Unusual Totally Selective Cyclodimerization of Epoxides: Synthesis of a Pair of Diastereoisomers of Enantiopure 2,5‐Disubstituted‐1,4‐Dioxanes with C 2 Symmetry

The synthesis of the C 2 ‐symmetrical (2 R ,5 R )‐ and (2 S ,5 S )‐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 (2 R ,1′ S )‐ or (2 S ,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.