Dibenzobc,fg1,4oxathiapentalene: an elusive molecule?

摘要

Dibenzobc,fg 1,4dithiapentalene (1) has previously been prepared by an intramolecular nucleophilic aromatic substitution (S_NAr) reaction of 9-fluorodibenzob,dthiophen-1-thiol (X,Y = S). Instead, subjecting 9-fluorodibenzob,dbenzofuran-1-ol (X, Y = O) to similar reaction conditions provided a macrocycle (5), as a result of an intermolecular S_NAr cyclization, rather than dibenzobc,fg1,4dioxapentalene (3). To shed further light on this reaction type, we here present an attempt to prepare the mixed (O.S) compound dibenzobc,fg1,4oxafhiapentalene (7) from 9-fluorodibenzob,dthiophen-1-ol (11, X = S, Y = O). However, like a previous strategy to make this molecule, the attempt failed. We rationalize the results by a computational study of the reaction energetics and profiles of the S_NAr reactions.