In our group Intramolecular Silyl Nitronate Cycloadditions involving triple bonds (ISNC) produces carbonyl oxygen that are believed to come from the isoxazole ring of the silyl nitronate intermediate. Our goal was to examine the role of aqueous work-up in the formation of the dihydrofuran carbonyl products. Ketone and aldehyde products were prepared and tested for incorporation of water during ring opening of the intermediate and/or hydration. Four different ISNC reactions were completed to produce two aldehydes and two ketones. One of each intermediate was quenched with acidic O18-labeled water, while regular water was used for the others. The controls were then tested for hydration with acidic O18-labeled water. The molecular ionization peaks of each product were analyzed for enhancement. When tested against theoretical calculations, the appearance of an M+3 peak, along with enhancement of the M+2 peak, would prove O18 incorporation. Likewise, no M+2 enhancement and the absence of an M+3 peak would prove that the carbonyl oxygen originates in the isoxazole ring of the intermediate. We found that hydration played a significant role in both the aldehyde and ketone products.