Zusammenfassung
The new helical compounds 1–3 have been synthesized. 1 and 2 are separated into the enantiomers by chromatography on cellulose triacetate. The rotatory powers are high: e.g., [α]math image = 2096 for 1. The racemization/ring inversion barriers range between 115 and 125 kJ/mol. X-ray analyses of 1–3 reveal different torsional angles between the rings ABC from 3.6 to 10.4°. They are compensated ...
Zusammenfassung
The new helical compounds 1–3 have been synthesized. 1 and 2 are separated into the enantiomers by chromatography on cellulose triacetate. The rotatory powers are high: e.g., [α]math image = 2096 for 1. The racemization/ring inversion barriers range between 115 and 125 kJ/mol. X-ray analyses of 1–3 reveal different torsional angles between the rings ABC from 3.6 to 10.4°. They are compensated through the different interplanar angles of A and C with the plane B in such a way that the distance d between the intraanular C-Atoms in all compounds 1–4 is similar (2.57–2.60 Å). Correspondingly, the δ(Hi) values of 1–4 are found to differ only slightly (5.32–5.67 ppm). A determination of the absolute conformation using Bijvoets method shows (−)-2 (λ = 546 nm) to be the P-helix, and ( + )-2 the M-helix.
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