Question

Extra Credit (5 points) In our section on alcohols, we learned about reactions of alcohols with toluenesulfonyl chloride to make tosylates. Sulfonyl chlorides also react with amines and nitrogen heterocycles to make sulfonamides. See starting material 1 below for an example of a sulfonamide. While tosylates are good leaving groups, sulfonamides are not. In fact, sulfonamides often serve as protecting groups for amines and nitrogen heterocycles. However, deprotection of sulfonamides is often challenging. The following deprotection of an indole derivative was conducted in my laboratories with only modest success. The desired (and deprotected) indole product 2 is formed in high yields. However, the indole product 2 cannot be separated from ethyl benzenesulfonate 3 by standard chromatographic techniques. As further information, we observe benzenesulfonic acid 4 (even though the reaction is conducted under rigorously anhydrous conditions, and an unknown low-boiling organic molecule as byproducts. OSiMezt-Bu OSIMezt-Bu OEt OEŚRO OH O=S=0 N Cs.co CO2Et THF/EIOH (solvent) heat + + a low boiling organic molecule -COEt OS=0 1 2 3 5 unable to separate by chromatography A. Draw a mechanism to account for the formation of 2 and 3 from 1. You may abbreviate the structure of 1 as shown in the box. R.R2 N O=SO B. The key to isolating 2 in pure form is the conversion of 3 to 4. 1) Draw a mechanism to account for this transformation; 2) draw the structure of compound 5; and 3) write the named reaction from this section of the course that this transformation most closely resembles.

Answer 1

EtOH + CO2 Eto + HCO3 OEt O Нco, 1 OEt OEt O -H O: + NI- 3