In each of the following reactions, the glycosyl donor is activated by reaction with an

Problem 23.43 Chapter 23

Organic Chemistry, | 9th Edition

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Problem 23.43

In each of the following reactions, the glycosyl donor is activated by reaction with an electrophilic reagent by the general pathway: Glycosyl donor C6H5CH2O C6H5CH2O C6H5CH2O E Y CH2OCH2C6H5 X O C6H5CH2O C6H5CH2O C6H5CH2O E CH2OCH2C6H5 X O C6H5CH2O C6H5CH2O C6H5CH2O CH2OCH2C6H5 OR O Oxygen-stabilized carbocation ROH glycosyl acceptor O C6H5CH2O CH2OCH2C6H5 C6H5CH2O C6H5CH2O The oxygen-stabilized carbocation that is formed reacts with the glycosyl acceptor ROH to form an anomeric mixture of O-glycosides. Using curved arrows, write a mechanism to show how each of the glycosyl donors produces the oxygen-stabilized carbocation. For part (a) consult Section 16.16 on sulfides and 8.11 on triflates; for part (b) examine step 2 in Mechanism 19.6, and assume that silylation occurs at nitrogen in the glycosyl imidate ester.

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