Acetolysis reaction, acid-catalyzed

As slight variations in acidity are sufficient to markedly alter the rate, some problems with the reproducibility of the acid catalyzed acetolysis may be encountered. Careful monitoring of the reaction by 1H NMR spectroscopy, in preferance to TLC, is recommended [202],... 

Bicyclopentane reacted with acetic acid at 86 °C to give acetoxycyclopentane (27 a, 47%) and cyclopentene (29a, 53%). In the presence of /7-toluenesulfonic acid a substantial amount of tosyloxycyclopentane was isolated. Deuterio- and methyl-substituted bicyclo[2.1.0]pentane derivatives were submitted to acid-catalyzed and uncatalyzed acetolysis reactions. The distribution of products was analyzed and the rates of reaction calculated. It was shown that the acetolysis of the extremely strained bicyclopentane proceeds mainly via inversion of configuration at both ends of the central bond when it was cleaved. 5,5-Dimethylbicyclo[2.1.0]pentane (31) reacted via cleavage of one of the outside C —C bonds, leading to 1-cyclobutyl-1-methyl-ethyl products 33, rather than via cleavage of the central bond. ... 

The radical mechanism was justified by the polymerization of various olefins by the [Pb(CH3)4 + Cu(NOg)2] system, but not by methylcopper. Recently, Clinton and Kochi 49, 50) have reexamined each stage of the reaction for tetraethyllead in acetic acid solution. The decomposition was strongly catalyzed by copper(I), and acetolysis was found to occur by a metastable intermediate, ethylcopper ... 

It has been shown that the acetolysis of methyl tri-0-acetyl-/S-D-arabino-pyranoside, when catalyzed with zinc chloride or 0.16% sulfuric acid, provides a mixture of the two isomeric penta-O-acetyl-n-arabinose methyl hemiacetals in good yield.This reaction provides good evidence for the cleavage of the cyclized bond in preference to that of the glycosidic group. 

---