Unusual totally selective cyclodimerization of epoxides: Synthesis of a pair of diastereoisomers of enantiopure 2,5-disubstituted-1,4-dioxanes with C-2 symmetry

摘要

The synthesis of the C-2-symmetrical (2R,5R)- and (2S,5S)-2,5-bis-[(S)-1-(dibenzylaminoalkyl)]-1,4-dioxanes 1 or 2 in enantiopure form is reported. Compounds 1 and 2 were obtained by a completely selective and unusual cyclodimerization of chiral (2R,1'S)- or (2S,1'S)-2-(1-aminoalkyl)epoxides 3 or 4 promoted by a mixture of diisopropylamine and boron trifluoride-diethyl etherate complex. The structure of the obtained dioxane was established by single-crystal X-ray diffraction analysis. A mechanism has been proposed to explain this transformation.