Well-defined oligo(pyrrole-2,5-diyl)s by the Ullmann reaction

The Ullmann coupling reaction has been used to polymerize N-t-BOC-2,5-dibromopyrrole into well-defined oligo(pyrrole-2,5-diyl)s. After optimization of the reaction conditions, i.e. using 1 wt equiv of Cu-bronze in DMF at 100 "C for 1 h, oligomers up to 25 repeating pyrrole units are obtained. Starting from 5,5‘- and 5,5"-dibrominated N-t-BOC protected bi- and terpyrrole as monomers, the polymerization is slower and a lower degree of polymerization is observed, yielding oligomers with an even lower molecular weight than those resulting from N-t-BOC-2,5-dibromopyrrole. The first 20 oligomers of poly(N-t-BOC-pyrrole)h ave been isolated by preparative HPLC. Characterization of the individual oligomers shows that they all are hydrogen terminated and possess a perfect 2,5-linkage: oligo(pyrro1e-2,5-diyl)s. The isolated oligomers have been used to study the optical and electrical properties of the oligomers as a function of chain length

A mild and convenient method for the preparation of multi-isocyanates starting from primary amines

A mild and convenient method for the synthesis and isolation of multi-isocyanates, obtained from the reaction of the corresponding primary amines with di-t-butyltricarbonate (1) is described

Chirality in Dendritic Architectures

A review with 38 refs. At first glance the topic of chiral dendrimers seems to be a contradiction in terms. However, recent studies reveal that both the building blocks of the dendrimer and the overall dendritic architecture can be chiral and that chirality can be introduced at various levels. The expression of optical activity in these enantiomerically pure dendrimers as a result of conformational (dis)order has proven to be of special interest. We present the different approaches to introducing chirality in dendritic architectures, organized through their possible impact in fields such as biocompatibility, catalysis, mol. recognition, and surface chem. Also, the relation between mol. chirality of core or building block and the macroscopic chirality of dendritic objects is discusse

Synthesis and Characterization of axially chiral molecules containing dendritic substituents

Enantiomerically pure, axially chiral (S)-1,1'-bi-2-naphthol was used as a core material to which Frechet-type dendritic wedges of the 0th up to the 4th generation were attached, yielding the axially chiral dendrimers. The chiroptical features of these compds. were studied and revealed an increasing molar optical activity for higher generations of dendrimers. This effect can be explained by a larger torsional angle between the naphthyl units, caused by steric repulsions between the dendritic wedges. However, the effect is marginal, indicating a high degree of flexibility present in the axially chiral dendrimer

Chiral objects with a dendritic architecture

The synthesis and characterization of both enantiomers of 2-(benzyloxy)-1-[3,5-bis[[3,5-bis(benzyloxy)]benzyloxy]benzyloxy]-3-[[3,5-bis(benzyloxy)]benzyloxy]propane (I; S-7 and R-7) are described. The chirality is based on the linkage of three constitutionally different, but chem. similar, dendritic wedges with a chiral glycerol derived core. Both enantiomers are synthesized from the same starting material: S-(+)-Solketal. Despite their enantiomeric purity, S-7 and R-7 lack any optical activity and may be regarded as the first macromol. analogs of the well-known org. mols. with \"accidental degeneracy\" or \"cryptochirality.\

Chiral dendrimers with backfolding wedges

Dendritic wedges with a substitution pattern that forces the growth inwards are introduced and the use of this new building strategy is exemplified in the synthesis and chiroptical properties of a chiral dendrime

Fast and convenient construction of carbamate/urea-based dendrimers by making use of a diisocyanate building block

A novel, fast, and simple synthetic procedure for polycarbamate/urea dendrimers, based on an AB-CD2 coupling strategy, is presented. The reactivity difference of the two isocyanate functionalities of the AB building block allows the construction of these dendrimers without the necessity of activation or deprotection steps. This makes it possible to construct dendrimers within 2-3 days, even the largest dendrimers. The resulting dendrimers could be fully characterized by 13C NMR, IR spectroscopy, and mass spectrometry. The synthetic strategy necessitates only techniques such as stirring, heating, and accurate dosing, and there is no workup required for the purification of the compounds. On account of a wide variety of polyols, amines, and aminoalcohols, this new procedure is not limited to the synthetic strategy followed but allows the incorporation of a large variety of functional molecules in the core, in the branching units, or at the end groups. The method is even applicable when organometallic species are incorporated into the dendritic structure, thereby showing its versatility. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3112-3120, 200