91049-37-5Relevant academic research and scientific papers
Dramatic Yield Increase in Cyclizations Leading to Strained Heterocycles of Medium Ring Size
Ostrowicki, Andreas,Voegtle, Fritz
, p. 1003 - 1004 (2007/10/02)
By careful choice of the cyclization conditions (solvent, concentration of cesium hydroxide, high dilution) several strained heterocyclic metacyclophanes could be obtained in dramatically increased yields.The favorable effect of cesium hydroxide on the yield was proven.
Novel Family of Heterocyclic Strained Helices. Cesium-Assisted Syntheses and Conformational and Chirooptical Properties and Geometries
Meurer, Kurt,Voegtle, Fritz,Mannschreck, Albrecht,Stuehler, Georgine,Puff, Heinrich,Roloff, Albrecht
, p. 3484 - 3489 (2007/10/02)
The syntheses of 1-oxa-10-thiametacyclophane (1) and 1-thia-10-(p-toluolsulfonyl)-10-azametacyclophane (2) have been achieved for the first time by cesium-assisted high-dilution methods.Prior to application of the cesium effect, 1 and 2 were not available.In the NMR spectra, the intraannular hydrogens Hi of both 10-membered rings (Figure 1) are strongly shifted upfield.Both molecular helices 1 and 2 can be resolved (1) or enantiomerically enriched (2) by inclusion chromatography with triacetyl cellulose.The optical rotations are high, i.e. RT365=1542, Δε242=81 for (-)-1 ( in 1,4-dioxane).The absorption spectra and the circular dichroisms of 1 and 2 ( Figures 2 and 3), as well as the comparision with exocyclic-substituted metacyclophanes like 6-11, give insight into the dependence between structure and helicity of these 10-membered rings.The absolute configurations of 1 and 2 can be presumed from circular dichroic correlations ( Figure 4).The kinetic parameters for the ring inversions of 1 and 2, accessible by measuring the rates of racemization or interconversion, were determined to be ΔG(excit.)INT=123.3 kJ mol-1, kINT=4.87*10-5 s-1 (100 deg C) for 1 and ΔH(excit.)INT=130.7 kJ mol-1, kINT=5.40*10-6 s-1 (102 deg C) for 2.The high barrier of racemization of 2 is discussed.X-ray analyses of 1 and 2 disclose for the first time exact data about the C-N, C-O, and C-S bond lenghts as well as the transannular distances d between C(Hi) and C'(Hi) and the bond angles in this new type of two-bladed propellers.The geometries and helicities of 1 and 2 are illustrates and compared by using the torsion angles α-δ (Figure 7).
