Synthetic studies toward longeracemine: a SmI2-mediated spirocyclization and rearrangement cascade to construct the 2-azabicyclo[2.2.1]heptane framework

Longeracemine, a member of the Daphniphyllum family of alkaloids contains a novel carbon framework featuring a highly functionalized 2-azabicyclo[2.2.1]heptane core as part of an overall 5/6/5/5/6/5 skeleton. A synthetic intermediate containing the core of longeracemine has been efficiently prepared by employing a stereoselective SmI₂-mediated cascade reaction to advance a 7-azabicyclo[2.2.1]heptadiene to a 2-azabicyclo[2.2.1]heptene that is functionally poised for conversion to the natural product.

A synthetic intermediate containing the core of longeracemine, that is functionally poised for conversion to the natural product, has been efficiently prepared by employing a stereoselective SmI₂-mediated cascade reaction.     

The use of charcoal from agriculture waste in the speciation of iodine from well and river waters

The concentrations of iodine in fresh waters are known to be within the range of 0.5 to 35 ng·ml⁻¹, much lower than in oceanic waters. The iodine concentrations, particularly that of¹²⁹I which is significant from the radiation safety aspect, in public drinking waters have to be specified in order to verify the required level before distribution for domestic use. A modified version of an established method was used in the adsorption of iodine, iodate, total inorganic iodine and charcoal-adsorbable iodine using activated carbon prepared from oil palm kernel wastes. A thorough investigation of the physical properties of the activated carbon was carried out to determine its viability as an adsorbent for volatile species such as iodine. The iodine species were preconcentrated from water samples collected from wells in villages and from water intake points along rivers. The quantitative analysis of the species adsorbed was done by irradiating the activated charcoal loaded with the respective species in a neutron flux of 5.1·10¹² n·cm⁻²·s⁻¹ from a TRIGA MkII, nuclear reactor. Recovery experiments using spiked samples was done to provide quality assurance controls.     

Thieno[3,4-b]pyrazines: synthesis,structure, and reactivity

A general synthetic route has been developed for the efficient preparation of 2,3-disubstituted thieno[3,4-b]pyrazines. These methods eliminate problems in the preparation of the precursor 3,4-diaminothiophene and utilize alpha-diones prepared through the reaction of the appropriate organocuprates with oxalyl chloride. This combination allows the convenient preparation of thieno[3,4-b]pyrazine and its 2,3-disubstituted analogues (where substituent = methyl, hexyl, octyl, decyl, dodecyl, and phenyl) in high yield. Characterization of the structure and reactivity of this class of compounds is also described, including the results of structural, electrochemical, and pK(a) studies.     

Propane phosphonic acid anhydride: a new promoter for the one-pot Biginelli synthesis of 3,4-dihydropyrimidin-2(1H)-ones

Propane phosphonic acid anhydride has been found to promote the Biginelli synthesis of 3,4-dihydropyrimidin-2(1H)-ones. The use of this agent is characterized by moderate costs, low toxicity and simple workup conditions.     

2–3 brother trees

2–3 brother trees form a dense class of search trees havingO(logN) insertion and deletion algorithms. In this paper we provide anO(logN) insertion algorithm and show that these trees have much better density and storage utilization than 2–3 trees. Thus we demonstrate that the brother property which has so far been used only for binary trees can be usefully applied to 2–3 trees.Work supported partially by a Natural Sciences and Engineering Research Council of Canada Grant No. A-7700 and partially by the German Academic Exchange Service under Nato Research Grant No. 430/402/584/8.     

Eigenvalues for Perturbed Periodic Jacobi Matrices by the Wigner-von Neumann Approach

The Wigner-von Neumann method, which has previously been used for perturbing continuous Schrödinger operators, is here applied to their discrete counterparts. In particular, we consider perturbations of arbitrary \({T}\)-periodic Jacobi matrices. The asymptotic behaviour of the subordinate solutions is investigated, as too are their initial components, together giving a general technique for embedding eigenvalues, \({\lambda}\), into the operator’s absolutely continuous spectrum. Introducing a new rational function, \({C(\lambda; T)}\), related to the periodic Jacobi matrices, we describe the elements of the a.c. spectrum for which this construction does not work (zeros of \({C(\lambda; T)}\)); in particular showing that there are only finitely many of them.     

Evolution of a synthetic strategy: total synthesis of (+/-)-welwitindolinone A isonitrile

An efficient and highly stereoselective total synthesis of the natural product (+/-)-welwitindolinone A isonitrile (1) is described. The bicyclo[4.2.0]octane core of 1 was established by a regio- and diastereoselective [2+2] ketene cycloaddition. The C12 quaternary center and vicinal stereogenic chlorine were installed in a single operation with excellent stereocontrol via a chloronium ion mediated semipinacol rearrangement. Described strategies for construction of the spiro-oxinole include a SmI2-LiCl mediated reductive cyclization and a novel anionic cyclization that simultaneously constructs the spiro-oxindole and vinyl isonitrile moieties.     

Stereoselective Synthesis of 1,1’,2,2’-Tetrasubstituted Ferrocenes by Double Lithiation of a 1,1’-Disubstituted Ferrocenyl Pyrroloimidazolone

A 1,1’-disubstituted ferrocenyl pyrroloimidazolone with syn stereochemistry undergoes double lithiation–electrophile quench in a one-pot procedure to give C₂-symmetric 1,1’,2,2’-tetrasubstituted products in >95 : 5 diastereomeric ratio (dr). These results represent an extension of double lithiation to access tetrasubstituted planar chiral ferrocenes for the first time to a nitrogen-linked (pyrroloimidazolone) chiral directing group. The stereochemistry of the products was determined by X-ray crystallography of distannane and dibromide adducts in combination with deuteration, elimination, and transmetalation experiments. Results support that products arise from selective deprotonation of the pro-S_p position of each cyclopentadienyl (Cp) ring.