acetonide protection mechanism

acetonide will form a dioxolane selectively over a dioxane. Isopropylidenes (acetonides): OO R1R2 HOOH R1R2 Acid Acetone or OMe or OMe OMe.

However, the conversion of hemiacetals into acetals is catalyzed only by acids (Eqs. ZrCl 4 was an efficient catalyst for the deprotection of 1,3-dioxalanes, bis-TBDMS ethers, and diacetate functional groups in excellent yields. This is achieved by refluxing with a large excess of the acetonide reagent. 19.47b and c). Acetonide is a common protecting group for 1,2- and 1,3-diols.

Transketalation is the method of choice when acetals (ketals) with methanol are desired. Ph Ph Ph Theprotectinggroupsthatmask1,2-and1,3-diols(formingeitherthe dioxolane or dioxane, respectively) are often referred to (PREFIX)ylidenes, where the prefix depends on the nature of R and R 1.

There are two general methods for the introduction of this protection. Protection of 1,2 & 1,3-diols 1,2-acetonide formation is usually favored over 1,3-acetonides Cleavage: Mild aqueous acid OO R1R2 R3R4 HOOH R1R2 O R3R4 Acid 1. OO OO … Protection.

ZrCl 4 also promoted diol protection as the acetonide in very good yields and acted as a transesterification catalyst for a range of esters. Protection of 1,3-Diol • Benzaldehyde acetal • di-tert-Butyl dioxasilinane 46. The protecting group can be removed by hydrolysis of the ketal using dilute aqueous acid.. S. Singh, C. D. Duffy, S. T. A. Shah, P. J. Guiry, J. Org. 19.10 ACETALS AND THEIR USE AS PROTECTING GROUPS 923 The formation of hemiacetals is catalyzed not only by acids but by bases as well (Problem 19.16b, p. 910). Example. In organic chemistry, an acetonide is the functional group composed of the cyclic ketal of a diol with acetone.The more systematic name for this structure is an isopropylidene ketal.

(a) Acetonide protecting groups were installed to protect the hydroxyl groups from oxidation in steps 3 to 4.
Protection of 1,2-Diol Acetonide protection • Benzaldehyde acetal • Acetonide 45. Chem., 2008, 73, 6429-6432. Acetone is the by-product, which has to be removed to shift the equilibrium to the right hand side. 1,3 diols are usually protected with benzaldehyde but why is acetone is used only for 1,2 diols ?

Protecting Groups: A Necessary Evil 3 Note, however, that each protecting group incorporated in a multi-step synthesis increases the synthesis by two non-productive steps reducing the overall yield and efficiency of the synthesis.

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