David W. Purkiss

Highly Stereoselective α-Hydroxyalkylation/Chlorination of α,β-Acetylenic Ketones—An Efficient Approach to β-Halogeno Baylis–Hillman Adducts

Abstract A highly stereoselective method for the synthesis of (E)-β-halogeno Baylis–Hillman adducts has been developed. The new method involves a tandem α-hydroxyalkylation/β-chlorination of α,β-acetylenic ketones by using TiCl4 as the chlorine source for α,β-conjugate addition, and concurrently as the Lewis acid promoter for the carbonyl addition. The new system tolerates a broad scope of reactants in which aliphatic and aromatic α-acetylenic ketones can be subjected to the conjugate addition. Both aliphatic and aromatic aldehydes can also be employed as electrophilic acceptors. Good yields (61–88%) and high E/Z stereoselectivity have been obtained for the nine examples which were examined, only in one case was E/Z selectivity of 17/1 observed and the two individual isomers are separable via flash column chromatography.

Proton di-ionizable p-tert-butylcalix[4]arene-crown-6 compounds in cone, partial-cone and 1,3-alternate conformations: synthesis and alkaline earth metal cation extraction

Novel proton di-ionizable p-tert-butylcalix[4]arene-crown-6 compounds in cone, partial-cone and 1,3-alternate conformations are synthesized to compare the efficiency and selectivity with which they extract alkaline earth metal ions. In these ligands, a crown-6 polyether unit links alternate aromatic rings of the calix[4]arene framework. To the remaining lower-rim positions are attached oxyacetic acid or N-(X)sulfonyl oxyacetamide groups. Changing the conformation varies the spatial relationship between a polyether-complexed divalent metal ion and the ionized side arms of the ligands. This is found to markedly affect the efficiency and selectivity in competitive solvent extraction of alkaline earth metal ions from aqueous solutions into chloroform by the di-ionizable calix[4]arene-crown-6 ligands.

Stereoselective aldol coupling of α,β-acetylenic ketones promoted by MgI2

A highly stereoselective synthesis of (Z)-β-iodovinyl ketone has been achieved with the tandem formation of CC and CI bonds in a three-component reaction. This new catalysis utilizes MgI2 as a Lewis acid as well as an iodine source for a Michael-type addition. α,β-Acetylenic ketone is initially converted to an active β-iodo allenolate intermediate and then can be attacked by a variety of aldehydes to afford Z-selective Baylis–Hillman adducts in excellent yields.

Di-ionizable p-tert-butylcalix[4]arene-1,2-crown-3 ligands in cone and 1,2-alternate conformations: synthesis and metal ion extraction.

Novel di-ionizable p-tert-butylcalix[4]arene-1,2-crown-3 ligands in cone and 1,2-alternate conformations were prepared as potential metal ion extractants. Selective bridging of proximal hydroxyl groups of the calix[4]arene platform by a crown-3 polyether unit was achieved under Mitsunobu reaction conditions. In addition to the carboxylic acid group, the acidity tunable N-(X)sulfonyl oxyacetamide functions [OCH(2)C(O)NHSO(2)X] with X group variation from methyl to phenyl to p-nitrophenyl to trifluomethyl were used as the proton-ionizable groups. Conformations and regioselectivities of the new ligands were established by (1)H and (13)C NMR spectroscopy. Competitive solvent extractions of alkali metal cations and of alkaline earth metal cations from aqueous solutions into chloroform were performed, as were single species extractions of lead(ii) and mercury(ii).

Effect of para-substituents on alkaline earth metal ion extraction by proton di-ionizable calix[4]arene-crown-6 ligands in cone, partial-cone and 1,3-alternate conformations

Two carboxylic acid or N-(X)sulfonyl carboxamide groups were incorporated into calix[4]arene-crown-6 compounds to afford di-ionizable ligands for use in divalent metal ion separations. Acidities of the N-(X)sulfonyl carboxamide groups were tuned by variation of the electron-withdrawing properties of X. Cone, partial-cone and 1,3-alternate conformations were obtained by different synthetic strategies and their structures verified by NMR spectroscopy. Competitive solvent extractions of alkaline earth metal cations from aqueous solutions into chloroform were performed and the results compared with those reported previously for di-ionizable p-tert-butylcalix[4]arene-crown-6 analogues to probe the influence of the para-substituent on the calix[4]arene scaffold on extraction selectivity and efficiency.

New ditopic receptors for alkylammonium ion complexation

New receptor molecules have been synthesized in which α,α′-bis-(4-hydroxyphenyl)-1,4-diisopropylbenzene is linked to 1,10-diaza-18-crown-6, 1,10-diaza-21-crown-7 or 1,13-diaza-24-crown-8 units by ethylene or 1,4-butylene bridges. Binding abilities of the new receptors and the model compoundN,N-didecyl-1,10-diaza-18-crown-6 toward alkali metal cations and alkylammonium ions were assessed by picrate extraction. Spectral evidence for inclusion of alkylammonium ions within the receptor cavity was obtained by1H NMR spectroscopy. From a1H NMR titration experiment conducted in CDCL3−CD3OD (9∶1), a relatively strong inclusion complex (Ka ∼ 900M−1) of the receptor having a 1,10-diaza-18-crown-6 subunit and ethylene spacers with propylammonium picrate was observed.