Functionalisation of Chromane by Deprotonative Metallation

Abstract

Despite the biological interest in chromane derivatives, few studies dedicated to the functionalisation of this heterocycle have been reported. Herein, our objective is to demonstrate the potential of alkali metal bases for the introduction of substituents at its positions 4 and 8, and to explain the observed reactivity based on quantum chemical calculations. Guided by these theoretical results, preliminary optimisation was carried out on 2,3‐dihydrobenzofuran before applying the optimal conditions to chromane. Deprotolithiation at C8 was thus achieved using n‐butyllithium in hexane at room temperature, while functionalisation at C4 was promoted by a 1:1 mixture of lithium 2,2,6,6‐tetramethylpiperidide and potassium tert‐butoxide in tetrahydrofuran at ‐50 °C. Various electrophiles were used to intercept the lithiated intermediates, providing a convenient access to substituted chromane derivatives.