Acidolysis proton generation

FIGURE 3.6 Deprotection of functional groups by acidolysis. Protonation followed by carbocation formation during the removal of ferf-butyl-based protectors by hydrogen chloride.8 One mechanism is involved in generating the ferf-butyl cation, which is the precursor of two other molecules. 

FIGURE 3.5 Deprotection of functional groups by acidolysis.5 Protonation followed by car-bocation formation during the removal of benzyl-based protectors by hydrogen bromide. Two mechanisms are involved in generating benzyl bromide from the protonated substrates. 

Catalytic reactions were performed in CH2C12 under an 02 atmosphere Zn was used as an electron source and acetic acid as a proton donor (14). Under these reaction conditions ([2] [substrate] = 1 125), the production of adamantan-l-ol (248%), adamantan-2-ol (50%), and adamantan-2-one (108%) was observed. With cyclohexene as substrate, a mixture of cyclohexanol (54%), cyclohexanone (73%), and cyclohexene oxide (20%) was generated. In a similar experiment with cyclohexane, cyclohexanol (99%), and cyclohexanone (84%) were obtained. The product distribution is inconsistent with a free radical process for ada-mantane, the 3°/2° carbon reactivity ratio is 2.2. Control experiments demonstrated that both Zn dust and acetic acid were necessary, whereas larger quantities of acetic acid quenched the reaction (Table II). This may be due to the acidolysis of the n-oxo bond. Simple monomeric complexes such as FeClTPP (TPP is tetraphenylporphin), Fe(acac)3 (acac is acetylacetonate), and [Fe(HBpz3)2]+, 3, were inactive as catalysts under identical conditions. Furthermore, [Fe3+(Salen)]20, 1, did not show any reactivity. 

In order to design syntheses of complex peptides containing several functional side chains, it is necessary to have a variety of methods of protection and deblocking at disposal. Therefore, it was a major step forward when in addition to reduction and acidolysis deprotection with weak bases, under mild conditions, became a practical possibility. The 9-fluorenylmethyloxycarbonyl (Fmoc) group (Carpino and Han 1970) is removed from the amino group by proton abstraction with secondary amines. A carbamoic add is generated, that, in turn, loses carbon dioxide and affords the free amine ... 

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