Novel rearrangement of twisted 2,4-di-alkyl 2-trans-4-trans pentadienals: An approach to cyclopentenones based on molecular mechanical consideration
✍ Scribed by Haru Ogawa; Yoshinari Taketugu; Taiji Imoto; Yōichi Taniguchi; Hidefumi Kato
- Publisher
- Elsevier Science
- Year
- 1979
- Tongue
- French
- Weight
- 250 KB
- Volume
- 20
- Category
- Article
- ISSN
- 0040-4039
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✦ Synopsis
Rearrangement of 2,4-di-mpentadienals IVa-d was described as a consequence of the successive alkyl substitutions on the C-2 and C-4 positions. 1 H-FT nmr spectroscopy suggested that the reaction involves ketene VI&& as an intermediate. Hydrogen-hydrogen repulsive interactions occurred in annulenes (for example, z and ula) not only specify the thermodynamic stabilities of the molecules, but they are also vital for the determination of the dynamic equilibrium among possible geometrical isomers lb) . Similar circumstances may arise, when bulky groups are introduced on linear conjugated system L Molecular mechanical considerations suggest that &becomes favoured than b, and cyclization of & may be induced, if a suitable reaction path is opened for the transformation. As model reaction, we report novel rearrangement of S-(p-nitrophenyl)-2,4-di-alkyl-pentadienals IVa_d to the corresponding cyclic enones && and their tautomers Xa_d and XIa_d (see Scheme 1).