Protection for the Hydroxyl Group Esters

Reactivity Chart 2. Protection for the Hydroxyl Group Esters 

Formate Ester 3. Acetate Ester 6. Trichloroacetate Ester 10. Phenoxyacetate Ester 19. Isobutyrate Ester 

6-Trimethylbenzoate (Mesitoate) Ester 34. Methyl Carbonate 36. 2,2,2-Trichloroethyl Carbonate 39. Allyl Carbonate 

---

A nitrophenylsulfenate, cleaved by nucleophiles under very mild conditions, was developed as protection for a hydroxyl group during solid-phase nucleotide synthesis. The sulfenate ester is stable to the acidic hydrolysis of acetonides. ... 

Tetrahydropyranyl (THP) ethers are frequently used as a protecting group for the hydroxyl group. Their formation and cleavage from alcohols and phenols have been successfully catalyzed by Bi(N03)3 5H20 [92] and Bi(0Tf)3 %H20 [93]. The conversion of THP ethers to acetate and formate esters has been reported to be efficiently catalyzed by Bi(0Tf)3 xH20 [94]. 

Aminoalcohols are an important class of compounds in medicinal chemistry because many drugs contain this structure. For their resolution, there are two possibilities acylation of amino function or an enzymatic transesterification with vinyl esters through the hydroxyl group. However, the amino or hydroxyl group must be protected, because if the starting material is the free aminoalcohol, the O- and N-acylation can take place, and in addition, there are migrations obtaining... 

While in the uncatalyzed reaction of l-ethyleneimino-2-hydroxy-3-butene in THF, refluxing for four hours was necessary to produce 70% of the ester, in the presence of NaNH2 a 90% yield was achieved at room temperature after only five minutes.[13 14] An especially interesting example of the use of the imidazolide method for ester synthesis is illustrated by the total synthesis of actinomycin C3.[15],[16] Working with N-protected L-TV-methylvaline and CDI, esterification of the hydroxyl group on the threonine residue proved successful whereas this could not be accomplished by any of the conventional methods. 

---