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Catalytic Chan – Lam coupling using a ‘ tube-in-tube ’ reactor to deliver molecular oxygen as an oxidant

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ABSTRACT

A flow system to perform Chan–Lam coupling reactions of various amines and arylboronic acids has been realised employing molecular oxygen as an oxidant for the re-oxidation of the copper catalyst enabling a catalytic process. A tube-in-tube gas reactor has been used to simplify the delivery of the oxygen accelerating the optimisation phase and allowing easy access to elevated pressures. A small exemplification library of heteroaromatic products has been prepared and the process has been shown to be robust over extended reaction times.

No MeSH data available.


Syntheses of substrate 39.
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C3: Syntheses of substrate 39.

Mentions: Using N-heterocyclic substrates as the nucleophilic partner with a range of different phenylboronic acids generally gave good isolated yields (19, 20, 28–35, Scheme 2). Using a pyradizine as a nucleophilic partner an 81% yield was obtained for the formation of 20. However, using 3,4-dimethyl-1H-1,2,4-triazol-5(4H)-one (39), which was synthesised using a literature procedure [17–18] (Scheme 3), with 3,4-dimethoxyphenylboronic acid gave a lower yield of 26% (28, Scheme 2). It is not yet clear as to why such a low conversion and isolated yield was obtained although the reduced nucleophilicity and higher potential for coordination of the triazole to the copper catalyst might inhibit catalyst turnover and account for this.


Catalytic Chan – Lam coupling using a ‘ tube-in-tube ’ reactor to deliver molecular oxygen as an oxidant
Syntheses of substrate 39.
© Copyright Policy - Beilstein
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4979635&req=5

C3: Syntheses of substrate 39.
Mentions: Using N-heterocyclic substrates as the nucleophilic partner with a range of different phenylboronic acids generally gave good isolated yields (19, 20, 28–35, Scheme 2). Using a pyradizine as a nucleophilic partner an 81% yield was obtained for the formation of 20. However, using 3,4-dimethyl-1H-1,2,4-triazol-5(4H)-one (39), which was synthesised using a literature procedure [17–18] (Scheme 3), with 3,4-dimethoxyphenylboronic acid gave a lower yield of 26% (28, Scheme 2). It is not yet clear as to why such a low conversion and isolated yield was obtained although the reduced nucleophilicity and higher potential for coordination of the triazole to the copper catalyst might inhibit catalyst turnover and account for this.

View Article: PubMed Central - HTML - PubMed

ABSTRACT

A flow system to perform Chan–Lam coupling reactions of various amines and arylboronic acids has been realised employing molecular oxygen as an oxidant for the re-oxidation of the copper catalyst enabling a catalytic process. A tube-in-tube gas reactor has been used to simplify the delivery of the oxygen accelerating the optimisation phase and allowing easy access to elevated pressures. A small exemplification library of heteroaromatic products has been prepared and the process has been shown to be robust over extended reaction times.

No MeSH data available.