Stitching reaction

Other novel polymethylene architectures can be obtained by related stitching reactions of polyhomologated organoboranes produced from structurally novel initiators. For example, the... 

Scheme 11.10 An illustration of the synthesis of macrocyclic polymethylene 28 from a side-chain-blocked boracyclane initiator 26 followed by two-arm stitching reaction.

Although beyond the scope of the present discussion, another key realization that has shaped the definition of click chemistry in recent years was that while olefins, through their selective oxidative functionalization, provide convenient access to reactive modules, the assembly of these energetic blocks into the final structures is best achieved through cydoaddition reactions involving carbon-het-eroatom bond formation, such as [l,3]-dipolar cydoadditions and hetero-Diels-Al-der reactions. The copper(i)-catalyzed cydoaddition of azides and terminal alkynes [5] is arguably the most powerful and reliable way to date to stitch a broad variety... 

The Ghadiri group used metathesis to "fix a system formed by self-assembly. In this cyclic peptide system, the dimer is formed by complimentary hydrogen bonds [33], after which the metathesis reaction "stitches the two halves together to form a stable structure (Eq. 6.12). 

DNA polymerases work by stitching together two nucleotides, one at the 3 end of a DNA chain and the other a deoxynucleic acid triphosphate. The two are held in position near each other by hydrogen bonding to the template DNA chain and are joined by reaction of the first phosphate of the triphosphate with the OH of the saccharide ring of the other base, releasing diphosphate. Mg ions separated by about 390 pm are bound on each side of the phosphorus in the transition state, as in Figure 16-23. 

Lee and Char [93] studied the reinforcement of the interface between an amorphous polyamide (PA) and polystyrene with the addition of thin layers of a random copolymer of styrene-maleic anhydride (with 8% MA) sandwiched at the interface. After annealing above the Tg of PS, they found significantly higher values of Qc for samples prepared with thinner layers of SMA than for the thicker ones. They initially rationalized their results by invoking the competition between the reaction rate at the interface and the diffusion rate of the SMA away from the interface. For very thick layers, and therefore also for pure SMA, the reaction rate was much faster than the diffusion rate away from the interface and favored therefore a multiple stitching architecture, as shown schematically in Fig. 50. Such an interfacial molecular structure does not favor good entanglements with the homopolymer and is mechanically weak. 

Cyclopentenones. The carbonylative stitching method for cyclopentenone synthesis, typified by the Pauson-Khand reaction, includes the variant of using Fe(CO)s under carbon monoxide at relatively high temperatures. 

C.D. Cantrell, S.M. Freund, J.L. Lyman, Laser induced chemical reactions and isotope separation, in Laser Handbook, vol. 3, ed. by M.L. Stitch (North-HoUand, Amsterdam, 1979) R.N. Zare, Laser separation of isotopes. Sci. Am. 236, 86 (1977) ... 

The third class of olefin methathesis in Scheme 21.1 is addition metathesis polymerization (ADMET). This reaction is an alternative method to stitch together olefins into polymers, in this case by a combination of dienes with extrusion of ethylene. Control of molecular weight by the ADMET process is less precise than that by ROMP, but this reaction has been used to make polymers with precise architectures, such as polymers that would be perfectly alternating ethylene-propylene copolymers. ... 

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