Conformational Chiral Recognition in a Simple Urea

Abstract

Urea 4 was unexpectedly isolated from the reaction of benzylamine with tosylate ester 1. Crystallisation of an inseparable mixture of hemiaminal 3 and 4 from ethanol provided crystals of 4 suitable for single crystal X-ray diffraction (C 15 H 16 N 2 O, monoclinic, space group Ia, a 5 22.9800(16), b 5 4.618 (9), c 5 24.059(10) Å , b 5 99.91(3)8, D c 5 1.269 g cm 23 , Z 5 8 and 2703 observed reflections. Refinement terminated with R 1 5 0:0876; wR 2 5 0:1953 ðI > 2sIÞ and R 1 5 0:2154; wR 2 5 0:2445 (all data). These revealed that the unit cell contained only two of the possible three conformers of 4. Both the predictable achiral conformer 4a and the unexpected chiral conformer 4b appear to be independent of one another. Each conformer is linked into an independent polymeric chain via an array of hydrogen bonds between the Lewis basic oxygen lone pairs and N -H donors of the urea.

An Efficient Route to Symmetrically and Unsymmetrically Substituted Azamacrocyclic Ligands

“…After cooling to room temperature, the inorganic salts were removed by filtration and the filtrate evaporated under reduced pressure to leave a yellow solid which was purified by column chromatography on silica gel [petroleum ether (40:60)/ethyl acetate, 3:1] to give 7a (20 mg, 3%) as a white solid. In addition to 7a the following compounds could also be isolated: 5a (160 mg, 28%), 8 (20 mg, 2%), 9a (60 mg, 11%), 10 (200 mg, 27%), 11 (traces) [33,34] and 12 (90 mg, 15%).…”