ABSTRACT
The combination of SmI2 and the conjugate base of triethylurea (TEU-) has been shown to favor the cyclization of unsaturated halides over direct reduction to a much greater extent than other SmI2-based reductants. Aryl, heteroaryl, and alkyl halides (X = Br, Cl, F) readily undergo heterocyclization and carbocyclization in the presence of SmI2/TEU-.
ABSTRACT
A novel mode of SmI2 activation has been developed using ureates as reaction promoters. Several ureates formed by treatment of the corresponding ureas with n-BuLi have been shown to activate SmI2 to a substantial extent toward the reduction of 1-chlorodecane. Complexes formed from SmI2 and various ureates have been shown to be useful for the reduction of a variety of organohalides, including substrates of low reactivity such as aryl fluorides. Because of ease of synthesis and low molecular weight, the conjugate base of triethylurea (TEU(-)) was of primary focus. Visible spectroscopy and reactivity data are consistent with the hypothesis that the same complex is being formed when SmI2 is combined with either 2 or 4 equiv of TEU(-), in spite of the greater reactivity of SmI2/4 TEU(-) with some alkyl halides. We propose that the active reductant is an N,O chelate formed between SmI2 and 2 equiv of TEU(-).
ABSTRACT
The electrochemical and spectrophotometric characterization of the complex formed from samarium diiodide and 4 equiv of tripyrrolidinophosphoric acid triamide (TPPA) is presented. Kinetic studies indicate that the SmI(2)/TPPA complex possesses reactivity greater than the complex formed between samarium diiodide and 4 equiv of HMPA. Examples of the use of SmI(2)/TPPA in synthesis are presented.
