Free and Polymer-Bound Tricyclic Azaphosphatranes HP(RNCH(2)CH(2))(3)N(+): Procatalysts in Dehydrohalogenations and Debrominations with NaH.
The commercially available nonionic base P(CH(3)NCH(2)CH(2))(3)N (1a) was shown earlier to be superior to DBU as a stoichiometric reagent for the conversion of primary and secondary alkyl halides to alkenes (Arumugam, S.; Verkade, J. G. J. Org. Chem. 1997, 62, 4827). The precursor cation HP(CH(3)NCH(2)CH(2))(3)N(+) (2) to 1a, which is more stable and less expensive, is reported herein to be an efficient procatalyst for these reactions and also for the debromination of vicinal dibromides using NaH as a relatively inexpensive stoichiometric hydride source in CH(3)CN at room temperature. In dehydrohalogenations requiring more than ca. 10 h, the CH(2)CN(-) ion also acts as a base. By itself, NaH does not function well or at all under the same conditions. A catalytic cycle is proposed in which hydride deprotonates cation 2 liberating catalytic 1a. The cations HP(HNCH(2)CH(2))(3)N(+) (3) and HP[N(polymer)CH(2)CH(2)]N(CH(2)CH(2)NH)(2)(+) (4) are also shown to function as procatalysts for the efficient dehydrohalogenation of RX and for the debromination of vicinal dibromides. The preparation of the heterogeneous procatalyst 4(OTf) is also described.
Liu
Xiaodong
X
Department of Chemistry, Iowa State University, Ames, Iowa 50011.
Verkade
John G.
JG