Concave Reagents, 45.  2,6-Di-tert-butylpyridine-Loaded Dendrimers and Their Use in Vinyl Triflate Synthesis
02. Mai 2005 (online)
2,6-Di-tert-butyl-pyridine (DTBP) has been connected with dendrons and dendrimers of the Fréchet type. Four dendrimers, both first and second generation derivatives have been synthesized and used as non-nucleophilic, recyclable bases in the formation of cyclohexenyl-1-triflate from cyclohexanone.
steric hindrance - dendrimers - triflate - base catalysis - recycling
- 1 Concave Reagents, 44:
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Besides M+ and M+ + 1, a signal at 2219 [M+ - 325] was detectable but did not match any fragments. Relative intensities did not change upon variation of the laser power. Possibly, impure dendrons have been used lacking one pyridine and one dihydroxybenzyl alcohol unit. In other batches using dendrons which had been purified by GPC, this impurity could be avoided.16
As for 14, [M+ - 325] signals could be detected (m/z = 3519), probably because the dendron contained the same impurity. Again, the impurity could be avoided when dendron 13 was purified by GPC.18
Sometimes the material had to be purified by GPC which lowered the yield.