An asymmetric synthesis of tetra-substituted cyclobutanes involving an organocatalytic, stepwise [2+2]-cycloaddition is described. The secondary-amine-catalyzed method allows for the hetero-dimerization of two different cinnamic-acid-derived sub-units, opening a novel one-step assembly to densely functionalized, head-to-tail coupled dimeric cyclobutanes in high enantiomeric excess. A series of selective synthetic interconversions in these sensitive cycloadducts is also described.
Keywords: asymmetric synthesis; cyclobutanes; lignan dimers; organocatalysis.
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