Two New Valence Isomers of [12]Annulene

✍ Scribed by Priv.-Doz. Dr. G. Schröder; Dr. W. Martin; Dr. H. Röttele

• Publisher: John Wiley and Sons
• Year: 1969
• Tongue: English
• Weight: 226 KB
• Volume: 8
• Category: Article
• ISSN: 0044-8249
• DOI: 10.1002/anie.196900692

✦ Synopsis

3a), X = Br (3b), X = COOH Keeping equimolar amounts of (3b) and brucine in ethanol/ methanol (1 : 1-1 : 2 v,'v) for some time gives a 60 % yieldC71 of a crystalline brucine salt that shows rapid mutarotation in acetone at 20.5 O C (ty2 = 200 sec; extrapolation of the specific rotation to to gives [ C C ] : ; ~ = +87 O, changing to -43 O, c = 0.013 g/ml).

The dextrorotatory acid can be obtained by dissolving this salt as fast as possible in acetone at -2OOC and precipitating it rapidly with 2N HCI. Solutions of (+)-(3h) in acetone racemize at +20.5 "C with a half-life period of 195 sec; [ o ( ] : : b 5 was +135" after 105 sec (extrapolated to to: [a]::k5 = +190 O, c = 0.02 g/ml). Thence the free enthalpy of activation for ring inversion of (3b) is calculated to be AG.$,, = 20.8 kcal/mole, i.e., ( 36) is much more mobile than comparable systems 111.