Resolution of sterically overcrowded ethylenes; a remarkable correlation between bond lengths and racemization barriers.
作者:Ben L. Feringa、Wolter F. Jager、Ben de Lange
DOI:10.1016/s0040-4039(00)78887-3
日期:1992.5
The synthesis and resolution of 2-methyl-9H-thioxanthene-9-(9H-thioxanthen-9-ylidene) 1 and related structures 2-5, being the first examples of thermally stable optically active sterically overcrowded ethylenes, are reported. Substitution of the sulfur atom in the thioxanthene part of 1 with an X group (2, X = C(CH32; 3, NCH3 4, O) results in a change in racemization barrier (1, 27.4 kcal.mol−1; 3
Sterically overcrowded alkenes; a stereospecific photochemical and thermal isomerization of a benzoannulated bithioxanthylidene
作者:Ben L. Feringa、Wolter F. Jager、Ben de Lange
DOI:10.1039/c39930000288
日期:——
Enantiomericallypure sterically overcrowded 12H-benzo[a]thioxanthenyl-12-(2-′methyl-9′H-thioxanthene-9′-ylidene) shows a Stereospecific photochemical and thermal isomerization, of the P-trans into the M-cis isomer (andvice versa), with a large thermal isomerization barrier (ΔG‡= 28.6 kcal mol–1)(1 cal = 4.184 J), making this type of molecule especially suitable as the key structural unit for applications
Sterically overcrowded alkenes; synthesis, resolution and circular dichroism studies of substituted bithioxanthylidenes
作者:Wolter F. Jager、Ben de Lange、Anne Marie Schoevaars、Fré van Bolhuis、Ben L. Feringa
DOI:10.1016/s0957-4166(00)80349-3
日期:1993.7
Bithioxanthylidenes with small substituents at positions 2 and 2' have been synthesized and resolved by chiral HPLC. The X-ray molecular structure of 9-(2'-methyl-9'H-thioxanthene-9'-ylidene)-9H-xanthene (17) confirms the folded form of these molecules. UV and CD studies of several bithioxanthylidenes are presented. The CD spectra of these molecules can be described qualitatively by subtracting the CD spectra of both differently sensed helices (M and P) present in the molecule, which can be distinguished by the substituents at positions 2 and 2'.