the reactivity of 10-vertex closo-dicarbadecaboranes with one or two equivalents of N-heterocyclic carbene to 10-vertex nido mono- and/or bis-carbene adducts, respectively. These complexes easily undergo a reaction with HCl to give cages of stable and water soluble 10-vertex nido-type cations with protonation in the form of a BHB bridge or 10-vertex closo-type cations containing one carbene ligand when originating from closo-1,10-dicarbadecaborane.

Thiaborane Icosahedral Barrier Increased by the Functionalization of all Terminal Hydrogens in -1-SBH.

The electrophilic substitution of icosahedral 1-SBH with methyl iodide has resulted in two B-functionalized thiaboranes, 7,12-I-2,3,4,5,6,8,9,10,11-(CH)-1--SB and 7,8,12-I-2,3,4,5,6,9,10,11-(CH)--1-SB, with the former being significantly predominant. These two icosahedral thiaboranes are the first cases of polysubstituted polyhedral boron clusters with another vertex that differs from B and C. Such polyfunctionalizations have increased the earlier observed thiaborane icosahedral barrier, not exhibiting any reactivity toward bases, unlike the parent thiaborane.

Oxidative addition of cyanogen bromide to ,-chelated and Lappert's stannylenes.

Stannylenes of L2Sn type bearing either C,N-chelating (1, L = LCN = 2-(N,N-dimethylaminomethyl)phenyl) or bulky amido (2, L = LN = N(SiMe3)2) ligands react with cyanogen bromide (Br-C[triple bond, length as m-dash]N) via an oxidative-addition reaction to give monomeric six-coordinate (LCN)2Sn(Br)CN (1a) and four-coordinate (LN)2Sn(Br)CN (2a) stannanes in moderate yields. In solution, both 1a and 2a undergo instantaneous bromido-cyanido ligand redistribution reactions, leading to mixtures containing 1a, (LCN)2SnBr2 (1b) and (LCN)2Sn(CN)2 (1c) or 2a, (LN)2SnBr2 (2b) and (LN)2Sn(CN)2 (2c), respectively. The prepared species were characterised by multinuclear NMR spectroscopy in solution (1a-c and 2a-c) and in the solid state (1a-c).

Transformation of various multicenter bondings within bicapped-square antiprismatic motifs: -rearrangement.

Reported herein are mutual rearrangements in the whole series of seven bicapped-square antiprismatic -CBH by means of high-quality computations that disprove the earlier postulated (diamond-square-diamond) scheme for these isomerizations. The experimentally existing -1,2-CBH was able to be converted to 1,6-, and 1,10-isomers by pyrolysis, and the (diamond-square-diamond) mechanism was offered as an explanation of these processes. However, these computations disprove the postulated scheme for these isomerizations that take place in the ten-vertex series.

Cobalt Bis(dicarbollide) Alkylsulfonamides: Potent and Highly Selective Inhibitors of Tumor Specific Carbonic Anhydrase IX.

Invited for this month's cover is a collaboration from three institutes from the Czech Academy of Sciences: Institute of Inorganic Chemistry, Institute of Organic Chemistry and Biochemistry, and Institute of Molecular Genetics, and the University of Pardubice. The cover picture shows a family of potent and selective CA IX inhibitors that combines the structural motif of a bulky inorganic cobalt bis(dicarbollide) polyhedral ion with a propylsulfonamido anchor group. Read the full text of the article at 10.

Tetrazole Ring Substitution at Carbon and Boron Sites of the Cobalt Bis(dicarbollide) Ion Available via Dipolar Cycloadditions.

Herein, we describe the synthesis of two families of compounds accessible from [3 + 2] cycloaddition reactions of known B8-substituted isonitrilium and new C1-alkylnitrile and C(1,1')-dialkylnitrile derivatives of the [(1,2-CBH)-3,3'-Co(III)] ion with an azide ion that produce a tetrazole ring substitution at the cobaltacarborane cage. In addition, we outline the important differences in reactivity observed for the two types [B-isonitrilium/C-(alkyl)nitrile] of cobaltacarborane derivatives. The first family of compounds described corresponds to C5-atom-boronated tetrazole rings, with the five-membered moiety in the second type being doubly substituted at the N1 and C5 positions.

