Pinacol diacetate

A soln. of 9-diazofluorene in dimethylformamide added dropwise with stirring at 40° under N2 to a soln. of cupric acetate in the same solvent, warming and stirring continued 18 hrs. until Ng-evolution ceases -> fluorenone pinacol diacetate. Y 55%. F. e., also formation of sym. ethylene derivs. (cf. Synth. Meth. 18, 862) with cupric tartrate, s. T. Shirafuji, K. Kitatani, and H. Nozaki, Bull. Chem. Soc. Japan 46, 2249 (1973). 

A further method permits stereoselective conversion of cis-l,2-diol diacetates into acetoxonium derivatives it involves reaction with liquid hydrogen fluoride. Thus, cis-l,2-diacetoxycyclopentane (16) reacts rapidly in liquid hydrogen fluoride to give the ion 15. trans-1,2-Diacetoxycyclopentane (14), on the other hand, is converted" only very slowly (72 hours) into 15. Similarly, cis-l,2-diacetoxycyclohexane (19) is rapidly converted into the ion 18, whereas the corresponding trans derivative does not react.Such acyclic derivatives as 5 react relatively slowly, to give the corresponding ion (2). Pinacol, in acetic anhydride and in the presence of 70% perchloric acid, can be converted into the acetoxonium perchlorate. This reaction is, presumably, comparable to the reaction with hydrogen fluoride. 

AC2O or AcCl can be utilized instead of a chlorosilane in the VOCU-catalyzed pinacol coupling reaction of aromatic aldehyde to give the diacetate 32 (Scheme 2.22) [70]. As mentioned above, a low-valent vanadium catalyst appears... 

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