Oligomer reaction sequence

Figure 1. Reaction sequence for AT arylether sulfone oligomers.

Monomer/Oligomer Synthesis. The first two steps in the four step reaction sequence of Figure 1 are capable of producing both monomer and oligomer. The first step, aromatic nucleophilic substitution, is a polymer forming reaction under the correct stoichiometric conditions. In order to favor the formation of monomer with a small amount of oligomer, the substitution was carried out at a 4 1 ratio of diol to dichlorodiphenyl sulfone. This led to a predominantly monomeric product (IV) with only the requirement that the excess diol be removed from the product to eliminate the potential presence of low molecular weight species in later reactions. 

All of the sulfone diols were able to form oligomers in the second step of the reaction sequence, the Ullmann ether synthesis. As with the synthesis of the mono(bromophenoxy)phenol products, two methods were used to form the dibromo materials. Method A used pyridine, potassium carbonate and cuprous iodide, while Method B employed collidine and cuprous oxide with the dibromobenzene and higher molecular weight diol (IV). The major difference between the syntheses of the mono(bromophenoxy)phenols described earlier and these lies in the stoichiometry of the reactions. In order to... 

The monomer/oligomer mixtures were used In the third step of the reaction sequence, the replacement of bromine with 2-methyl-3-butyn-2-ol by use of the bls(trlphenylphosphlne) palladium chloride catalyst system. This reaction used a trlethylamine/pyridine solvent system to replace the bromines on the ether sulfone with ethynyl groups protected by acetone adducts. The acetone protecting groups were then removed In a toluene/methanol/potasslum hydroxide solvent system. 

Ring-opening metathesis (ROM) oligomers were used as a soluble support for this reaction sequence 38-43 <20030L15> with the yield 50-55% (Scheme 4). 

The absorption lines of the low temperature photoreaction products in TS-6 monomer crystals are summarized in the diagram of Fig. 7. The correlation of the A, B, C,. .. photoproduct series to diradical DR intermediates and of the b, c, d,... photoproducts to asymmetric carbene AC intermediates is based on the ESR experiments discussed below. The correlation of the y, 8,6,... series to stable oligomers SO is based on their thermal and optical stability. The correlation of dimer, trimer, tetramer,... molecules follows from the chemical reaction sequences observed in the time resolved optical and ESR measurements as well as from the widths of the one-dimensional potential wells used in the simple electron gas theory , which already has proved successful in its application to dye molecules. Following Exarhos et al. the explicit dependence is given by... 

Methylthiopurine phosphoramidite 193 has been prepared and incorporated into oligomers. An improved synthesis of the 2 -deoxy-2-fluoroinosine nucleoside has been described. The key step in the reaction sequence is the mild... 

Phase effects in the oligomerization of l-aIIyl-l,2-dicarba-doso-dodecaborane by electron radiolysis have been investigated. Liquid state radiolysis indicates an activation energy of ca. 5 kcal moP for the formation of oligomer, and ca. 0 kcal mol for the formation of unsaturated dimers. For the plastic crystalline phases, negative activation energies were observed, indicating the existence of a complex reaction sequence." ... 

The metal-halogen exchange reaction must be carried out at low temperatures ( — 50°C), and the lithiated polymer can then be allowed to react with ClPPhj, ClSnPhj, ClAuPPhj or CO 2. The triarylphosphine groups then function as coordination sites for a variety of transition-metal systems. It should be noted that complex reaction sequences of this type require prior model compound studies with the analogous cyclic oligomers . 

A solid-phase submonomer approach to A-substituted j8-aminopro-pionic acid oligomers or )8-peptoids has been developed by Hamper et al. [63]. It is based on a simple two-step acylation and Michael addition reaction sequence. Treatment of Wang resin with 2 equiv. of acryloyl chloride in the presence of triethylamine in excess afforded the corresponding acrylate resin 86 (Scheme 23) [63]. Michael addition of a 6- to 10-fold excess of a given primary amine in DMSO afforded polymer-bound A-substituted -alanines (87). Trimeric A-benzyl-j8-aminopropionic acid (88) was prepared in 67% overall yield by repetition of this two-step sequence. 

Subsequently the purines can be synthesized by further reactions with HCN, cyanogen or cyanate. Alternatively, hydrolysis of the oligomer under mild conditions yields adenine as well as a number of other products (Ferris et al., 1977 and 1978 see Table III). The purines guanine, hypoxanthine and xanthine have also been tentatively identified (Ferris et al., 1978 Schwartz and Goverde, unpublished). It is significant that no additional ammonia need be added for this reaction sequence (ammonia is, however, produced during the oligomerization and the hydrolysis). 

The general procedure for separation of monomer from oligomer was column chromatography. Separations were normally carried out after the Ullmann reaction, at the dibromo stage of the reaction sequence. The dibromo aryl-ethers were then converted as monomer or as a combination of monomer and oligomer to the acetylenes. The following are representative of the procedures used ... 

This reaction sequence offers the advantage of being able to prepare linear oligomers under simplified reaction conditions and then couple them with formal linkages to get pol3rmers with properties which are hopefully not too much different from the homopolymers themselves. 

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