Electro‐Deprotection—Electrochemical Removal of Protecting Groups

Abstract

The reactions of electrochemical splitting may be successfully used for removal of protecting groups. Theoretical and preparative aspects of the method of electro‐deprotection are discussed, and examples of its use are given. The removal often requires high potentials. The use of modified protecting groups (“inner activation”) or of catalysts (electron carriers) which facilitate electron transfer against the standard potential gradient (“external activation”), can greatly increase the scope of the electrochemical method.

Electrochemistry in a Divided World

“…Soon were obtained hopeful results, e.g., [280,281], successfully presented abroad (England [282,283], India [284], Bulgaria, Romania, Hungary, and East Germany). It concerned plastic-bonded cadmium and nickel oxide electrodes.…”

“…This happened at the time of the so-called Doctor's plot, when medical doctors of Jewish origin were blamed of attempting the assassination of Soviet leaders. The most important results, which are still valid, from the period 1944 to 1961 concerned the mechanism of polarization of a Ni-anode during the oxygen evolution reaction involving the participation of Ni(III) and Ni(IV) oxides [277][278][279][280]. Parallel to these studies, in 1946 Tur'yan started to use more and more polarography to study chemical reactions.…”

“…Later, we propagate this technique to a great number of other groups [279,280]. In most cases, the process was carried out under рН control (Sect.…”

“…9.2.1, "Electrolysis at a Constant "pH" ("pX") with Recording Equipment"). The HOMEC is also efficient for labile substrates and for difficult reducible (oxydable) groups [279][280][281]. For example, the HOMEC's electron transfer beyond the supporting electrolyte discharge region was used to obtain glycine from its Z derivate with quantitative yield.…”

High yield protection of alcohols, including tertiary and base sensitive alcohols, as benzhydryl ethers by heating with diphenyldiazomethane in the absence of any other reagent

“…The protecting group in benzhydryl ethers and amines can be cleaved by hydrogenolysis, 30,31 acid hydrolysis 32,33 or oxidation; 34 more specialised methods, such as the ozone cleavage of benzhydryl aziridinyl esters, can be used where the circumstances warrant. 35 Acetonides or benzylidene acetals can be removed selectively without affecting the benzhydryl ether by acid hydrolysis; for example, the fully protected lyxonolactone 19L on treatment with 80% aqueous acetic acid gave the benzhydryl lactone 20L {oil, ½a 20 D +24.3 (c, 1.81)} in 87% yield (Scheme 3).…”