Studies On Deprotection Of Silyl Ethers And Benzylidene Of Silyl Carbohydrates

Hydroxyl groups are ubiquitous in organic compounds.Some of these compounds are bioactive or important in organic synthesis,such as natural products steroids,nucleosides,carbohydrates,some amino acids and so on.There are many methods for the protection of hydroxyl group,such as the formation of ethers,silyl ethers,acetates and so on.The often used method is to convert alcohol to silyl ether using t-butyldimethylsilyl chloride because silyl ethers are invulnerable to acids and bases to a certain degree,and can be easily deprotected with various methods when using such catalysts as AcOH,ZrCl₄ at room temperature.However,there are certain drawbacks related to these methods.Therefore,a novel method for the deprotection of silyl ethers has been developed using a molecular organocatalyst?MeSCH₂Cl/KI?in this article.Firstly,silyl ether was synthesized using the reported experimental method.Then,the optimized desilylation conditions were determined after exploring the effect of reaction temperature,solvents,the amount of catalysts and water on the reaction system.Finally,the method was further applied to eight substrates.The formation of benzylidene acetals is widely used to protect the 4-and 6-hydroxyl groups of carbohydrates because the acetals are easy to be synthesized,unsusceptible to bases and oxidizing agents,easy to be removed by hydrogenolysis under neutral conditions or hydrolysis with acids,and can be converted to other carbohydrate derivatives.In order to further apply the new catalyst?MeSCH₂Cl/KI?to organic synthesis,a new method has been developed for benzylidenation.Firsly,methyl 6-O-?t-butyldimethyl silyl?-?-D-glucopyranoside was synthesized using the reported experimental method.Then,the optimized conditions were determined after exploring the effect of the amount of catalysts and benzaldehyde on the reaction system.Finally,the method was applied to five substrates for the synthesis of benzylidene acetals.Notably,When p-fluorobenzaldehyde was used,corresponding p-fluorobenzylidene acetals were successfully synthesized with twelve substrates.A possible S_N2 reaction mechanism is proposed according to the experimental phenomena,results and control experiments.