I was just looking at a particular synthesis method on the Organic Chemistry Portal when I saw a particularly puzzling step, involving a 1,3-dicarbonyl compound. The step which I am puzzled by is shown here:
The second step, acid-catalysed esterification is unambiguous. It is the first step which opens the ring which concerns me. The fact that esterification occurs in the second step seems to suggest that the product of the acid-catalysed ring opening in the first step is a carboxylic acid and I simply cannot see how it can possibly form. Would someone kindly enlighten me on step 1?