𝔖 Bobbio Scriptorium
✦   LIBER   ✦

Positional and Facial Selectivity in Diels-Alder Reactions of (−)-(aS,7S)-Colchicine: Synthesis of Novel Analogues of the Alkaloid

✍ Scribed by Brecht, René ;Haenel, Frank ;Seitz, Gunther ;Frenzen, Gerlinde ;Pilz, Astrid ;Massa, Werner ;Wocadlo, Sigrid

Publisher
John Wiley and Sons
Year
1997
Tongue
English
Weight
773 KB
Volume
1997
Category
Article
ISSN
0947-3440

No coin nor oath required. For personal study only.

✦ Synopsis

Abstract

Positional and facial selectivity in Diels‐Alder reactions of several hetero‐ and carbodienophiles with (−)‐(a__S__,7__S__)‐colchicine (1) has been examined. In all cases, cycloaddition occurred with high positional selectivity at the 8,12‐positions of the alkaloid and preferentially from the diene face syn to the allylic substituent at the stereogenic center C‐7. The observed high π‐facial diastereoselectivity is independent of the polarity of the solvent used and is therefore probably a consequence of steric factors. The structures of the Diels Alder‐adducts of 1 with singlet oxygen, N‐phenyl‐1,2,4‐triazolinedione (PTAD) and trans‐cyclooctene, 4,5, and 15, respectively, were assigned on the basis of spectral data and verified by X‐ray crystallography.

📜 SIMILAR VOLUMES

Chemistry of Opium Alkaloids, XLIII – A
Chemistry of Opium Alkaloids, XLIII – A PM3 Computational Approach to the Selectivity in the Diels-Alder Reactions of Thebaine and Analogues with Methyl Propenoate
✍ Baas, Jan M. A. ;Woudenberg, Richard H. ;Maat, Leendert 📂 Article 📅 1997 🏛 John Wiley and Sons 🌐 English ⚖ 603 KB

## Abstract Geometrically fully‐optimized transition structures are calculated for the Diels‐Alder adducts of methyl propenoate and the 3‐demethoxy derivatives of the dienes thebaine, 6‐demethoxythebaine, 5β‐methylthebaine, and 5β‐methyl‐6‐demethoxythebaine using the semiempirical PM3 method. The n