[61024-99-5] · C13H12AsLiO · (Diphenylarsinyl)methyllithium · (MW 266.11)
(indirect nucleophilic halomethylation2 and haloalkylation3 of aldehydes, ketones, alkyl halides, and epoxides; synthesis of 2-hydroxy-1,2l5-oxarsolanes,1,4 1,2-bis(diphenylarsinyl)ethane, 1,2-bis(diphenylarsino)ethane (
diars), and 1-diphenylarsino-2-(diphenylarsinyl)ethane5)
Solubility: sol THF.
Preparative Method: quantitatively formed as a yellow solution in THF by treating the easily accessible (diphenylarsinyl)methane6 with LDA at -40 °C (eq 1).
Handling, Storage, and Precautions: handle and store the THF solution of Ph2As(O)CH2Li under N2 or Ar; Ph2As(O)Me (mp 153-154 °C) is stable in air but toxic. Use in a fume hood.
HalCH2Li and HalCH(Alk)Li would be interesting reagents for nucleophilic halomethylation and a-haloalkylation, but they are quite unstable due to carbene formation. Ph2AsCH2Li7 is an attractive synthetic equivalent for HalCH2Li, but Ph2As(O)CH2Li is more accessible and more reactive. Treatment of this reagent with electrophiles (aldehydes, ketones, alkyl halides) followed by Lithium Aluminum Hydride and then with halogen (Br2, I2) or Thionyl Chloride affords halogen compounds (e.g. b-hydroxy alkyl halides) in preparatively useful yields (eq 2; R = H).2 The yield determining step is the reaction with the electrophile, according to eqs 3 and 4.
Like Ph2As(O)Me, the higher homologs (prepared as in eq 3) can be lithiated at the methylene group a to the As atom by Lithium Diisopropylamide. The resulting compounds provide entry to functionalized hydrocarbons according to eq 2 (R = Alkyl).3 Sulfuryl Chloride is particularly useful as a reagent for replacing the diphenylarsino group by chlorine. Also the methine group of s-butyldiphenylarsine oxide is lithiated by LDA (80%). a-Lithiated alkyldiphenylarsine oxides react extremely diastereoselectively with benzaldehyde or acetophenone.3b
The treatment of terminal epoxides with Ph2As(O)CH2Li and subsequently with H2O leads to 2,2-diphenyl-2-hydroxy-1,2l5-oxarsolanes (eq 5), which are smoothly reduced by LiAlH4 to g-hydroxy alkyl arsines. These undergo halogenolysis to give g-hydroxy alkyl halides.1,4
Ph2As(O)CH2Li reacts with Copper(II) Chloride to give 1,2-bis(diphenylarsinyl)ethane (64%), which is quantitatively reduced by LiAlH4 to 1,2-bis(diphenylarsino)ethane, the important ligand
diars for transition metals (eq 6). Sodium Borohydride can be used to obtain the corresponding monooxide (88%).5
Universität Münster, Germany