Hydroxy-Functionalized Dendritic Building Blocks

A convenient and practical multi-gram procedure for the synthesis of second- (G2; 4a, 5a, 5d) and third-generation (G3; 6a) dendrons with orthogonally protected functional groups in the periphery (hydroxy) and at the focal point (carboxylic acid) is described. It uses the amply available first-generation dendrons with amine and carboxylic ester functions (1) and tetrahydropyranyl-protected hydroxy and carboxylic acid functions (2b, 3), respectively, which are connected via amides by peptide methods. Purification is either done by recrystallization or simple filtration through silica gel and yields the products as analytically pure materials on a several-gram scale (even for G3). ‘The dendrons’ protective groups are proven to be orthogonal (500-MHz NMR) which makes them useful components (building blocks) of a future dendron construction kit for a versatile synthesis of, for example, dendronized polymers.