Abstract
An efficient flow process for the selective hydroboration and oxidation of different alkenes using 9‐borabicyclo(3.3.1)nonane (9‐BBN) allows facile conversion in high productivity (1.4 g h−1) of amorpha‐4,11‐diene to the corresponding alcohol, which is an advanced intermediate in the synthesis of the antimalarial drug artemisinin. The in situ reaction of borane and 1,5‐cyclooctadiene using a simple flow generator proved to be a cost efficient solution for the generation of 9‐BBN.
Highlights
Shown in Scheme 2 is a key step in the synthesis of the antimalarial drug artemisinin 6, which can be achieved in batch using 9-borabicyclo(3.3.1)nonane (9-BBN).[5]
Oxidation of alkenes to the corresponding alcohols is one of the fundamental chemical transformations and the hydroboration– oxidation sequence is an important tool in this context.[2]
Initial investigations were based on the optimised reaction conditions for the sequence of hydroboration and oxidation of alkenes in flow as published by Souto et al.[3]
Summary
Shown in Scheme 2 is a key step in the synthesis of the antimalarial drug artemisinin 6, which can be achieved in batch using 9-borabicyclo(3.3.1)nonane (9-BBN).[5]. The selective oxidation of the terminal double bond of amorpha-4,11-diene 4 to the corresponding alcohol 5 as Initial investigations were based on the optimised reaction conditions for the sequence of hydroboration and oxidation of alkenes in flow as published by Souto et al.[3] Using a modified reaction setup (Figure 1) and replacing borane by 9-BBN, the selective oxidation of the terminal alkene of (R)-(+)-limonene was investigated as a cheap and accessible model substrate.
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