Demand for smart and functional materials has raised the importance of the research of dendritic (Greek = tree-like) molecules in organic and polymer chemistry due to their novel physical and mechanical properties.The properties of linear polymers as well as small discrete molecules are combined in this new architectural class of macromolecules, that can be divid- ed into two families: dendrimers and hyperbranched macromolecules, that differ in their branching sequences.Dendrimers contain symmetrically arranged branches emanating from a core molecule together with a well-defined number of end groups corresponding to each generation.This results in an almost monodisperse three-dimensional globular shape provid- ing internal niches capable of encapsulation of guest molecules or molecular recognition. Hyperbranched macromolecules, synthesized in one-step reactions, are randomly branched and contain more defects, i.e. linear and terminal segments, being less homogenic than dendrimers. High chemical reactivity, low viscosity, high solubility and miscibility offer unique tools to modify and tailor properties in particular fields, such as adhesives and coat- ings,agrochemistry,catalysts,chemical and biosensors,cosmetics,inks and toners,lubricants, magnetic resonance imaging agents, membranes, micelle and virus mimicking, molecular recognition, nano devices, pharmaceuticals, self-organizing assemblies, thermoplastics and thermosets, and viscosity modifiers. A short introduction to the first dendritic molecules is accompanied by an illustrated review of dendrimers with polyester functions. In addition future aspects and developments are briefly discussed. Keywords: Dendrimers, Polyester, Supramolecular chemistry, Chirality, Metallodendrimers 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2 Dendrimers with Ester Functions . . . . . . . . . . . . . . . . . . . . 8 2.1 Terminal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.2 Core . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 2.3 Core and Branching . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 2.4 Core and Terminal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 2.5 All Layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 3 Chiral Dendrimers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 3.1 Terminal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 3.2 Core . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 3.3 Branching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 3.4 All Layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 Polyester and Ester Functionalized Dendrimers Sami Nummelin 1 · Mikael Skrifvars 2 · Kari Rissanen 1 1 Department of Chemistry,University of Jyväskylä, PO Box 35, 40351 Jyväskylä, Finland E-mail: Sami.Nummelin@jyu.fi; kari.rissanen@jyu.fi 2 SICOMP, Swedish Institute of Composites, PO Box 271, SE-941 26 Piteå,Sweden Former address: Neste Chemicals Research and Technology, PO Box 310, FIN-06101 Porvoo, Finland Topics in Current Chemistry,Vol. 210 © Springer-Verlag Berlin Heidelberg 2000 4 Metallodendrimers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 4.1 Terminal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 4.2 Branching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 4.3 Core and Branching . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 1 Introduction The concept of highly branched polymers was initially proposed in the early 1940s by Flory [1–4] and Stockmayer [5].Although synthetic efforts failed [6,7], Flory predicted the possibility of such polymers in 1952 by suggesting that it should be possible to polymerize AB x -type monomers (where A is reactive with B and x ≥ 2) to high molecular weight,multibranched products without gelation to an infinite network (Fig. 1) [8, 9]. 2 S. Nummelin et al. Fig. 1. Flory’s randomly branched molecules based on AB 2 monomers [8, 9] Unfortunately, work in this area was not pursued until 1990 when Kim and Webster [10, 11] presented the synthesis of fully aromatic (termed “hyper- branched”) polyphenylenes.Fréchet et al. [12] followed in 1991 with the first one- step synthesis of hyperbranched polyaryl esters based on the thermal selfconden- sation of 3,5-bis(trimethylsiloxy)benzoyl chloride. Since then a wide variety of structures with hyperbranched topology have appeared in the literature including polyamides [13], polyamines [14], polyaramides [15], polyesters [16–27], poly- ester amides [28,29],polyethers [30,31],polyether ketones [32,33],polyphenylene sulfides [34],polysiloxysilanes [35–38],polyurethanes [39–41],liquid-crystalline polymers [42, 43],and metal-containing systems [44, 45]. The first dendrimers, named “cascade” molecules, were introduced by Vögtle et al.