Elucidating factors leading to acidolytic degradation of sterically strained oligoether dendrons

Abstract

While steric hindrance can be particularly large in dendritic molecules, it is usually implicated with difficulties in the synthesis of higher generation structures and restricted access of reagents, including bond-cleaving agents, to the dendritic interior. A different situation, where the steric hindrance is translated into a steric strain within the dendritic molecule and, consequently, causes enhanced decomposition of the dendron-containing structure, has only occasionally been reported and exclusively for dendronized polymers. In this work we describe post-synthetic cleavage of sterically congested third-generation oligoether dendrons from solid supports, followed by their disassembly into monomeric building blocks under acidic conditions. This disassembly was monitored by H NMR, revealing the intermediate fragment structures and the exact order of bond cleavage within the dendritic molecule. These conclusions were supported by MS analysis of the cleavage mixtures. Though distinguishing between steric and electronic reasons of molecular disassembly can be a challenging task, we were able to analyze these factors separately by monitoring the dendron disassembly and comparing the rates of "decay" of parent dendrons and their fragments. This comparison reveals that while the electron donation of the steric congestion-inducing alkyl substituents is a prerequisite for the disassembly of the structures, this disassembly is very strongly accelerated in the sterically crowded dendrons and intermediates, where both steric and electronic factors contribute in a synergistic way to the disassembly phenomenon.

Design and Synthesis of BODIPY-Cored Near IR-emitting Lipophilic and Water-Soluble Dendritic Platforms

“…One of the most promising methods for introducing water solubility of BODIPY‐based dyes and related compounds, seems to be the introduction of oligo‐ or polyethyleneglycol appendages ,,,. Accordingly and in the light of abovementioned, we proposed to capitalize on our experience in constructing branched monomers and aryl‐benzyl ether dendrons with functionizable aromatic moiety at the focal point and various terminal functional groups, in particular long aliphatic and oligoethyleneglycol tails . Furthermore, we speculated that the use of such building blocks will add potential conjugation sites to the dye, in addition to altering its solubility properties and absorption/emission profile.…”

Chemoselectivity Improvement via Partial Shielding of an Imidazole Active Site in Branched/Dendritic Homogeneous Catalysts of the Baylis–Hillman Reaction

“…[35][36][37][38][39][40][41] Whereas the assembly of the hydrophobic branchesi sa chieved via the reductiono ft he ester groups of this scaffold, three different synthetic routes were examined for the introduction of the imidazole moiety near the focal point of the future dendron (the phenol hydroxy function). [35][36][37][38][39][40][41] Whereas the assembly of the hydrophobic branchesi sa chieved via the reductiono ft he ester groups of this scaffold, three different synthetic routes were examined for the introduction of the imidazole moiety near the focal point of the future dendron (the phenol hydroxy function).…”

“…We decided to base the synthesis on the 5‐hydroxyisophthalate scaffold, used by us multiple times on previous occasions for the design of dendritic molecules . Whereas the assembly of the hydrophobic branches is achieved via the reduction of the ester groups of this scaffold, three different synthetic routes were examined for the introduction of the imidazole moiety near the focal point of the future dendron (the phenol hydroxy function).…”