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4.7. REPRESENTATIVE PROCEDURES 143
DMF, methylene chloride, and MeOH and then dried in vacuo to a constant mass giving resin-bound oligomer as light yellow to brown polymer beads.
4.7.5. Preparation of Propylaminomethylated Resin
See Scheme 4. A suspension of chloromethyl polystyrene-1% divinyl benzene copolymer beads (66.0 g, 0.700 mequiv Cl, 200-400 mesh) and n-propylamine (300 mL) was degassed and heated at 70°C for 86 h in a sealed tube. The polymer was transferred to a coarse sintered glass filter using methylene chloride and washed with methylene chloride (400 mL). The resin was then thoroughly washed according to the following protocol to remove non-covalently bound material. Resin was placed in a 1-L flask, fitted with a magnetic stirrer at 70°C and stirred slowly with dioxane-2 N NaOH (1:1, v/v, 400 mL) for 30 min. Solvent was removed by aspiration through a coarse sintered glass filter. This was repeated once with dioxane-
2 N NaOH (1:1, v/v, 400 mL), twice with dioxane-water (1:1, v/v, 400 mL), followed by hot DMF (1 L), methanol (1 L), and benzene (1 L). The resin was then rinsed with hot methanol (1 L) and dried in vacuo to a constant mass to give white propylaminomethyl poly(styrene)-l% divinyl-benzene copolymer beads.
4.7.6. Generation of a Diazonium Salt
To a dry three-neck 250-mL round-bottom flask equipped with a 100-mL addition funnel and nitrogen inlet is added boron trifluoride etherate (8.14 mL, 66.2 mmol) (Scheme 12). The flask is then chilled to -15°C in an ice-acetone bath. The aryl amine (4.5 g, 16.54 mmol) is dissolved in THF and added slowly over 20 min. te/t-Butyl nitrite (6.9 mL, 57.9 mmol) in THF is then added to the mixture over 30 min. The reaction is stirred another 10 min at -15°C and then warmed to 5°Ñ over 20 min. Hexane is added (300 mL) to the mixture upon which a solid precipitates. The solid is removed by filtration and washed with cold ether and dried in vacuo to give
144 SOLID-PHASE SYNTHESIS OF SEQUENCE-SPECIFIC PHENYLACETYLENE OLIGOMERS
3-bromo-5-hexyloxybenzenediazonium tetrafluoroborate (5.62 g, 15.22 mmol, 92%) as a yellow powder.
4.7.7. Preparation of Triazene-Tethered Monomer
To a chilled (0°C) suspension of n-propylaminomethyl poly(styrene)-l% divinylbenzene copolymer beads (4.32 g, 0.522 mequiv N/ g resin, 2.25 mmol, 200-400 mesh), finely ground potassium carbonate (590 mg, 4.5 mmol), and DMF (50 mL) was added 3-bromo-5-hexyloxybenzenedia-zonium tetrafluoroborate (1.0 g, 2.69 mmol) in portions over 1 h (Scheme 13). After each addition, an aliquot of the DMF supernatant was diluted in diethylamine and analyzed by GC. Once diethyltriazene was detected, the additions were ceased and the suspension was transferred to a fritted filter using DMF and washed sequentially with 120 mL of the following solvents: MeOH, water, MeOH, THF, and MeOH. The beads were then dried in vacuo to a constant mass to give l-(3-bromo-5-hexyloxyphenyl)-3-propyl-3-(ben-zyl supported) triazene as light yellow material.
This work was supported by the National Science Foundation.
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