(a) (b) (c) (d) Br Dihydropyran can be used as a protecting group for alcohols: *O*...

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(a) (b) (c) (d) Br Dihydropyran can be used as a protecting group for alcohols: *O* dihydropyran he catalytic H H* dihydropyran H₂O On the previous page, draw the missing intermediate products in the boxes provided. Why is a protecting group necessary for this reaction sequence to work? [2 marks] Grignard reagents cannot be formed in the presence of acidic protons (such as the OH in an alcohol). In order to form the Grignard reagent, the alcohol must first be protected so that it doesn't have any acidic protons. *O* dihydropyran Propose a reasonable mechanism for the reaction between 1-bromoethanol and dihydropyran. You may use HA as shorthand for the catalytic acid and A as shorthand for its conjugate base. [3 marks] Mg THF :N=C—CH3 catalytic Hi WI....Cerence to your mechanism in part (c), explain the regiochemistry observed in the reaction between an alcohol and dihydropyran. In other words, why does the reaction below NOT occur? [3 marks] catalytic H O (a) (b) (c) (d) Br Dihydropyran can be used as a protecting group for alcohols: *O* dihydropyran he catalytic H H* dihydropyran H₂O On the previous page, draw the missing intermediate products in the boxes provided. Why is a protecting group necessary for this reaction sequence to work? [2 marks] Grignard reagents cannot be formed in the presence of acidic protons (such as the OH in an alcohol). In order to form the Grignard reagent, the alcohol must first be protected so that it doesn't have any acidic protons. *O* dihydropyran Propose a reasonable mechanism for the reaction between 1-bromoethanol and dihydropyran. You may use HA as shorthand for the catalytic acid and A as shorthand for its conjugate base. [3 marks] Mg THF :N=C—CH3 catalytic Hi WI....Cerence to your mechanism in part (c), explain the regiochemistry observed in the reaction between an alcohol and dihydropyran. In other words, why does the reaction below NOT occur? [3 marks] catalytic H O

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