N-Carbamate Protecting Groups

Jones conditions), aqueous acid, and mild Lewis acids.The Boc group is usually removed by treatment with aqueous HCll or with anhydrous trifluoroacetic acid. In Lai s synthesis of indole analogs of mycophenolic acid, indole derivative 143 was converted to the N-Boc compound (144) using Boc anhydride. Elaboration of the side chain in three steps was followed by deprotection with HCl in dioxane, giving 145 in 72% yield. Trifluoroacetic acid in dichloromethane converted 145 to 146 in 60% yield. 

In a synthesis of 4-hydroxypipecolic acid, Varela and co-workers protected the primary amine unit in 147 as the benzyl carbamate (148).Manipulation of the protected diol led to the primary mesylate in 149, and catalytic hydrogenation removed the Cbz group to give the primary amine in 150. 

In the transformation of A to B and then to C from the synthesis of 7-deoxypancratistatin, in Section 7.3.A.i., deprotection was followed by conversion of a lactone to a lactam. Provide a mechanism for the deprotection of both the O—MOM group and the dioxolane, giving a triol, and also for the lactone-lactam conversion in the second step. 

In each of the following, give the major product. If there is no reaction, indicate by N.R. Show stereochemistry where it is appropriate. 

For each of the following, determine if protection is required in the given sequence. If so, choose the protecting group(s), explain your choice(s), and provide all necessary reagents for the entire sequence. 

---