Eight new bimacrocyclic concave pyridines 9 and six monomacrocyclic and open-chain analogues 10 -12 were synthesized in overall yields up to 40% (up to 75% for nonmacrocyclic pyridines) starting from 2,6-pyridinedicarbaldehydes 1, diamines 2 and diacyl dichlorides 7. Their basicities cover a range of more than three orders of magnitude. They are determined not only by the substitution pattern of the pyridine ring, but also by the overall structure of the whole molecule and by its ability to stabilize the positive charge of a proton intramolecularly. The conformations of the bimacrocyclic bislactams 9 in solution and in the solid state were investigated spectroscopically, the structure of 9 b could be determined by X-ray analysis.Concave pyridines 9 have been developed') to act as specific concave reagents in proton-transfer reactions (deprotonations, protonations). In these reactions, two properties of the concave base will determine the course of the reaction: the basicity of the base and the geometry of its concave shielding. In order to be able to pick an appropriate concave base for a given problem, the factors which determine the basicity of the base and its three dimensional shape must be known. Therefore, a variety of concave pyridines 9 and analogue 10 -12 was synthesized, their basicities were measured, and their conformational behaviour was investigated. SynthesesIn Scheme 1, the synthesis of concave pyridines 9 and their analogues 10-12 is laid out. Concave pyridines 9 could be obtained by two cyclization steps using 2,6-pyridinedicarbaldehydes 1, diamines 2 and diacyl dichlorides 7 as starting materials. The use of dialdehydes 1, monoamines 3, and diacyl dichlorides 7 led to the monomacrocyclic analogues 11. Diacetylated monomacrocyclic and open-chain products 10 and 12 were obtained when acetic anhydride (8) was used instead of a diacyl dichloride 7.2,6-Pyridinedicarbaldehyde (1 a) was accessible starting either from 2,6-dimethylpyridine (13) or from 2,6-pyridinedicarboxylic acid via the dialcohol 14a.Analogous to the oxidation of 2,9-dimethyl-l,lO-phenanthr~line'.~), direct SeOz oxidation of 2,6-dimethylpyridine (13) was possible but yielded only 26% of the dialdehyde 1 a4). Better yields of l a could be achieved by oxidation of 2,6-pyridinedimethanol (14a), which was accessible5) from 2,6-pyridinedicarboxylic acid by NaBH4 reduction of its dimethyl ester (total yield up to 80%). MnOz oxidation6) of 14a gave up to 60% of the dialdehyde l a but the procedure had two drawbacks: Mn02 had to be freshly precipitated and well powdered (reproducibility problems) and the amount of M n 0 2 needed was enormous (i.e. 130 g of MnOz for 12 g of alcohol 14a). A smaller amount of reagents was required for the oxidation of 14a with DMSO/oxalyl chloride') (ca. SO%), but dimethyl sulfide is produced in this reaction (an olfactory problem), and the scale is limited by the reaction temperature (-78 "C). The best oxidation procedure is a Se02 oxidation of 14a8), leading to the aldehyde l a in up to 90% yield. 4-Methox...

No abstract

SUMMARY:The shell material core coverages of two-phase core-shell particles are determined quantitatively by NMR spin-diffusion experiments. A simple relation is derived between the specific surface (ratio of core surface and core volume) and the core coverage of acrylic core-shell particles in the solid state. Through calibration with a reference sample of known core coverage, the core coverage of the other samples can then be evaluated. The values of core coverages determined by spin-diffusion become more accurate as the core coverage becomes smaller. In a series of poly(methyl methacrylate) (PMMA) and poly(butyl acrylate) coreshell latices, the core coverage was found to vary between 43 and 80%. Additionally, information about the global particle morphologies is derived from a quantitative comparison of the specific surface and the particle diameter measured by dynamic light scattering.

Bimacrocyclic concave pyridinebissulfonamides 2 and concave 1,lO-phenanthrolinebissulfonamides 4 have been synthesized by bridging macrocyclic pyridinediamines 12 or 1,lOphenanthrolinediamines 16 with alkylenebis(sulfony1 chloride)s 14. In contrast to concave pyridine-and $10-phenanthrolinebislactams 1 and 3, the new compounds 2 and 4 exhibit simpler 'H-NMR spectra and sharper melting points due to the absence of amide conformers; in comparison to 1, the basicities of 2 are decreased by a factor of ca. 100. By introduction of donor substituents into the 4-position of the pyridine ring the basicity loss can be easily compensated. The 4-diethylamino substituent increases the basicity of the concave pyridines 1 and 2 as expected (ca. + 4 pK units). Since no deviations from the expected basicity and reactivity for the amino-substituted concave pyridines 1 and 2 have been found, also in these sterically hindered pyridines, the pyridine nitrogen atom is the centre of basicity and reactivity. -The synthesis of new building blocks is described, i.e. 4-diethylamino-2,6-pyridinedicarbaldehyde (Sc), the polyether-based bis(sulfony1 chloride) 14b, the monomacrocyclic diamines 12e -h with a pentaethyleneglycol chain or a 4-diethylamino substituent.Concave reagents have been designed to improve the selectivity of standard chemicals of organic chemistry by combination of concave structures with standard reagents. Up to now, concave benzoic acids, concave 1,lO-phenanthrolines and concave pyridines have been Especially the latter compounds 1 showed remarkable selectivities when they were used as proton-transfer reagents in reprotonation reactions of nitronate anions. In these investigations, substrate selectivity3) and the "soft Nef rea~tion"~) have been found. In a second model reaction, the concave pyridines 1 and 2 were used as catalysts in the alcoholysis of ketenes5).But predictions regarding the mechanism of these reactions are difficult to make because (almost) all concave pyridines 1 and concave 1,lO-phenanthrolines 3 which are based on carboxamide bridgeheads exist as mixtures of conThis is caused by the fact that carboxamides may exist as E and Z conformers, leading to Z / Z , ZJE and E/E mixtures for the concave pyridines 1 and concave 1,lOphenanthrolines 3. It is therefore desirable to replace the carboxamide bridgehead systems in these concave bases by units which will not form conformers. In comparison to carboxamides, sulfonamides have a lower barrier to rotation between the nitrogen atom and the sulfonyl group at room temperature6). Therefore, bimacrocyclic concave bissulfonamides 2 and 4 should exist as one single conformer. The strategy for the synthesis of such molecules should be similar to the synthesis of the concave bislactams 1 and 3 (see Scheme 2). Only in the second macrocyclization step, bis-(sulfonyl chlorides) 14 must be used instead of dicarboxylic acid dichlorides 13.

No abstract