Identify the major product formed in the following reaction sequence: Step 1: + TsCl (2 equiv.) / pyridine Step 2: Product of Step 1 + Step 3: Aq. NaOH Step 4: H ⁺ /

Step-by-step solution

Step 1: The starting material is a derivative of D-threitol, where the two methoxy (-OMe) groups are on opposite sides in the Fischer projection. Reaction with 2 equivalents of tosyl chloride (TsCl) in pyridine selectively tosylates the two primary alcohols, forming 1,4-di-O-tosyl-2,3-di-O-methyl-D-threitol. Step 2: Ethyl acetoacetate is deprotonated by NaOEt to form an enolate, which undergoes a double S_N2 substitution with the ditosylate. The enolate carbon attacks C1 and C4 of the ditosylate, forming a cyclopen