[46] in 1978 (Fig.2).“Cascade synthesis”implies that the reaction sequences can be carried out repeatedly, where a functional group is able to react in such way that it appears twice in the subsequent molecule. Since then much of the pioneering work has been credited to the research groups of Denkewalter [47–49], Tomalia [50–53], Newkome [54], Fréchet [55–57], Miller [58–60], Moore [61–64], Meijer [65, 66], and Vögtle [67–69]. Today, dendritic molecules are a topic of interest in over 150 research and devel- opment groups worldwide [70]. The growth in publications has been almost exponential since the late 1980s [71]. More than 2000 publications/patents, over 370 papers in 1997 alone [72, 73], have appeared in the literature including several extensive reviews [74–87]. For this particular reason a comprehensive review that covers all dendritic (i.e. dendrimers and hyperbranched) molecules that contain ester functions is beyond the scope of this article. Thus,the focus is on the progress of dendrimers during the past 5–10 years. The term “dendrimer” originates from the Greek and is a combination of words “dendron” (tree, branch) and “meros” (part). Although a strict definition of the generally used term has not emerged to date, it is widely accepted that dendrimers are highly branched, yet structurally perfect molecules, prepared via iterative synthesis [88]. Further definitions, such as the number of genera- tions, identical constitution of branches, degree of branching (DB = 1), and polydispersity (PDI = 1), should be considered separately in each case. Ulti- mately, each dendrimer is a mixture of similar structures rather than a molecule free of detectable faults. For instance, after 248 consecutive reactions with selectivity of > 99%, the [G-5] ASTRAMOL dendrimer (Fig. 5) possesses a poly- dispersity of 1002, or a dendritic purity of 18% (term introduced by Meijer et al. [89]). Thus, the real amount of dendrimer with 64 terminal amine functions is only 18%, while the rest consists of imperfections with one or more branches missing [90]. The complexity of dendrimers, also known as arborols [54], cascade mole- cules [46], cascadols [91], cauliflower polymers [92], crowned arborols [93], dendrophanes [94], molecular fractals [95], polycules [96], silvanols [97], and “starburst dendrimers”[50],creates problems in naming.Reliance on the IUPAC nomenclature would produce extremely long names that are almost impossible to interpret. Therefore efforts aimed at a more simple nomenclature have been proposed by Mendenhall et al. [95] and Newkome et al. [98–100]. Polyester and Ester Functionalized Dendrimers 3 Fig. 2. Synthesis of “cascade molecules”by Vögtle et al. [46] Dendrimers are constructed in a stepwise manner in repeatable synthetic steps [88]. Each repetition cycle creates an additional layer of branches, called “genera- tion” (or “tier”). Branching multiplicity is dependent on the building block valency, although it can be generated during the growth step from a nonbranched building block as well [50, 65]. In a four-valent core the number of functional groups at the periphery follows the rate 4,8,16,32,when AB 2 -type chain extenders are employed,or the rate 4,12,36,108 for AB 3 -type chain extenders,providing that the branching is perfect. Defects result in branch errors. Errors that occur in the early stage of growth are generally more problematic than those occurring at higher generations,since defects in the dendrimer structure accumulate with each iteration. The problem is not the individual steps in a synthesis as much as the number of successful reactions needed to be done on the same molecule.In addi- tion, each synthesis is only specific to one particular dendrimer. Two major synthetic approaches have emerged: the divergent approach where growth starts from the inside (core) proceeding outwards (Fig.3),and the convergent approach proceeding “outside-in” (Fig. 