Aldrich ChemFiles 2007, 7.3, 6.

Aldrich ChemFiles 2007, 7.3, 6.

Recent work by David Crich has been focused on the application of propargyl ethers as sterically unobtrusive donor protecting groups for b-mannosylation.1 The propargyl ethers were easily introduced, and produced the desired effect on the stereoselectivity of the b-mannosylation reaction; however, they required an unwieldly two-step deprotection requiring the use of OsO4. Further research elucidated the use of 3-(1-naphthyl)- 2-propynyl ethers as a protecting group that retained the advantages of the propargyl ethers, yet were cleavable in a single step, orthogonal to benzyl ethers.2

Hydroxy groups on a carbohydrate are easily alkylated with 1-(3- bromo-1-propynyl)naphthalene and sodium hydride to yield the propargyl ether. Subsequent deprotection is easily achieved by treatment with DDQ in wet dichloromethane over the course of 2-3 hours (Scheme 1). Furthermore, the propargyl ether proved to be exceptionally b-selective in glycosylations.

Scheme 1

The hydroxy precursor, 3-(1-naphthyl)-2-propyn-1-ol is also useful as a building block. For example, a report from Tanaka details the use of 3-(1-naphthyl)-2-propyn-1-ol in a rhodium-catalyzed crosscyclotrimerization with dimethyl acetylenedicarboxylate to furnish the axially chiral biaryl in good yield and excellent enatioselectivity (Scheme 2).3

Scheme 2

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  1. (a) Crich, D.; Jayalath, P. Org. Lett. 2005, 7, 2277. (b) Crich, D. et al. J. Org. Chem. 2006, 71, 3064.
  2. Crich, D.; Wu, B. Org. Lett. 2006, 8, 4879.
  3. Tanaka, K. et al. Org. Lett. 2005, 7, 3119.

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