The thyme polyethers : An approach to the synthesis of a molecular knotted ring

Recent progress on a realization of the Möbius strip approach to the synthesis of a molecular trefoil knot is discussed. Specifically, the synthesis and cyclization of a 4-rung ladder-shaped diol-ditosylate composed of crown ether rings fused by the tetrahydroxymethylethylene (THYME) unit are presented. In addition, some novel results in low dimensional topology deriving from consideration of the geometry of the novel molecular graphs defined by the subject compounds are discussed.     

Toward electron encapsulation: polynitrile approach

This study seeks an answer to the following question: Is it possible to design a supramolecular cage that would "solvate" the excess electron in the same fashion in which several solvent molecules do that cooperatively in polar liquids? Two general strategies are outlined for this "electron encapsulation", viz. electron localization using polar groups arranged on the (i) inside of the cage or (ii) outside of the cage. The second approach is more convenient from the synthetic standpoint, but it is limited to polynitriles. We demonstrate, experimentally and theoretically, that this second approach faces a problem: the electron attaches to the nitrile groups, forming molecular anions with bent C-C-N fragments. Because the energy cost of this bending is high, for dinitrile anions in n-hexane, the binding energies for the electron are low and, for mononitriles, these binding energies are lower still, and the entropy of electron attachment is anomalously small. Density functional theory modeling of electron trapping by mononitriles in n-hexane suggests that the solute molecules substitute for the solvent molecules at the electron cavity, "solvating" the electron by their methyl groups. We argue that such species would be more correctly viewed as multimer radical anions in which the electron density is shared (mainly) between C 2p orbitals in the solute/solvent molecules, rather than cavity electrons. The way in which the excess electron density is shared by such molecules is similar to the way in which this sharing occurs in large di- and polynitrile anions, such as 1,2,4,5,7,8,10,11-octacyanocyclododecane(-). Only in this sense is the electron encapsulation possible. The work thus reveals limitations of the concept of "solvated electron" for organic liquids: it is impossible to draw a clear line between such species and a certain class of radical anions.     

Towards an enantiospecific total synthesis of garsubellin A and related phloroglucin natural products: the α-pinene approach

The first enantiospecific approach to garsubellin A and related phloroglucin natural product nemorosone, of contemporary interest from (−)-α-pinene, has been delineated. Through a series of stereospecific operations, the requisite stereochemistry of the prenyl groups has been secured. Kende cyclization has been employed as the key step to construct the functionalized bicyclo[3.3.1]nonane core.     

Towards the total synthesis of clavosolide A

The synthesis of the monomeric unit of clavosolide A from 1,2:5,6-di-O-isopropylidene-α-d-glucose is presented.     

A new approach to the synthesis of telluranthene

A series of new methods of synthesizing telluranthrene are proposed, based on the use of poly(o-phenylene)ditelluride and its precursors. The best yields of telluranthene are obtained by the reactions of the disodium salt of o-ditellurolobenzene with o-diiodobenzene (50–62%) and of poly(o-phenylene)ditelluride with butyllithium.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1424–1427, October, 1991.     

A metathesis-based approach to the synthesis of furans

The enol ether-olefin ring-closing metathesis reaction has been employed to generate 2,3-dihydrofurans that are equipped with a leaving group. These substrates are at the correct oxidation state to undergo an acid-catalyzed aromatization, and this strategy has been utilized to provide a mild and rapid route (four steps) to a range of novel 2,5-disubstituted furans. [reaction: see text]     

A Pauson-Khand approach to the synthesis of ingenol

[reaction: see text] Pauson-Khand cyclization of dioxanone photoadduct 21 leads to the formation of a single product in good yield. However, retro-aldol fragmentation of the pentacyclic cyclopentenone 22 leads to the formation of 23, with cis C-8/C-10 intrabridgehead stereochemistry, unlike the target compound ingenol 1, which possesses C-8/C-10 trans intrabridgehead stereochemistry.     

A novel approach to molecular similarity

Summary We review briefly the general problem of assessing the similarity between one molecule and another. We propose a novel approach to the quantitative estimation of the similarity of two electron distributions. The procedure is based on momentum space concepts, and avoids many of the difficulties associated with the usual position space definitions. Results are presented for the model systems CH₃CH₂CH₃, CH₃OCH₃, CH₃SCH₃, H₂O and H₂S.     

A new approach to the molecular rotational hamiltonian

The present paper is devoted to a new approach of the rotational hamiltonian of a non degenerate vibronic state of the semi-rigid molecules. It is based upon two points. Firstly the hermitian operators on a finiten dimensional vector space belong to an ² dimensional euclidian vector space. Secondly, the vector space of the rotational states is a direct sum of irreducible representations of the rotation group. Accordingly in each one of those representations the rotational hamiltonian can be represented by its set of real components on a orthonormal basis of hermitian operators. The components of the reduced hamiltonian of Watson limited to its quartic terms are determined.     

Self-assembly of supramolecular chiral insulated molecular wire

Supramolecular chiral insulated molecular wire was constructed by self-assembly of a neutral one-dimensional schizophyllan host and a water-soluble polythiophene guest. The work presented here will not only open a door to a new application of polysaccharides but also provide an important clue to prepare stable supramolecular insulated molecular wires with one-handed helical structure.