4), i.e. by first producing “dendrons” (= branches or “wedges”) which are coupled to the core (number of coupling reactions is constant throughout the synthesis). Both methods require two steps for the growth of each generation: the activation of the dendritic unit and the addition of a new monomer. Comparison of these methods show that generally dendrimers prepared by the divergent approach are more polydis- perse than those prepared by the convergent approach [101].Nevertheless, both the commercially available dendrimers (Fig. 5) are prepared by this method. Incomplete reaction arises at higher generations when large number of reactions have to occur on a sterically hindered dendrimer surface. On the contrary, the 4 S. Nummelin et al. Fig. 3. Dendritic growth via divergent approach with AB 2 -type chain extenders. Protection/ deprotection steps (B Æ X) are not necessary if selective chemistry can be adapted. Dots represent the bonds formed between A and X groups [75] convergent method is usually limited to dendrimers of lower generations and yields due to the steric hindrance at the focal points of large dendrons [102].The limits of both methods have yet to be firmly established, but critical molecular design parameters (CMDPs) of size, shape, topology, flexibility, and surface chemistry will eventually set the limits on dendritic growth (dense-packed generation) [84, 86, 92]. One limitation of dendrimers is their time-consuming synthesis.Great effort has been devoted to improving the methodologies for the accelerated construc- tion of dendrimers in response to the need for shorter syntheses. The mixed reactivity approach [103] differs from the divergent method only in that it exploits an additional chain extender, i.e. CD 2 -type, where C can only react with B,and D cannot react with B or C.In double-stage convergent growth [104–106] monodendrons containing a single reactive group at the focal point are coupled in a divergent manner to the periphery of another monodendron or dendrimer. Both double exponential growth [107, 108] and the branched-monomer approach [109,110] are based on an idea where AB x -type chain extenders (x ≥ 4) are employed reducing the number of reaction and purification steps required to reach higher generations.Accelerated dendrimer synthesis [111], also known as the orthogonal coupling method [112–114], halves the reaction steps by obviating (de)protection or activation steps by alternative use of two different building blocks in two complementary coupling reactions. Recently, papers where the divergent and convergent methods are combined have been published [115–117]. This method clearly demonstrates that functionalized dendrimers and dendrons can be employed as reagents in the synthesis of novel compounds. Thus,Vögtle et al. [118] have introduced new technical terms, suggesting the use of “{n}dendryl” for dendritic substituents of n generations and “dendreagent” referring to dendritic reagents. Solid-phase synthesis [119–122], analogous to Polyester and Ester Functionalized Dendrimers 5 Fig. 4. Dendritic growth via convergent approach. Dots represent the bonds formed between two reactive groups Y and X [55, 56] 6 S. Nummelin et al. PAMAM ASTRAMOL Fig. 5. The two commercially available dendrimer families [211] the Merrifield-type peptide synthesis [123], offers advantages such as the use of large excess of reagents without any tedious purification or the use of differen- tially protected core molecules allowing the functionalization of a dendrimer. Bifunctionalized dendrimers can be prepared for instance by employing two differentially functionalized dendrons coupled to the core [124, 125] or via modification of functional groups within the main dendrimer [126–129]. Examples of multifunctionalized dendrimers [130–132] have also been report- ed, such as a combinatorial approach [133] that offers a tool to adjust dendritic properties via modification of the terminal groups. This strategy leads to dendritic materials which possess a variety of forms and terminal functions via simultaneous exploitation of mutually compatible chain extenders at different ratios. The most recent advances in dendrimer construction is the synthesis of cored dendrimers [134] and cyclotrimerization of dendrons attached to the acetylenic moiety in a [2 + 2 + 