Synthesis of an 11-deoxypretetramide derivative

A short and efficient synthesis of the 4-oxo-1,2,3,4-tetrahydro-2-naphthalenecarboxylic acid derivative ($\text{13a}$) is described. This synthon may be converted to the dihydronaphthacenone derivative ($\text{18}$) in a regiocontrolled manner in only two steps using condensation with 2,5-dimethoxybenzaldehyde followed by intramolecular acylation. The enol form of the dihydronaphthacenone, ($\text{20}$) corresponds to a derivative of 11-deoxypretetramide.