3,4-dihydro-2H-pyran → (2R)-2-[(tert-butoxycarbonyl)amino]-3-(tetrahydro-2H-pyran-2-yloxy)propanoic acid

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Reaction Steps

To a stirred solution of 2.32 g (0.012 mol) of p-toluensulfonic acid and 0.95 g (0.012 mol) of pyridine in 250 mL of dichloromethane, 25.0 g (0.12 mol) of Intermediate 1 was added. Then, 24.22 g (0.29 mol) of dihydropyran was added dropwise and the resulting mixture was stirred overnight at room temperature. The solvent was removed under vacuum and the residue was redissolved in ethyl acetate (350 mL). The organic phase was washed with water (2×250 mL) and dried over sodium sulphate. The solvent was evaporated under vacuum and 49.00 g of a pale yellow oil was obtained. The oil was not purified and used directly in the following step.

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