Rapid Solid-Phase Syntheses of Conjugated Homooligomers and [AB] Alternating Block Cooligomers of Precise Length and Constitution.
A new iterative divergent/convergent solid-phase synthesis of precisely defined oligomers is described. The starting monomer is affixed to the solid support so that both ends are free for growth. The polymer-supported n-mer bearing alpha,omega-terminal iodides is divided into two portions. The smaller portion is converted to the polymer-supported (n + 2)-mer by coupling an alpha,omega-dialkyne to the two iodide ends. The larger portion is liberated from the polymer support and then coupled with the polymer-supported portion to form a polymer-supported (3n + 2)-mer with new alpha,omega-terminal iodide end groups. The process is then repeated. The solid-supported material thereby grows in two directions, unlike the common approach of unidirectional growth. This polymer-supported strategy serves as a pseudo high dilution system so that unwanted polymerization does not ensue. Therefore, after each iteration, the oligomer length is more than tripled, making this a rapid growth methodology for precise oligomer syntheses. The methodology is demonstrated by the synthesis of a 17-mer oligo(1,4-phenylene ethynylene) of approximately 120 Å length in seven steps with an overall 20% yield. This solid-supported divergent/convergent tripling protocol is also used for the synthesis of an [AB] alternating block 23-mer containing oligo(1,4-phenylene ethynylene)s and oligo(2,5-thiophene ethynylene)s in an overall 21% yield. The length of the 23-mer is approximately 160 Å.
Huang
Shenlin
S
Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208 and Rice University, Department of Chemistry and Center for Nanoscale Science and Technology, MS 222, 6100 Main Street, Houston, Texas 77005.
Tour
James M.
JM