Hexahydro-3-alkyl-3H-oxazolo[3,4-a]pyridines 4-15 for the quantitative analysis of various aldehydes were obtained in good yield via the condensation reaction of 2-hydroxymethylpiperidine (2-HMP) with aldehydes under mild conditions. When acrolein is used, the bicyclic 17 was obtained. This novel compound has suitable physical characteristic for an analytical standard. The hexahydro-3-vinyl-3H-oxazolo[3,4-a]pyridine 16 can be achieve at higher temperature. Using specific conditions, a diastereomeric mixture of 18/19 and pure 18, which are both bisadducts of 2-HMP with acrolein, can be obtained. Mechanistically, a thorough 1H-NMR study did not show any evidence that the condensation reaction proceeded via an enamine. The reaction probably proceeds through an elusive hemiaminal and fleeting iminium ion, which underwent subsequent cyclisation to gave hexahydro-3-alkyl-3H-oxazolo[3,4-a]pyridines 4-16. The reaction pathways for the preparation of 4-18 are described.

Optimized synthetic procedures for pyridinium ions featuring iminophosphorano (-N=PR3; R=Ph, Cy) pi-donor substituents in the 2- and 4- positions are described. Crystallographic and theoretical studies reveal that the strongly donating substituents severely polarize the pi-electrons of the pyridyl ring at the expense of aromaticity. Moreover, the pyridinium ions are readily deprotonated to generate powerful bispyridinylidene (BPY) organic electron donors. Electrochemical studies show exceptionally low redox potentials for the two-electron BPY/BPY2+ couples, ranging from -1.71 V vs the saturated calomel electrode for 3PhPh (with four Ph3P=N- groups) to -1.85 V for 3CyCy (with four Cy3P=N- groups). These new compounds represent the most reducing neutral organic electron donors (OEDs) currently known. Some preliminary reductions involving 3CyCy showed enhanced capability owing to its low redox potential, such as the thermally activated reduction of an aryl chloride, but purification challenges were often encountered.

Bispyridinylidenes (BPYs) have emerged as an important class of neutral organic electron donors, with redox potentials that vary widely with choice of substituent. Methods to predict the effect of substitution on the redox potential are therefore highly desirable. Here we show that the redox potential of BPYs featuring iminophosphorano substituents (R3P=N-), which represent the most reducing class of BPYs, can be predicted based on the well-known Tolman electronic parameter (TEP) for the respective phosphine fragment (R3P). Moreover, building on earlier work relating redox potentials to Hammett-type substituent constants, it is now possible to quantitatively predict sigma(+)(p) values for iminophosphorano substituents from TEP values. These results provide a path for precisely tailoring redox potentials of iminophosphorano-substituted BPYs, but also give quantitative descriptors for how these highly versatile iminophosphorano substituents can impact the properties of any molecular scaffold.

A meroterpenoid, guanahanolide A (1), was purified from a fermentation extract of Streptomyces sp. RKBH-B7. The planar structure of guanahanolide A (1) was elucidated by NMR spectroscopy, revealing a meroterpenoid comprised of an unprecedented sesterterpene skeleton. Upon determination of the relative configuration of 1 through X-ray crystallography, its absolute configuration was unambiguously assigned using Mosher ester analysis. Guanahanolide A (1) showed moderate cytotoxicity against human cancer cell lines MCF-7, HTB-26, and HCT-116.

A pathway to a range of diverse heterocycles was developed using a nucleophilic cyclization strategy. Lactams and ene-imines are accessed in a few steps from a common precursor, and these moieties are further elaborated to directly provide pyrroles or pyridines with extended conjugation. Reaction conditions are mild, and a broad range of structural types are available within a few steps.

Terrosamycins A (1) and B (2), two polycyclic polyether natural products, were purified from the fermentation broth of Streptomyces sp. RKND004 isolated from Prince Edward Island sediment. The one strain-many compounds (OSMAC) approach coupled with UPLC-HRMS-based metabolomics screening led to the identification of these compounds. The structure of 1 was determined from analysis of NMR, HRMS, and X-ray diffraction data. NMR experiments performed on 2 revealed the presence of two methoxy groups replacing two hydroxy groups in 1. Like other polyether ionophores, 1 and 2 exhibited excellent antibiotic activity against Gram-positive pathogens. Interestingly, the terrosamycins also exhibited activity against two breast cancer cell lines.

