[91550-25-3] · C36H27NO3S · Tetraphenylcyclopentadienone Oxime O-Tosylate · (MW 553.71)
(electrophilic aminating reagent for Grignard reagents1)
Solubility: sol ether, THF.
Preparative Methods: Tetraphenylcyclopentadienone (commercially available) reacts with Hydroxylamine in pyridine to yield the corresponding oxime,2 and the oxime reacts with p-Toluenesulfonyl Chloride in an acetone-H2O basic solution to yield the oxime tosylate.3
The addition of organometallic reagents to oximes4 has found limited applicability due to their low electrophilicity and a-deprotonation requiring the use of a considerable excess of organometallic reagent (eq 1). There are various scattered reports of reactions of Grignard reagents and organolithiums with oximes that furnish amines, amino acids, aziridines, b-amino alcohols, and other products.5 Ketoximes and their O-substituted derivatives can also serve as electrophilic aminating reagents for Grignard reagents and organolithiums (eq 2).5 So far, acetoxime,6,7 butanone oxime,6 cyclohexanone oxime,8 benzaldoxime,9 isobutyrophenone oxime,10 Acetoxime O-(2,4,6-trimethylphenyl)sulfonate,11 and tetraphenylcyclopentadienone oxime O-tosylate1 have been used for amination of Grignard reagents and organolithiums.
Tetraphenylcyclopentadienone oxime O-tosylate reacts with aryl Grignards and lithiums to give the corresponding imines in good to excellent yields, which are then converted to arylamines by reaction with excess hydroxylamine (eq 3).3
A typical experimental procedure is as follows. The aminating reagent (1 equiv) is added to the aryl Grignard reagent (7 equiv) in THF at -78 °C and the mixture is stirred at -78 °C for 45-90 min. The imine is extracted with benzene, crystallized from benzene-heptane (1:3), and then stirred at rt for 2 h with excess hydroxylamine in aqueous pyridine. The oxime is precipitated on acidification, and, following base treatment, the amine is isolated. Alkyllithiums and Grignard reagents have also been reported to react with the tosylate to yield the corresponding imine, but yields have not been reported.
Significant features of this method are the good yields of aryl amines compared to those obtained by the use of other ketoximes as electrophilic aminating reagents, and the mode of the activating the aminating reagent O-tosylhydroxylamine by attacking an auxiliary group (tetraphenylcyclopentadienyl moiety), which then can be removed and efficiently recycled through the sequence.
Ankara University, Turkey