2] cycloaddition process [135, 136] affording a route to fully substituted benzene-core dendrimers [137]. Dendritic fragments (A) have been linked together with well-known linear polymers (B) as hybrid-linear polymers. End-capping linear polymers, func- tionalized at one or both ends,with reactive dendrons leads to either AB or ABA block copolymers [138–144].Approaches where a dendritic block is grown by a divergent method from suitably modified linear polymers [145–148],or the use of dendrons as macroinitiators for “living” radical polymerizations [149–151] leading to AB copolymers,have emerged.Recently,“dendronized”polymers (i.e. linear polymers bearing dendritic side groups) have received attention [152, 153]. With rigid rod-like backbones these macromolecules resemble a cylindri- cal rather than a globular shape [154–160]. Arborescent graft polymers (“den- drigrafts”) [161–166], including the comb-burst dendrimers [167, 168], are structural analogs of dendrimers. This “graft-on-graft” technique leads to soluble molecules with particularly high molecular weights. Molecular recognition and self-assembly are important topics in supramole- cular chemistry [169–173]. Structural control in the case of dendrimers makes them ideal building blocks for the assembly of larger structures from smaller subunits. Self-assembling dendrimers [174, 175] can be constructed by utilizing non-directional forces (dendritic amphiles) [176], self-organization in liquid- crystalline phases [177–181], p -stacking and intermolecular hydrogen-bonding interactions [182, 183]. Coupling of dendritic units through metal centers has been demonstrated by employing conventional synthetic strategies (i.e. divergent and convergent approaches) [184–189]. Recently, a method where covalent metallodendrimers were synthesized in a one-step reaction by exploit- ing the self-assembly of branching units, followed by in situ substitution of a ligand on the coordination centers,has emerged [190–194].Structurally, metallo- dendrimers can be classified into four categories by the location of the metal complex(es): (1) metal complex as a core, (2) metal complexes in the branches only, (3) metal complexes on the periphery only, and (4) metals as branching centers (all layers) [195]. Use of dendritic fragments has also extended into other fields of supramolecu- lar chemistry. First-generation dendritic rotaxanes [196] and rotaxanes bearing dendritic stoppers have been introduced [197, 198], as well as metalloporphyrin Polyester and Ester Functionalized Dendrimers 7 dendrimers [199–202], C 60 fullerene- [203–207] and calix[4]arene-core dendri- mers [208–210]. Currently, ASTRAMOL and PAMAM dendrimers [211] are being produced on a commercial scale in different generations [212]. These families are widely investigated due to their availability and they are among the most monodisperse non-biopolymers ever produced [66]. In addition, BASF AG (Germany) is pro- ducing poly(propyleneimine) dendrimers on a technical scale [213,214] similar to ASTRAMOL for research purposes. 2 Dendrimers with Ester Functions Dendrimers with ester functions are in focus due to easy access, facile branch- ing, versatility [215, 216], solubility [217], processibility [218, 219], and applica- bility [220–225] of inexpensive raw materials. This technology is actively being developed by Neste Chemicals (Finland) [220, 221] and Perstorp Specialty Chemicals (Sweden) [222–225], for instance, in radiation-curable resin, lubri- cants, binders, and thermoset applications. The first polyester dendrimers are expected on the market by late 2001 from Perstorp under the trade name Boltorn [226, 227]. Related hyperbranched polyesters [228–234] are already being produced on a pilot scale. The following discussion is organized based on the functionality present in the target structure adapting the classification of chiral dendrimers of Peerlings and Meijer [235]. 