A series of thioarylmaleimides was synthesized to investigate how variation of the thioaryl group can be used to control absorption and emission properties in solution and in the solid-state. Fine-tuning of the photochemical properties was found to be possible using this strategy, and a rainbow of colours and emission wavelengths are accessible in a single step from commercially available compounds.

In this study we have studied the synthesis, characterization and catalytic activity of phosphinocopper(I) complexes [Cu(PPh3)(3)(NCCH3)][B(O2C6H4-4-R)(2)] (3a: R = H; 3b: R = Me; 3c: R = NO2) and [Cu(PPh3)(3)(NCCH3)][B(O2C6H3-3,5-di-Bu-t)(2)] (3d) containing weakly coordinating arylspiroborate ligands bearing various electronic and sterically defined characteristics. All new compounds have been characterized fully including single crystal X-ray diffraction studies for 3a and 3c and confirm that the arylspiroborate ligands do not coordinate to the copper atoms. Using these new metal complexes as precatalysts in the cyclisation of short chain alkynoic acids gave the corresponding exo-dig cyclic lactones exclusively. (C) 2019 Elsevier Ltd. All rights reserved.

The π-electron donor strength of a triphenylphosphonium ylidyl group (Ph3P[double bond, length as m-dash]CH-) was explored through its substitution onto a bispyridinylidene (BPY) scaffold. Electrochemical studies revealed that the new triphenylphosphonium ylidyl-substituted BPY is the most reducing di-substituted derivative reported to date (E1/2 = -1.55 V vs. SCE). By using a previously established correlation between the redox potential of the substituted BPYs and the corresponding substituent, a Hammett constant for the Ph3P[double bond, length as m-dash]CH- group was determined (σp+ = -2.33), establishing it as the most donating neutral substituent currently quantified. The BPY is readily oxidized by hexachloroethane to produce the corresponding dicationic bipyridinium salt as a mixture of isomers owing to hindered Cylidyl-Cpyridyl bond rotation. In preliminary tests of the BPY as a reductant, dichlorotricyclohexylphosphorane and chlorodiphenylphosphine were reduced to the corresponding phosphine and diphosphine, respectively.

Reaction of Ph2SbCl3 with 2,2'-bipyridine and Me3SiOSO2CF3 releases chlorobenzene, which is interpreted as a reductive (Sb-V/Sb-III) elimination from a complex of a stiboranium cation. Conversely, reactions of Ph2SbCl3 with 4-methylpyridine-N-oxide and AgOSO2CF3 give redox-resistant complexes with the generic formulae [Ph2SbCl3-xLx+1][OTf](x), including a compound containing a pnictogen(V) trication.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

We have synthesized bismuth complexes incorporating polydentate mono- and di-thiolate ligands and examined their utility as water-tolerant Lewis acid catalysts. The reaction of Bi(OAc)3 or Bi(NO3)3·5H2O and the corresponding mono- or di-thiol(ate) yielded the compounds [(SNNS)Bi(OAc)] (4), [(SNNSPr)Bi(OAc)] (5), [(NNS2)Bi(OAc)] (6), [(ONS2)Bi(OAc)] (7), [(ONS2)Bi(NO3)] (8), and [(NNS)2Bi][NO3] (9) [H2(SNNS) = N,N′-dimethyl-N,N′-bis(2-mercaptoethyl)ethylenediamine; H2(SNNSPr) = N,N′-diethyl-N,N′-bis(2-mercaptoethyl)propanediamine; H2(NNS2) = N,N-diethyl-N′,N′-bis(2-mercaptoethyl)ethanediamine; H2(ONS2) = 2-methoxyethyl-bis(2-mercaptoethyl)amine; H(NNS) = N,N-diethyl-N′-(2-mercaptoethyl)ethanediamine]. The solid-state structures of 4–8 show similar distorted pentagonal pyramidal geometries at the bismuth centre with a thiolate sulfur atom in the axial site, whereas 8 shows second structural arrangement with a distorted trigonal bipyramidal geometry at bismuth. The cation of 9 shows two NNS-bonded ligands and a distorted octahedral geometry at bismuth. Two-dimensional NMR studies of 4–8 show geminal 1H coupling in –SCH2CH2N– groups and suggests strong dative Bi–N intramolecular interactions. Bi(NO3)3·5H2O and BiCl3 show high activity toward the esterification of stearic acid, Bi(NO3)3·5H2O, and 4–7 and 9 show high activity toward the transesterification of methyl stearate in butanol, and 7 shows moderate activity as a catalyst for the transesterification of glyceryl trioctanoate in methanol.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Three new iminophosphines containing pinacol- derived boronate esters have been prepared and ligated to dichloridoplatinum(II) fragments. All compounds have been characterized fully, including an X-ray diffraction study carried out for the platinum complex 8, which is derived from 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl) aniline. These three new platinum complexes, along with the non-boron containing control, have been examined for their initial cytotoxic properties against two glioma cell lines using the MTT method.

