Ring-Opening Reactions of 2-Lithio-1,3-dithiane and 2-Lithio-1,3,5-trithiane with Carbene Complexes of Chromium and Tungsten

✍ Scribed by Prof. Dr. Helgard G. Raubenheimer; Prof. Dr. Ernst Otto Fischer; Priv.-Doz. Dr. Ulrich Schubert; Prov.-Doz. Dr. Carl Krüger; Dr. Yi-Hung Tsay

• Publisher: John Wiley and Sons
• Year: 1981
• Tongue: English
• Weight: 219 KB
• Volume: 20
• Category: Article
• ISSN: 0044-8249
• DOI: 10.1002/anie.198110551

✦ Synopsis

the line-shape changes allow the detection of two different dynamic processes, which may be assigned to inhibited rotations about the partial C C and C N double bonds of the E-isomers (Scheme 2).

Above ca. 0°C conversion into the isomer with Z-configurated CC double bond, which contains an intramolecular hydrogen bond (&,=9.7 in CD2C12 at OOC), is observed within a few minutes; in comparison, &H =4.9 ppm for the E-isomer. Once again the chemical shifts for the Zisomer in solution are similar to those of the E-isomer in the crystal. As was discussed for (I), changes in the chemical shifts are essentially due to hydrogen bonding. After allowing the solution to stand at room temperature for several days the equilibrium lies at 7% Eand 93% Z-isomer.

A vinylogous amide, in which the N-methyl group in (2) is replaced by a n N-phenyl group, behaves in a completely