Synthesis and chiroptical properties of amphiphilic dendrimers based on 2,3-dihydroxybenzyl alcohol

The syntheses and chiroptical properties of amphiphilic dendrimers based on 2,3-dihydroxybenzyl alcohol up to the third generation are described. Water-solubility is imparted to the dendrimers using a selective palladium-catalyzed deprotection of allyl ester terminal groups. Circular dichroism studies indicate that a transfer of chirality from the central core to the achiral branch segments does not occur in any of the dendrimers in THF. However, a temperature-dependent Cotton effect associated with the 2,3-dialkoxybenzyl ether branching subunit appears at the first generation in water consistent with a transfer of chirality from the chiral core to the dendrons. This effect disappears at the second and third generations suggesting greater conformational flexibility at higher dendrimer generation. The increased flexibility at higher dendrimer generation is rationalized by a decrease in hydrophobic compression at higher dendrimer generation. This work highlights the effect of asymmetric branching and solvent-induced compression in restricting the conformational mobility of dendrimers.