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Despite further attempted optimization, the highest yield of
839–864.
phosphoramidite 9 obtained was a modest 17%. The oxidised phos-
phoramidate was still the major product, obtained in 79% yield.
Nonetheless, this represents the first synthesis of such a symmet-
rically disubstituted bis-nitrogen-heterocycle containing phospho-
ramidite. Furthermore, phosphoramidite 9 was only moderately
air-stable, undergoing ca 10% oxidation when left to stand in air
for one hour.
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3. Conclusion
We have successfully synthesised the first example of a 3,30-bis-
N-heterocycle containing BINOL-based phosphoramidite. The tria-
zole forming azide-alkyne cycloaddition proceeded only in the
presence of a Cu(I) salt in acetonitrile. Such functionalised phos-
phoramidites are prone to oxidation at phosphorus to give the
corresponding phosphoramidates. The nature of the pendant
heterocycle has an influence on the rate of this oxidation – with
pyridine compounds being more rapidly oxidised than the corre-
sponding triazole containing compounds. Given this shortcoming,
the search for a robust N-heterocycle containing phosphoramidite
is ongoing.
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References and notes
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