2.1 Terminal Starburst polyamidoamine (PAMAM) dendrimers [50], introduced by Tomalia et al. in 1985, were synthesized via divergent growth. Branching in the ammonia or ethylenediamine core was obtained via exhaustive Michael addition of methyl acrylate (1) to give the ester 2 followed by amidation with a large excess (15–250 eq.) of ethylenediamine in MeOH (Fig. 6). Higher generations (up to 10) were obtained by repetition of these two reactions.The yields reported were between 98 and 100%.IR, 1 H-, 13 C- and 15 N-NMR,mass spectrometry (MS),size- exclusion chromatography (SEC), gas chromatography (GC), low-angle laser light scattering (LALLS), and electron microscopy were used for the character- ization of the products. Recently, Bradley et al. [121] have demonstrated the solid-phase synthesis of PAMAM dendrimers up to [G-4] by employing a two-directional acid-labile TentaGel resin-bound linker [236], which was easily cleaved by trifluoroacetic acid. Synthesis of arborols [237] by Newkome et al. in 1985 employed a divergent approach with maximized AB 3 -branching for a C-based system.The initial core, 1,1,1-tris(hydroxymethyl) pentane (3), was treated with chloroacetic acid in the presence of t-BuOK/t-BuOH followed by reaction of the intermediate triacid 8 S. Nummelin et al. with methanol to afford 4 (Fig. 7).Reduction of 4 with LiAlH 4 gave the extended triol which was tosylated to yield tritosylate 5. Treatment of 5 with NaC(CO 2 Et) 3 gave nonaester 6. Construction of the [G-3]-dendrimer was accomplished by amide formation. Treatment of 6 with H 2 NC(CH 2 OH) 3 gave the water-soluble [27]-arborol 7 (M w 1626 amu). Products were characterized by 13 C-NMR. “Dumbbell” shaped dendrimers, where two spherical groups are linked through alkyl 8 [238, 239] or alkyne 9 chains (Fig. 8) [240], were obtained by employing similar chemistry. Compounds were shown to form rod-like struc- tures constructed by helical or scissor-like stacking. This property is reflected in the macroscopic tendency to form thermally reversible aqueous gels. How- ever, structures with biphenyl 10 or spirane 11 cores [241] failed to aggregate in aqueous environment. Using the same procedure branches were grown around a benzene core [242]. Mesitylene was brominated with NBS in CCl 4 to give 1,3,5-tris(bromomethyl) benzene followed by treatment with NaC(CO 2 Et) 3 in benzene/DMF to afford the nonaester 12. The [G-2]-dendrimer was prepared by treatment of 12 with tris(hydroxymethyl)aminomethane in DMSO affording the benzene [9] 3 -arborol 13 (M w 1485 amu). The highly water-soluble arborol was converted to benzoate derivative 14 for complete characterization by treatment with benzoyl chloride. All arborols were characterized by NMR and transmission electron microscopy (TEM). Synthesis of silvanols [97] relies on the same synthetic procedure [242]. The crystalline dodecaester 15 a (Fig. 9) was obtained from the initial polytrimethyl- ammonium [1 4 ] metacyclophane [243, 244]. In order to verify that the triester moieties were located on the upper rim, an X-ray structure of dodecaester 15a was conducted. The [G-2] was constructed by treating the resulting ester with H 2 NC(CH 2 OH) 3 in the presence of anhydrous K 2 CO 3 in dry DMSO to afford Polyester and Ester Functionalized Dendrimers 9 Fig. 6. Synthesis of PAMAM dendrimers with an ammonia core [50] [36]-silvanol 16 a. Similarly [72]-silvanol 16b was obtained from the [1 8 ] meta- cyclophane.The transmission electron micrograph of 16a showed small spheres and discrete aggregates with a diameter of ~27 Å for a single molecule. All samples were characterized by IR, NMR, and elemental analysis. Adamantane-core dendrimers [245] were synthesized by treatment of 1,3,5,7-tetrakis(chlorocarbonyl)adamantane (17) with 4-amino-4-(3-acetoxy- propyl)-1,7-diacetoxyheptane (18) [246] in the presence of Et 3 N in benzene solution (Fig. 10). Dodecaacetate 19 was converted quantitatively to the alcohol 20 by transesterification in absolute ethanol. In order to synthesize the dodeca- acid a different synthetic route was developed by using di-tert-butyl 4-amino-2- [(tert-butoxycarbonyl)ethyl]heptanedioate (21) [247]. Treatment of 17 with 10 S. Nummelin et al. Fig. 7. Construction of [27]-arborol using the divergent approach [237] [...]