194495-06-2Relevant academic research and scientific papers
Siloxy effect on intramolecular cyclization of tungsten-η1-siloxypropargyl complexes: Formation of 2,5-dihydrofurans versus γ-lactones
Shieh, Shwu-Ju,Fan, Jang-Shyang,Chandrasekharam, Malapaka,Liao, Fen-Ling,Wang, Sue-Lein,Liu, Rai-Shung
, p. 3987 - 3992 (1997)
Treatment of tungsten-η1-4-(triethylsiloxy)propargyl and η1-4-(tripropylsiloxy)propargyl compounds 8a-d and 9a-d with CF3CO2H in cold CH2Cl2 yielded a mixture of tungsten η1-2,5-dihydrofurans 1a-d and η3-syn-γ-lactones 4a-d. The product ratios depend on the types of alkyl and siloxy substituents of the propargyl ligand; η1-2,5-dihydrofurans 10a-d were formed in significant amount when the substituent is a secondary alkyl group. This cyclization pathway is in sharp contrast to our previous report that the dimethyl-tertbutylsiloxy group yielded only η3-syn-γ-lactones 4a-d. To validate this reaction on a complex system, we prepared the chiral tungsten-η1-4-(triethylsiloxy)propargyl species 12b, which ultimately gave optically active tungsten η1-2,5-dihydrofuran 13 in 68percent yields. In connection with our previous report, we elaborated three types of cyclization reactions on chiral tungsten η1-propargylic triols 12a-c, to afford chiral η1-2,5-dihydrofurans and unsaturated γ- and δ-lactones in reasonable yields.
