Why is adding the MeO necessary?

(H2,MeCHOAcClMeOH= i) Ac2O,AeCH, eat H2SO4 D-ribose guane. a/b \begin{tabular}{|c|} \hline Furanose forna sownth \\ Intescoaverts ala \\ mutarotation \\ \hline \end{tabular} Furanose form OSI.Y AcO. Mislure of anothen i) NaChe