Cobalt Bis(dicarbollide) Alkylsulfonamides: Potent and Highly Selective Inhibitors of Tumor Specific Carbonic Anhydrase IX.

Carbonic anhydrase IX (CAIX) is an enzyme expressed on the surface of cells in hypoxic tumors. It plays a role in regulation of tumor pH and promotes thus tumor cell survival and occurrence of metastases. Here, derivatives of the cobalt bis(dicarbollide)(1-) anion are reported that are based on substitution at the carbon sites of the polyhedra by two alkylsulfonamide groups differing in the length of the aliphatic connector (from C1 to C4, n=1-4), which were prepared by cobalt insertion into the 7-sulfonamidoalkyl-7,8-dicarba-nido-undecaborate ions.

Direct Introduction of an Alkylsulfonamido Group on C-sites of Isomeric Dicarba-closo-dodecaboranes: The Influence of Stereochemistry on Inhibitory Activity against the Cancer-Associated Carbonic Anhydrase IX Isoenzyme.

Carbonic anhydrase IX (CA IX), a tumor-associated metalloenzyme, represents a validated target for cancer therapy and diagnostics. Herein, we report the inhibition properties of isomeric families of sulfonamidopropyl-dicarba-closo-dodecaboranes group(s) prepared using a new direct five-step synthesis from the corresponding parent cages. The protocol offers a reliable solution for synthesis of singly and doubly substituted dicarba-closo-dodecaboranes with a different geometric position of carbon atoms.

Electrophilic Methylation of Decaborane(14): Selective Synthesis of Tetramethylated and Heptamethylated Decaboranes and Their Conjugated Bases.

The paper reports specific syntheses of methylated decaborane(14), -BH (), derivatives. The reaction of with an excess of neat MeI and AlCl yields 1,2,3,4-Me--BH () essentially quantitatively when performed at room temperature. Heating the same mixture to 120 °C provides 1-I-2,3,4,5,7,8,10-Me--BH ().

Lithium and Dilithium Guanidinates, a Starter Kit for Metal Complexes Containing Various Mono- and Dianionic Ligands.

Comparative studies of the synthesis of lithium guanidinates via nucleophilic addition of lithium amides to carbodiimides were performed. Four combinations of small or sterically crowded carbodiimide and sterically crowded lithium amide or lithium amide containing an adjacent amino donor group give ten different types of complexes. In particular, 2,6-[(CH)CH]CHNHLi (DipNHLi, ) reacts with (CH)CHN═C═NCH(CH) upon the formation of the dissymmetric dimeric complex with four-coordinate Li atoms.

Experimental and Theoretical Evidence of Spin-Orbit Heavy Atom on the Light Atom H NMR Chemical Shifts Induced through H⋅⋅⋅I Hydrogen Bond.

Invited for the cover of this issue is the group of Michal Straka and Martin Dračínský (IOCB Prague, Czech Academy of Sciences). The image depicts a neutron star, which is used to represent the relativistic effects between a heavy element and a hydrogen atom reported in this work. Read the full text of the article at 10.

Experimental and Theoretical Evidence of Spin-Orbit Heavy Atom on the Light Atom H NMR Chemical Shifts Induced through H⋅⋅⋅I Hydrogen Bond.

Spin-orbit (SO) heavy-atom on the light-atom (SO-HALA) effect is the largest relativistic effect caused by a heavy atom on its light-atom neighbors, leading, for example, to unexpected NMR chemical shifts of H, C, and N nuclei. In this study, a combined experimental and theoretical evidence for the SO-HALA effect transmitted through hydrogen bond is presented. Solid-state NMR data for a series of 4-dimethylaminopyridine salts containing I , Br and Cl counter ions were obtained experimentally and by theoretical calculations.

The Influence of Halogenated Hypercarbon on Crystal Packing in the Series of 1-Ph-2-X-1,2-dicarba--dodecaboranes (X = F, Cl, Br, I).

Although 1-Ph2-X--1,2-CBH (X = F, Cl, Br, I) derivatives had been computed to have positive values of the heat of formation, it was possible to prepare them. The corresponding solid-state structures were computationally analyzed. Electrostatic potential computations indicated the presence of highly positive σ-holes in the case of heavy halogens.