Sarah Abramson

New supramolecular host systems. 41. novel diacetal podands, diazacrowns and cryptands

Abstract New and important key podands bearing the cis -1,3,5,7-tetraoxadecalin (TOD) core are reported, viz., 2,6-di(hydroxymethyl)- ( 2 ) and 2,6-di(aminomethyl)- cis -1,3,5,7-TOD ( 6 ), which lead to the first diazacrown-TOD compounds ( 9a ) and ( 9b ) and a corresponding cryptand ( 11 ) in the series. 9a&b exhibit very good alkali and earth-alkali ion inclusion ability with selectivity for K + and Ba +2 . Molecular dynamics (Insight/Discover/AMBER) on the crowns and cryptand were performed, including reparametrized MM3-GE calculations. A convincing case for the TOD based hosts was thus established.

New supramolecular host systems. 1. A structural and conformational study of the 1,3,5,7-tetraoxadecalin core system

Abstract This is the first in a series of studies of new host systems based on the 1,3,5,7-tetraoxadecalin (TOD) core moiety. The parent molecule ( 2 ) an

Photoresponsive lower-rim azobenzene substituted and bridged calix[4]arenes

Abstract The doubly azobenzene-chain lower-rim substituted calix[4]arenes 6 – 9 were prepared, followed by the doubly bridged biscalix[4]arenes 10 and 11 . All are photoresponsive and detailed studies of the E⇌Z photoisomerization and the Z → E thermal isomerization in 6 and 10 were carried out using UV and 1 H NMR spectroscopic techniques. The three ( EE , EZ and ZZ ) isomers of 6 and 10 were isolated or enriched and fully characterized by 1 H NMR. Kinetic analyses of these transformations of 6 were carried out and revealed a concentration dependent behavior and an interesting sequential course of its photoisomerization.

trans- and cis-1,3,5,7-Tetraazadecalin (TAD). A New and Strong Binding Mode in cis-TAD Chelates of Heavy Metal Ions

Abstract trans- and cis-1,3,5,7-tetraazadecalin (TAD) (2 & 3) were isolated and structurally characterized (VT-NMR). One of the cis-TAD derivatives intended to act as “cores” of new host systems, 2,6-di(hydroxymethyl)-cis-TAD (5), gave heavy metal ion (CdII, PbII, etc.) complexes with remarkably high binding constants, as measured by polarography. X-ray analyses of the CdII (7a) and PbII (7b) complexes revealed a new, unique binding mode.

The synthesis of barbaralyl systems via bicyclic[3.2.2] irontricarbonyl cations

Abstract Reaction of bicyclo[3.2.2] tertiary alcohols 7b,c and 23b with Fe 2 (CO) 9 , resulted in the corresponding dienyl Fe(CO) 3 complexes, which upon HBF 4 /Ac 2 O treatment yielded the bicyclo [3.2.2] dienyl irontricarbonyl cations. Nucleophilic addition of CN - to those cations, resulted in the formation of δ,μ-bonded complexes, which were degraded with Me 3 NO to give substituted tricydic hydrocarbons (barbaralyl systems) in unusual positions. For purpose of comparison, the trifluoroacetolysis of 2-methyl-endo-6,7-benzobicyclo[3.2.2] nonatriene ( 22 ) has been studied.

Oligomerization of 1,2‐Ethanedithiol: An Expedient Approach to Oligothiaethylenethioglycols

Reactions of ethylenedithioglycol (ETG) with Na(2)CO(3), K(2)CO(3), and Cs(2)CO(3) provided the oligothiaethylenethioglycols (nETG): di- (DETG), tri- (TrETG), tetra- (TETG), and pentathiaethylenethioglycol (PETG), along with higher polymers. The most efficient carbonate was K(2)CO(3) and reactions using DETG and TrETG as starting materials--or their mixtures--were also found to afford similar species. This largely unknown oligomerization process was thoroughly explored and potential pathways were put forward. A convenient conversion of ETG to laboratory quantities of the otherwise scarce and/or expensive DETG, TrETG, TETG, and PETG oligomers, in organic or aqueous media was achieved. Notably, this straightforward reaction takes place without the addition of expensive or toxic metal catalysts and with pure water as the solvent, thereby highlighting its potential as a green chemical reaction. Moreover, the process opens up new approaches to dynamic combinatorial libraries (DCLs) of oligomers and macrocycles with manifolded nETG [(SCH(2)CH(2))(n)S] bridges.

Glycosidation of 3,4,6-Tri-O-Benzyl-2-Ethenyl-D-Glucal – A Route to 2-C-(β-Methyl)Methylene Glycosides

ABSTRACT Monosaccharidic and disaccharidic 2-C-(β-methyl)methylene glycosides were synthesized by an electrophilic conjugate addition reaction of ROH-type compounds in the presence of Ph3P+H Br− to 2-ethenyl-3,4,6-tri-O-benzyl-D-glucal 1, functioning as a model glycosyl donor. This 2-vinyl glucal derivative represents a series of 2-vinyl and 2-butadienyl glycals, prepared by Wittig-type methylenation of pyranosidic conjugated enals, derived from glucal, galactal and lactal. The exo-(β-methyl)methylene group paves the way for further chemical transformations.

Photochemical behaviour of biased homo-conjugated ketones: details of an oxa-di-π-methane rearrangement

The acetone sensitized irradiation of the three spiro [5.5]undeca-1,3-dien-7-ones (1),(2), and (3) leads to two types of annelated bicyclo[3.1.0.]hexen-2-yl ketone products, the structures of which were assigned by n.m.r. spectroscopy and confirmed by X-ray crystallography; the results are interpreted in terms of a substitution-influenced 1,2-acyl shift, involving one or both double bonds, with an oxa-di-π-methane type mechanism.

Synthesis and photochemistry of 2,3,8,9-tetrahydroindenone-1

Abstract The novel β,γ,δ,e-unsaturated ketone ( 2 ) was prepared and all its photoproducts were identified, following wavelength dependent, irradiation-induced transformations.

On cyclopentadienone-ketals and their dimers. A novel rearrangement of α,β-unsaturated ketone dialkyl ketals

Abstract The dimers 2a & b) of dimethyl- and diethylcyclopentadienone ketals( 1a & b) undergo a novel 1,3-alkoxy-rearrangement to 4 (a & b). Mild hydrolysis of 2 or 3 gives the monoketones ( 3 a or b). On strong acid catalysed hydrolysis 2 , 3 or 4 afford the cyclopentadienone-dimer( 6 .