Past exam of the chemistry B course of the University of Cambridge / 2025 / Paper 1 / B1 / a / ii

The product is N-[5-(2-chloroacetyl)-2,3-dihydrobenzofuran-6-yl]acetamide, with an aromatic $-\mathrm{COC}{\mathrm{H}}_2\mathrm{Cl}$ substituent at position 5. Substitution of one aromatic hydrogen by ${\mathrm{C}}_2{\mathrm{H}}_2\mathrm{ClO}$ gives the stated molecular formula. This positional assignment also agrees with the isolated intermediate reported in the original process study.^[ref]

GaCl3 activates chloroacetyl chloride by Lewis-acid coordination and chloride abstraction, represented by the acylium/contact-ion-pair limit $\mathrm{ClC}{\mathrm{H}}_2\mathrm{C}{\mathrm{O}}^{+}$. The position-5 aromatic $\pi$ bond attacks the acyl carbon, giving a Wheland intermediate. Removal of the proton at that carbon restores aromaticity. Product–Lewis-acid coordination is reversed on work-up. The carbon-bound chlorine survives; the chlorine on the acyl carbon is the leaving group.