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Kinetik und stereochemischer Verlauf der thermischen Umlagerung der vier stereoisomeren Propenyl‐(but‐2′‐enyl)‐äther
Author(s) -
Vittorelli Piero,
Hansen HansJürgen,
Schmid Hans
Publication year - 1975
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19750580508
Subject(s) - chemistry , propenyl , steric effects , ether , stereochemistry , medicinal chemistry , diastereomer , gas phase , organic chemistry
The gas‐phase rearrangement of (1Z, 2′E)‐, (1Z, 2′Z)‐, (1E, 2′E)‐, and (1E, 2′Z)‐ propenyl but‐2′‐enyl ether (Z, E)‐, (Z, Z)‐, (E, E)‐, and (E, Z)‐1) into erythro‐ and threo‐2, 3‐dimethyl‐pent‐4‐en‐al (erythro‐ and threo‐2) was investigated over a temperature range from 142,5° to 190,0° at 20–35 Torr (for kinetic data and activation parameters see table 2). All four stereoisomeric ethers 1 rearrange preferentially via a chair‐like transition state C into the aldehydes 2 (ΔΔG ≠ (160°) = 2,5–2,7 kcal/mol for B – C (B = boat‐like transition state). The relative rates (k rel ) for (Z, Z)‐1, (Z, E)‐1, (E,Z)‐1, and (E,E)‐1 at 160° are 1,0, 2,9, 4,3 and 9,0 respectively (see table 5). Taking into account the relative enthalpies of the ethers 1 and the steric interaction in the C transition state of the ethers 1 (see table 6), k rel values can be estimated. They are in good agreement with those observed (see table 5).