SYNTHESIS AND PROPERTIES OF FIRST-GENERATION AND 2ND-GENERATION CHIRAL DENDRIMERS WITH TRIPLY BRANCHED UNITS - A SPECTACULAR CASE OF DIASTEREOSELECTIVITY

Chiral triols (which may be considered as derivatives of tris(hydroxym ethyl)methane), without (3-5) and with aliphatic (6) or aromatic (7) e longating units, and the 1st- and 2nd-generation benzylic branched bro mides, 17, 18, 23, 24, 29, and 30 are subjected to Williamson etherifi cation conditions (NaH in THF). This gave the first 'fully chiral' den drimers, with triple branching and with a stereogenic center at each a nd every branching point (including the central building block; see 33 -42, 44, and 46-49). Higher than Znd-generation dendrimers of this typ e could not be prepared. Certain combinations of diastereoisomeric ?nd -generation branched bromides, 23, 24, 29, and 30, and enantiomeric ce nter-piece triols, 3 and 4, would smoothly react to give the desired d endrimers (e.g., 44, and 46-49) and others would not, with the reactio ns stopping at the dendritic alcohols containing only two branches (e. g., 45, and 50-53; see Schemes 4 and 5). Considering the distance at w hich the intermediate diastereoisomeric 'doubly coupled' dendritic alc ohols differ in their configuration, this diastereodifferentiation or molecular recognition phenomenon (discovered by trying to prepare only 8 out of 2(39) possible diastereoisomers!) is a most surprising resul t. All compounds were fully characterized, and the 2nd-generation dend rimers, e.g., 38, 40, and 47 with and without elongation were shown to be monodisperse and without defects, by MALDI-TOF mass spectroscopy ( cf. Fig. 4). A simple, unambiguous nomenclature for identification of the novel dendritic compounds is proposed and applied in the Exper. Pa rt.