Highly Sensitive Switchable Sensors for Hydroxide on Glass Surfaces Based on Isoquinolinium-Quinolinium-substituted Acetylenes

Bi-substituted acetylenes with a quinolinium and an isoquinolinium substituent are described, which reversibly form intensely colored adducts with O-nucleophiles and thus enable the detection of >0,5 ppm hydroxide on the surfaces of various glasses. Acids reconstitute the colorless bi-substituted acetylenes. The quinolinium and isoquinolinium rings are bound via their 2-, 3-, 4- and 1-, 3-, 4-positions to the triple bond, respectively. The choice of substitution sites of the hetarenium rings enables the design of mixed conjugated/cross-conjugated π-electron systems. Depending on the combination of binding sites, the frontier orbital profile, the triple bond polarization, the fluorescence behaviour, and the sensitivity to hydroxide differs.

Bromoarylation of Methyl 2-Chloroacrylate under Meerwein Conditions for the Synthesis of Substituted 3-Hydroxythiophenes

Methyl 3-aryl-2-bromo-2-chloropropanoates can be prepared by Meerwein reaction from methyl 2-chloroacrylate and various arenediazonium salts under copper(II) bromide catalysis. The resulting readily available compounds were used as starting materials in reactions with substituted methanethiols for the construction of substituted 3-hydroxythiophenes which have not yet been accessible by other routes. Structural variety of the obtained 2-substituted 5-aryl-3-hydroxythiophenes has been achieved due to a wide range of available starting materials, including both anilines and thiols.

Synthesis and characterization of propeller-shaped mono- to hexacationic quinolinium-substituted benzenes

Diels-Alder reaction of 2-, 3- and 4-(phenylethynyl)quinolines and tetraphenylcyclopentadienone gave three regioisomeric 2,3,4,5,6-pentaphenyl-1-(quinolin-2-yl, -3-yl, and -4-yl)benzenes. Restricted rotation of the 3-yl and 4-yl substituted derivatives is observed between the central core and the substituents, resulting in propeller-shaped molecules. Likewise, 1,2-diquinolinyl-3,4,5,6-tetraphenylbenzenes with 3-yl,3-yl and 3-yl,4-yl connectivity were prepared. As evidenced by NMR spectroscopy, they form two diasteromers due to their restricted rotation. A cobalt-catalyzed [2 + 2 + 2]-cyclotrimerization of 2-(phenylethynyl)quinoline resulted in the formation of triphenyl-2,4,6- and -3,5,6-tri(quinolin-2-yl)benzenes. The same reaction was applied to 3,3'-ethyne-1,2-diyldiquinoline which formed hexa(quinolin-3-yl)benzene. N-Methylation gave the title compounds. Among those, the hexacationic hexa(N-methylquinolinio-3-yl)benzene is described. Stereochemical aspects are predominantly discussed by means of results of NMR experiments. DFT-calculations on the most stable conformations and the frontier orbital profiles of the hexacation as well as of its neutral precursor have been carried out.