Unexpected Dual Acylation of Naphtho[2,1-b]furan at the Aryl and Hetaryl Ring: Experimental and Theoretical Study

Abstract

Depending on the reaction conditions, the acylation of 2-ethylnaphtho[2,1-b]furan leads to the formation of a mixture of 1-acetyl-, 5-acetyl-, and 1,5-diacetyl derivatives with a widely varying ratio of components, the structure of which has been characterized by IR and NMR spectroscopy, mass spectrometry, and X-ray diffraction analysis methods. Quantum-chemical simulations using the DFT B3LYP/6-311++G** method have reproduced the experimental geometry of isomeric acetyl[2,1-b]furans and indicated their close thermodynamic stability. However, the Fukui indices of the reactivity f⁻ have indicated the preference of the primary attack of the electrophile at the C⁵ position (f⁻ = 0.18) as compared to the C¹ position (f⁻ = 0.06).