Eight new aminoboron compounds derived from primary diamines and the pinacol-protected product of 3-fluoro-2-formylphenylboronic acid have been prepared and characterized fully. Reactions proceed to give the corresponding cyclic products arising via initial aldimine formation followed by a secondary hydroamination step. One compound contains a pendant amine group which was used to make a novel boron-containing Schiff base ligand along with the corresponding zinc(II) metal complex. All compounds were tested for their initial antimicrobial activities against a number of fungi and bacteria.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The addition of phosphinoboronate ester Ph2 PBpin (pin=1,2-O2 C2 Me4 ) (1) to a number of different N-heterocycles has been investigated. Reaction of 1 with pyridine resulted in highly selective formation of the corresponding 1,4-addition product, with addition of the electron-deficient Bpin group to the pyridine nitrogen atom and the phosphido group to the para carbon atom. Conversely, reactions of para-substituted pyridine derivatives occurred predominately to afford 1,2-addition products while quinoline reacted to afford the 1,2-adduct which ultimately isomerized to afford the corresponding 1,4-addition product. Preliminary computational studies have been undertaken to explore possible pathways for these transformations including transfer of the PPh2- anion from [B(PPh2 )2 pin]- to the 4-position of a borenium/boronium activated pyridine and concerted pathways for 1,2-addition via intramolecular nucleophilic attack of PPh2 at C2 of a Ph2 PBpin-coordinated pyridine via a four-centered transition state and intramolecular transfer of PPh2 to the 2-position of a boron-activated pyridine in a phosphido-bridged dimer involving a six-centered transition state.

We have synthesized indium complexes incorporating tetradentate dithiolate ligands. The 1:1 reaction of InX3 (X=OAc, NO3) and the corresponding dithiol or dithiolate yielded the compounds [(SOOS)In(py)(NO3)] (1), [(SNNS)In(OAc)] (2), [In(μ-SNNS)2(μ-OMe)In][NO3] (3), [(SNNSPr)In(OAc)] (4), [(NNS2)In(OAc)] (5) and [(NNS2)In(NO3)] (6) [H2(SOOS)=2,2′-(ethylenedioxy)diethanethiol; H2(SNNS)=N,N′-dimethyl-N,N′-bis(2-mercaptoethyl)ethylenediamine; H2(SNNSPr)=N,N′-diethyl-N,N′-bis(2-mercaptoethyl)propanediamine; H2(NNS2)=N,N-diethyl-N′,N′-bis(2-mercaptoethyl)ethanediamine]. The solid-state structures of 1, 2 and 4–6 are mononuclear and show a tetradentate SOOS/SNNS/NNS2 ligand and a distorted octahedral (1) or trigonal bipyramidal (2, 4–6) coordination geometry at indium. Compound 3 is dinuclear, with the indium centres bridged by a -OMe oxygen atom and a thiolate sulfur atom of chelating tetradentate ligands, respectively. InX3 (X=Cl, NO3) were found to be useful Lewis acid catalysts for the aldol reaction of benzaldehyde and 1-(trimethylsiloxy)cyclohexene under ambient conditions, while compounds 1–6 show moderate activity as catalysts for the esterification of stearic acid and transesterification of methyl stearate and glyceryl trioctanoate.