... (10 7) to monomer 10 5 gave the [G -1] -dendron 10 8 (Fig 24) The [G-2]-dendron 10 9 was constructed via Sonogashira reaction of monomer 10 6 and 10 8 Repetition of both reactions led to the [G-4]-dendron 11 1 in four steps By employing the branched monomer approach to increase the efficiency of the synthesis, two new monomers (11 2 and 11 3) were prepared (Fig 25) With these new monomers the [G-6]-dendron 11 8... and shorter reaction times than 1, 1 ,1- tris(4-hydroxy phenyl)ethane The resulting [G-3] 46 (Mw 5644 amu) and [G-4] 47 (Mw 11 ,346 amu) dendrimers (Fig 14 ) were obtained in ~ 90% yields The terminal ethyl ester groups of 46 and 47 were further Fig 14 Surface modification of isophthalate ester terminated polyether dendrimers [252] Polyester and Ester Functionalized Dendrimers 17 modified by hydrolysis, transesterification,... [2 71] have introduced dendrimers containing thermodynamically stable redox-active tetrathiafulvalene (TTF) units at the periphery using convergent growth Reaction of 4-(hydroxymethyl)tetrathiafulvalene (11 9) with 5-(tert-butyldimethylsiloxy)isophthaloyl chloride (12 0) gave compound 12 1 which was deprotected to afford the dendron 12 2 (Fig 26) Coupling of 12 2 with benzene -1, 3,5-tricarbonyl chloride (12 3)... fashion The final dendrimers, up to [G-4], were obtained by coupling of acid chloride dendrons to the 1, 1 ,1- tris(hydroxyphenyl)ethane core 15 4 Characterization was performed by 1H- and 13 C-NMR, SEC, elemental analysis, and pulsed field-gradient spin echo (PGSE) 1H-NMR The effective radii of the dendrimers were estimated from the diffusion coefficients by assuming a spherical geometry for all dendrimers Fig... 34) in five steps with a protecting methyl group as the focal point Monomer 15 6 was reacted with benzoic acid (15 7) to give [G-2]-CO2Me dendron 15 8 which was deprotected as 15 9 and further reacted with 15 6 to give [G-4]-CO2Me 16 0 The methyl-protected [G-3] building block 16 1 was obtained by reaction of 15 6 with [G -1] -CO2H 16 2 Removal of the protecting methyl group by refluxing with ... dendrimers 12 8 (Fig 27) that contain both p-donor (TTF) and p-acceptor (AQ) groups These dendrimers show reversible switching between 27 Fig 24 Orthogonal coupling strategy [11 2] Polyester and Ester Functionalized Dendrimers Fig 25 Orthogonal coupling strategy with a branched monomer approach [11 2] 28 S Nummelin et al Polyester and Ester Functionalized Dendrimers 29 Fig 26 Redox-active polyester dendrimers. .. units [2 71] cationic and anionic states under electrochemical control The sparingly soluble (AQ)2 dendron 13 2 was prepared by the reaction of 2-(hydroxymethyl)anthraquinone (12 9) with silyl-protected isophthalic acid 13 0 followed by deprotection with HCl/THF (7 :1) The (TTF)4 dendron 13 5 was obtained from the reaction of phenol derivative 13 3 (2 .1 eq.) with benzene -1, 3,5-tricarbonyl chloride (12 3) The... suitable a,b-unsaturated carbonyl compounds 13 0af to 1, 3-diaminopropan-2-ol (12 9) under an atmosphere of nitrogen The resulting dendrons were coupled to the core 12 3 in THF using Et3N as catalyst All dendrimers 13 2a–f were fully characterized by 1H- and 13 C-NMR, IR, FAB-MS and SEC 2.5 All Layers Miller et al [275–277] have prepared a series of monodisperse dendrimers based on the convergent synthesis... blocks (Fig 32) Reaction of 13 5a (2 .1 eq.) with 13 6 followed by deprotection (Zn/AcOH) gave the ether-[G-3]-CO2H 14 2 The ester blocks were constructed via coupling of 14 2 with 13 6 Deprotection of the tri- 32 S Nummelin et al Fig 28 Synthesis of moderately sized dendrimers by Twyman et al [274] chloroethyl ester at the focal point afforded [G-4]-CO2H 14 4 which was coupled with 14 0 under standard conditions... Two-directional aromatic polyesters of Haddleton et al [265] 26 S Nummelin et al 10 1 10 2 by catalytic hydrogenation (Pd-C/H2) afforded hydroxy-terminated polyesters 10 3 10 4 Products were characterized by 1H- and 13 C-NMR, IR, GPC with polystyrene narrow molecular weight standards, and MALDI-TOF GPC results for all purified [G-4] -dendrimers indicated the presence of ~ 5% of higher oligomers An interesting . rather than a globular shape [15 4 16 0]. Arborescent graft polymers (“den- drigrafts”) [16 1 16 6], including the comb-burst dendrimers [16 7, 16 8], are structural analogs of dendrimers. This “graft-on-graft”. published [11 5 11 7]. This method clearly demonstrates that functionalized dendrimers and dendrons can be employed as reagents in the synthesis of novel compounds. Thus,Vögtle et al. [11 8] have. required to reach higher generations.Accelerated dendrimer synthesis [11 1], also known as the orthogonal coupling method [11 2 11 4], halves the reaction steps by obviating (de)protection or activation