Molecular Tweezers: Synthesis and Formation of Host–Guest Complexes

Abstract

A chiral molecular tweezer obtained from (+)‐usnic acid placed in solution in the presence of various aromatic compounds afforded complexes with low association constants. Thus, the X‐ray structure of assembly 3i is presented, where the guest is sandwiched between the two pincers of the tweezer. The association constants for various guests were determined through different methods. Finally, other tweezers with electron‐rich aromatic aldehydes and ketones were prepared from (1R,2R)‐1,2‐diaminocyclohexane. The most interesting complexes were also confirmed through structural analysis, and the best results were obtained with 10‐hydroxyphenanthrene‐9‐carbaldehyde (5i) as the aromatic moiety.

Intramolecular Hydrogen Bonds in Normal and Sterically Compressed o-Hydroxy Aromatic Aldehydes. Isotope Effects on Chemical Shifts and Hydrogen Bond Strength

“…The light amber solid was purified by flash column chromatography on silica gel, using dichloromethane/ n-hexane (2:1) to afford the pure product as off white solid (1.2 g, 91%). The NMR data are consistent with that reported in the literature [31] 10-Methoxy-9-phenanthrenealdehyde: This compound was synthesized by modification of literature methods [31]. The resulting light brown solid residue was purified by flash column chromatography on silica gel, using an eluent gradient of n-hexane/dichloromethane/(2:1), then (1:1) and finally (1:4) to give a white solid (0.83 g, 67% 10-Hydroxy-9-phenanthrenealdehyde (10): This compound was synthesized by modification of the procedure of [31].…”

“…The NMR data are consistent with that reported in the literature [31] 10-Methoxy-9-phenanthrenealdehyde: This compound was synthesized by modification of literature methods [31]. The resulting light brown solid residue was purified by flash column chromatography on silica gel, using an eluent gradient of n-hexane/dichloromethane/(2:1), then (1:1) and finally (1:4) to give a white solid (0.83 g, 67% 10-Hydroxy-9-phenanthrenealdehyde (10): This compound was synthesized by modification of the procedure of [31]. A flame dried 50 mL round-bottom flask equipped with a magnetic stirrer and a nitrogen inlet was charged with a solution of 10-methoxy-9-phenanthrenecarboxaldehyde (0.61 g, 2.6 mmol) in dry dichloromethane (25 mL) and cooled to −10 • C. Under nitrogen atmosphere was added a solution of BBr 3 (6.0 mL, 1.0 M solution in dichloromethane) and stirred at 0 • C for 15 min and at room temperature for 1.5 h. The reaction mixture was poured onto ice in 1.0 M HCl (30 mL).…”

“…The crude product was purified by flash column chromatography on silica gel using dichloromethane to afford pure product as a pale yellow solid (0.59 g, 56%). The NMR data are consistent with that reported in literature [31]. HRMS-ESI calculated for C 12 H 10 O 2 [M + H] + 186.0681, found 186.0645.…”

“…The starting material 3-methoxy-2-naphthaldehyde was prepared according to the procedure described by Legouin et al [31]. The crude product was purified by flash column chromatography on silica gel using dichloromethane to afford pure product as a pale yellow solid (0.59 g, 56%).…”

“…HRMS-ESI calculated for C 11 H 8 O 2 [M + H] + 172.0524, found 172.0538. 9-Methoxyphenanthrene: This compound was synthesized according to previously reported procedure [31]. The light amber solid was purified by flash column chromatography on silica gel, using dichloromethane/ n-hexane (2:1) to afford the pure product as off white solid (1.2 g, 91%).…”