Phenylacetylene oligomers

By using monomers with different substituents, multiple functionalities could be introduced into the phenylacetylene oligomer at any desired position along the sequence backbone, resulting in macrocycles with a wide variety of symmetries (e.g. 47-53). In principle, this versatile synthetic method should allow construction of PAMs in which anyparticular group couldbe placed at any particular site. Judicious choice of the type and placement of functionalities has... 

Nelson, J. C. Young, J. K. Moore, J. S. Solid-Phase Synthesis of Phenylacetylene Oligomers Utilising a Novel 3-Propyl-3-(benzyl-supported) Triazene Linkage, J. Org. Chem. 1996, 61, 8160-8168. 

SOLID-PHASE SYNTHESIS OF SEQUENCE-SPECIFIC PHENYLACETYLENE OLIGOMERS... 

Efficiency of the deprotection and coupling reactions are critical to the success of any iterative solid-phase synthesis. Shown in Scheme 1 is a triad of reactions for phenylacetylene oligomer synthesis trimethylsilyl deprotection,28 29 triazene unmasking of an iodobenzene,30 and the Sonogashira coupling of a terminal acetylene with an aryl iodide.31-33 Representative procedures for each step in this sequence are included at the end of this chapter. 

A comparative study of phenylacetylene oligomer synthesis on a solid support14 with solution-phase approaches has been undertaken.37 Results from syntheses featuring a free and bound terminal acetylene are shown in Scheme 5. (For clarity, substituted arene units are symbolized as a filled circle throughout the rest of this chapter.)... 

Figure 4.7. Infrared spectra used to monitor cross-coupling and deprotection reactions on resin-bound phenylacetylene oligomers. Observation of a null at 3311 and 2156 cm-1 corresponds to complete acetylene coupling and trimethylsilylacetylene deprotection, respectively.

Other laboratories have used FTIR spectroscopy to determine the kinetics of reactions on different polymer supports39 and to enumerate factors regulating site interactions in different types of supports (see Chapter 7, p. 219).40 A major weak point of the procedure is the need for IR diagnostic functions or changes in hybridization to be involved in the transformation to be investigated. For phenylacetylene oligomers, however, the TMS and terminal acetylene absorptions are ideal. 

Moore et al. 100 expanded the use of the complimentary protection-deprotection sequence, facilitated by the diethyltriazine and trimethylsilane groups, to construct phenylacetylene oligomers. Up to 16 arylalkyne units were successfully connected (overall yield 67 % 2251 amu). The method, demonstrating a high level of chain length control ,... 

Scheme 5.31. An iterative procedure for the construction of phenylacetylene oligomers.

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