Continuous Flow β-Zeolite Catalysed Regioselective Alkylation of Naphthols Using Alcohols for Synthesis of Peroxynaphthalen-2(1H)-one, Azidonaphthalen-2(1H)-one and Fluoronaphthalen-2(1H)-one Derivatives

Abstract

Functionalized naphthols are prominent scaffolds in organic synthesis and materials chemistry. Herein, we demonstrated continuous flow alkylation of α- and β-naphthols by using various primary and secondary benzylic alcohols in the presence of environmentally benign granular β-zeolite as a reusable catalyst. For a variety of β-naphthols, the respective alkylated products with good regioselectivity were obtained in high yields under mild reaction conditions. This protocol proceeded via the classical Friedel-Crafts type alkylation process and generated stable carbocations as intermediates. Applying this protocol, versatile naphthol derivatives have been synthesized using primary and secondary benzylic alcohols (50 and 44 examples in batch and continuous flow process, respectively), with good yields. Key advantages of this process includes rapid and efficient transformation, facilitates gram-scale synthesis, and generates water as the sole by-product. The most significant advantage is the continuous reusability of granular β-zeolite, which further emphasizes the sustainability of the method. The application of alkylated naphthols for quaternary functionalization was demonstrated through peroxidation, azidation, and halogenation reactions under the continuous flow module, which yielded the respective peroxynaphthalen-2(1H)-one, azidonaphthalen-2(1H)-one and fluoronaphthalen2(1H)-one derivatives.