Concave reagents, 8. Concave pyridines and 1,10‐phenanthrolines with sulfonamide bridgeheads. Increased basicity by 4‐diethylamino substitution of the pyridine unit

Abstract

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.

Synthesis of poly(pyridylthioether) dendrimers incorporating a Fe2(CO)6 cluster core

“…16 Subsequent reduction of the ester functionalities to alcohols, using NaBH 4 in methanol, 17 afforded diol 3 in 96% yield. Halopyridine 3 was then treated with boronic acid 4, prepared 18 in high yield and purity from 4-bromobenzenethiol, employing the Suzuki cross-coupling conditions (toluene/H 2 O, Na 2 CO 3 , Pd(PPh 3 ) 4 ) to give the arylsubstituted pyridine derivative 5 in 61% yield after chromatographic purification.…”

Synthesis of new enantiopure dimethyl- and diisobutyl -substituted pyridino-18-crown-6 ethers containing a halogen atom or a methoxy group at position 4 of the pyridine ring for enantiomeric recognition studies

“…18 In the latter literature, this type of diols were not isolated. A modified procedure of Lüning et al 19 was used to synthesize chloro-diol 18. Instead of the long time (2 days) continuous extracting, we isolated 18 by recrystallization from water.…”

Concave Pyridines for Selective Acylations of Polyols

“…As described in the literature or analogously (see Scheme 1 and Experimental), the catalysts 1 and 2 [5] [6] and diphenylketene [7] have been synthesized. To synthesize 1c and 2c, first an ethoxy group was introduced in 4-position Scheme 1 Eur.…”

“…In the NMR spectra, amide conformers were only found below room temperature. [5] 63 25 12 1b [5] 54 28 18 1c 34 46 20 2a [5] 75 ഠ23 <5 2b [5] 68 27 5 2c 68 27 5 2d [6] 71 23 6 2e [10] 66 28 6 2f [10] 66 28 6 dendrimer A [10] 61 33 6 dendrimer B [10] 62 33 5…”