[83575-89-7] · C14H16NO2P · N,N-Dimethyl-O-(diphenylphosphinyl)hydroxylamine · (MW 261.28)
Physical Data: mp 129-131 °C.2
Solubility: slightly sol THF, diethyl ether; sol CHCl3, CH2Cl2.
Analysis of Reagent Purity: 1H NMR (CDCl3, ppm): 2.78 (s, 6 H, Me2N), 7.36-8.18 (m, 10 H, phenyl).
Preparative Methods: (1) to 9.67 g (100 mmol) N,N-dimethylhydroxylamine suspended in 80 mL CH2Cl2 are added dropwise at -20 °C under stirring 20.3 g (200 mmol) triethylamine. Then 23.7 g (100 mmol) diphenylphosphinyl chloride dissolved in 80 mL CH2Cl2 are added within 1 h. After extraction of the salts with ice water (2-3 times) the solution is dried (MgSO4), and the solvent removed. Recrystallization from diethyl ether affords 17.7 g (68%) colorless crystals of N,N-dimethyl-O-(diphenylphosphinyl)hydroxylamine (1).2,3
(2) To a solution of 2.00 g (4.60 mmol) bis(diphenylphosphinyl) peroxide in 50 mL CH2Cl2, cooled to -60 °C, is added under stirring within 1 h 10.8 mL of a 0.86 M solution of dimethylamine in CH2Cl2 (9.20 mmol dimethylamine). The reaction is continued overnight under warming to 0 °C. Then the organic layer is washed 4 times with cold water, dried, and the solvent removed. After crystallization from diethyl ether, 1.18 g (98%) (1) are isolated. This is a general procedure which allows the preparation of other N,N-di- as well as N-alkyl-O-(phosphinyl)hydroxylamines.4
Handling, Storage, and Precautions: stable for more than a year if stored at -30 °C.
Reaction of cyclopentadienyllithium (2) with (1) leads to an equilibrium dominated by N,N-dimethylaminocyclopentadiene (3b) (eq 1).3 Aminocyclopentadienes are not easily accessible by methodologies other than electrophilic amination. For this amination reaction, N,N-Dimethyl-O-(methylsulfonyl)hydroxylamine3 and N,N-dimethyl-O-(diphenoxyphosphoryl)hydroxylamine3 can also be used.
Reaction of (3) with n-Butyllithium affords N,N-dimethylaminocyclopentadienyllithium (4), which is a precursor for the preparation of the corresponding metallocenes, e.g. (5) (eq 2),3 and others.5
(1) aminates lithiated O-(trimethylsilyl) aldehyde cyanohydrins (8) (eq 4), derived from aromatic aldehydes (6) and Cyanotrimethylsilane via the corresponding cyanohydrins (7) (eq 3).6
Since (9) (which is not isolated) is easily hydrolyzed (2 N HCl) to the amides (10), the reaction sequence (6) -> (10) amounts to a mild and selective oxidation of an aromatic aldehyde to an amide.
(1) (or its amination equivalent N,N-dimethyl-O-(methylsulfonyl)hydroxylamine) reacts with metallated alkynes.7 Although the reactions with RC&tbond;CLi and RC&tbond;CMgX do not lead to ynamines, the cuprates (11), prepared by one of three methods (eqs 5-7), do give ynamines.
(11) transfers only two R groups onto (1) (eq 8). The R groups can be Ph, n-Pr, n-Bu, n-C6H13, Cy, t-Bu, Me3Si, or PhS, for example. The yields of the ynamines are usually in the range of 60-70%.
Philipps-Universität Marburg, Germany