Effect of counterion structure on micellar growth of alkylpyridinium surfactants in aqueous solution Bijma, K; Rank, E.; Engberts, J.B.F.N. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. This paper describes the influence of counterions on the unidirectional growth of micelles formed by alkylpyridinium surfactants in aqueous solution. It is shown that the growth of spherical micelles to form wormlike micelles is strongly dependent on counterion structure. More hydrophobic counterions induce the formation of wormlike micelles at lower surfactant concentrations. Next to hydrophobicity and the type of substituent, the substitution pattern of the aromatic ring plays the most important role in micellar growth. The formation of a network of entangled, elongated wormlike micelles by alkylpyridinium surfactants with o-hydroxybenzoate and p-chlorobenzoate counterions is discussed in terms of surfactant structure. It is concluded that, next to counterion structure, the microenvironment of the counterion (substituent) in the Stern region and the structure of the surfactant monomer (i.e., the surfactant cation) play the most important role in the formation of these elongated wormlike micelles. Headgroup effects are proposed to be the main driving force for this phenomenon.

Methyl trans-3-pentenoate (7) was converted into the cis-substituted g-lactone 8 in a single step with 78 % ee. The derived enolate dilithio-8 was alkylated trans-selectively with primary iodoalkanes. with 1-iodobutane dilithio-8 afforded, after esterification with isovaleroyl chloride, the epi-blastmycinone 9. Dilithio-8 gave (À)-grandinolide (11) with 1-iodo-19-phenylnonadecane (20). A third trans-selective alkylation of dilithio-8 was undertaken with 16-iodo-1,5-hexadecadiene-7,9-diyne (21). This gave the g-lactone 12, which had the published relative configuration of (À)-sapranthin but different spectroscopic data. When the OH group of lactone 8 was inverted (to hydroxylactone 40) and the derived enolate dilithio-40 alkylated with iodide 21, lactone 41 resulted. Its 1 H and 13 C NMR spectra and the sign and value of optical rotation coincide with the data of natural sapranthin. These findings establish that (À)-sapranthin possesses the relative and absolute configuration of stereoformula 41.

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A McMurry Route to the Dienediyne Portion of Models of the Neocarzinostatin Chromophore. -Key step in the synthesis of the title compounds (IV) is the intramolecular McMurry coupling of dicarbonyls (III) which are prepared via a Sonogashira-Thoda-Hagihara coupling of intermediate (I) with iodo cyclohexenone. (I) is obtained using established methods in alkyne chemistry. Model (IVa) undergoes cycloaromatization by the Saito-Myers mode on reaction with methyl thioglycolate. -(RANK, E.; BRUECKNER, R.; Eur.