Polythiacrown macro- and gigantocycles with chiral diacetal cores

We present a unique class of polythiacrown macro- and gigantocyclic([9]) systems, consisting of ethylene 1,2-dithioglycol (ETG) to poly(ethylene thioglycol) (ETG(n)) bridges over one to six diacetal units of the cis-1,3,5,7-tetraoxadecalin (TOD) type. The latter is a dissymmetric, chiral moiety, incorporating a cavity with built-in high electron lone pair concentration, serving as the core of chiral macrocyclic host systems with good inclusion ability of ions and polar molecules. We describe two approaches: (i) the reactions of the 2,6-bis(bromomethyl)-cis-TOD podand (6) with ETG or higher ETG(n)s (12(n)), in Cs2CO3 promoted processes, leading to the innate but uncontrolled formation of polythiacrown-TOD macrocycles having ETG/TOD ratios of 1:1 (7), 2:2 (8) and further 3:3-6:6 (11(1/m)) macrocycles via open dithiol intermediates, and (ii) judicious preparation, using K2CO3, of oligomeric dibromide intermediates with ETG(n):TOD ratios 1:2, 2:3 or 3:4 (14(n/m)), which led (with further ETG(n)) in a controlled way to the 2:2 (8(n)), or 3:3, 4:4 and 6:6 (11(n/m)) macro- and gigantocyclic systems, Altogether, the outcome of these processes depends on the relative concentrations of the reactants. Synthesis was accompanied by detailed (NMR and MS) spectroscopy. X-ray crystallographic analysis of a number of macrocycles, complemented by (MM & MD) computation, made possible valuable structural, stereochemical and conformational analysis. While sophisticated in their stereochemical features, these systems are readily prepared in enantiopure form and hold great promise of chemical reactivity in metal ion inclusion and molecular and chiral recognition. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007).