Preparation and structure-chiroptical relationships of tartaric acid-based layer-block chiral dendrimers

Two optically active, diastereoisomeric, first generation layer-block dendrimers 1 and 2 have been prepared by a convergent synthetic procedure. These chiral, layer-block dendrimers utilize 4-tert-butylphenoxy moieties as the surface groups and phloroglucinol as the branching junctures. Two different chiral units, which are derivatives of (D)- and (L)-tartaric acid, serve as the chiral linkers between the surface group and the branching juncture, or between two branching junctures. The first layer-block dendrimer 1 has an outer chiral layer made up of six (L)-tartrate derived units and an inner chiral layer of three (D)-tartrate derived units. The second layer-block dendrimer 2 has an outer shell consisting of three (D)- and three (L)-chiral units and an inner shell of three (D)-chiral units. The molar rotation of these structurally flexible, low generation dendritic compounds is proportional to the number of chiral tartrate units in excess, with the chiroptical effect of a (D)-tartrate derived chiral unit cancelling that of an (L)-tartrate derived unit on a 1:1 basis. Circular dichroism studies, however, reveal that this cancellation effect is more effective when both the (D)- and (L)-chirons are situated within the same layer.