Commonly used reagents—-PPTS_industrial additives

Pyridine-p-toluenesulfonate (PPTS) is a widely used, mild, acidic catalytic reagent commonly used in laboratories in organic synthesis. PPTS can simply be regarded as a substitute for p-toluenesulfonic acid, and all reactions completed by p-toluenesulfonic acid can also be completed by PPTS. But it has more advantages in use than p-toluenesulfonic acid. For example: p-toluenesulfonic acid generally exists and is used in the form of monohydrate crystals, while PPTS is anhydrous; p-toluenesulfonic acid has strong acidity. The acidity of PPTS does not have a significant impact on many acid-sensitive functional groups.

Reactions catalyzed by PPTS usually feature simple and mild reaction conditions, and the dosage is generally within 30 mol%. The two most widely used reactions are the acetalization reaction of hydroxyl groups and the silyl etherification reaction of hydroxyl groups, as well as the reverse reactions of these two reactions, so it is widely used in the protection and deprotection reactions of hydroxyl groups [2]. Using different reaction solvents, PPTS can catalyze the acetalization reaction and silicon etherification reaction of hydroxyl groups; it can also catalyze their reverse reactions. The former is usually carried out in CH2Cl2 or DMF solvent, and the latter usually uses MeOH as the solvent (Formula 1, Formula 2) [3,4].

Using an excess of reagents can generate multiple acetals or multiple silyl ether protecting groups from multiple hydroxyl substrate molecules at one time (Formula 3)[5,6]. Appropriate reaction conditions can also be selected to achieve selective desilylation of polysilyl ether substrate molecules [7]. Through clever design, the desilylation reaction of the hydroxyl group and the acetalization reaction of the hydroxyl group can be realized sequentially in the same reaction (Formula 4) [8,9].

PPTS can also catalyze a type of tandem reaction with high synthetic value, that is, after the desilyl ether reaction, the free The hydroxyl group then undergoes an intramolecular acetalization reaction again to form a new heterocyclic product (Formula 5) [7]. If there is an ester group at an appropriate position in the substrate molecule, intramolecular esterification can occur to generate the corresponding lactone (Formula 6) [10,11].

References

1. Freeman, F.; Kim, D. S. H. L.; Rodriguez, E. J. Org. Chem ., 1992, 57, 1722.

2. Greene, T. W.; Wuts, P. G. M. Hand-feeling Groups in Organic Synthesis, 3rd ed.; John Wiley & Sons, Inc.: New York, 1999.

3. Matsuya, Y.; Sasaki, K.; Nagaoka, M.; Kakuda, H.; Toyooka, N.; Imanishi, N.; Ochiai, H.; Nemoto, H. J. Org. Chem ., 2004, 69, 7989.

4. Li, Z.; Baker, D. L.; Tigyi, G.; Bittman, R. J. Org. Chem., 2006, 71, 629.

5. Keller, V. A.; Kim, I.; Burke, S. D. Org. Lett., 2005, 7, 737.

6. Adams, C. M.; Ghosh, I.; Kishi, Y. Org . Lett., 2004, 6, 4723.

7. Blakemore, P. R.; Browder, C. C.; Hong, J.; Lincoln, C. M.; Nagornyy, P. A.; Robarge, L. A.; Wardrop, D. J.; White, J. D. J. Org. Chem., 2005, 70, 5449.

8. Jin, M.; Taylor, R. E. Org. Lett., 2005, 7, 1303.

9. Shoji , M.; Imai, H.; Mukaida, M.; Sakai boron trifluoride tetrahydrofuran complex, K.; Kakeya, H.; Osada, H.; Hayashi, Y. J. Org. Chem., 2005, 70, 79 .

10. Ramana, C. V.; Srinivas, B.; Purani, V. G.; Gurjar, M. K. J. Org. Chem., 2005, 70, 8216.

11. Sato , K.; Sasaki, M. Org. Lett., 2005, 7, 2441.

This article is reproduced from: “Modern Organic Synthetic Reagents—Properties, Preparation and Reactions”, edited by Hu Yuefei and others