Bicyclo[6.1.0]nonyne carboxylic acid (BCN-COOH) is a valuable intermediate for the development of bioorthogonal click reagents. A convenient three-step synthesis of pure diastereomer anti-BCN-COOH is reported here, with an overall yield of 32% starting from 1,5-cyclooctadiene. To the best of our knowledge, this is the shortest route to anti-BCN-COOH known to date. The new method compares favourably with the optimised four-step synthesis based on previously reported data.
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