1,3-Dipolar cycloadditions of diphenyldiazomethane to thioketones: Rate measurements disclose thiones to be superdipolarophiles
✍ Scribed by Rolf Huisgen; Elke Langhals
- Publisher
- John Wiley and Sons
- Year
- 2006
- Tongue
- English
- Weight
- 226 KB
- Volume
- 17
- Category
- Article
- ISSN
- 1042-7163
- DOI
- 10.1002/hc.20262
No coin nor oath required. For personal study only.
✦ Synopsis
1,3-Dipolar cycloadditions of diphenyldiazomethane to thioketones afford 2,5-dihydro-1,3,4thiadiazoles 8, which rapidly lose N 2 . The liberated thiocarbonyl ylides 10 furnish thiiranes 9 by electrocyclic ring closure. The rate constants, measured by spectrophotometry (DMF, 40 • C) for 16 cycloaliphatic and aromatic thioketones and one cyclic trithiocarbonate, stretch over five powers of 10 with fluorene-9-thione at the top and 2,2,5,5-tetramethylcyclopentanethione at the bottom. Electron-releasing substituents decrease the cycloaddition rate of thiobenzophenone; thus, the ambiphilic diphenyldiazomethane reacts as nucleophilic partner with the electrophilic thioketone. The influence of substituents and ring size on the reactivity of cycloalkanethiones, which are sterically hindered by two gem-dimethyl groups, will be discussed.