Complex sentence: Meldrum's acid has a high acidity with a pKa of 4.97, because, like ascorbic acid, deprotonation at the methylene "next to" the carbonyls produces a stable enolate.
Split into simpler sentences: Meldrum's acid has a high acidity with a pKa of 4.97. Like ascorbic acid, deprotonation at the methylene next to the carbonyls produces a stable enolate.