Dimethylbutane-2,3-diol

As reductions by metals often occur by one-electron transfers, radicals are involved as intermediates. When the reaction conditions are adjusted so that coupling competes favorably with other processes, the formation of a carbon-carbon bond can occur. The reductive coupling of acetone to 2,3-dimethylbutane-2,3-diol (pinacol) is an example of such a reaction. 

A reaction that follows this pattern is the acid-catalyzed conversion of diols to ketones, which is known as the pinacol rearrangement.60 The classic example of this reaction is the conversion of 2,3-dimethylbutane-2,3-diol(pinacol) to methyl /-butyl ketone (pinacolone).61... 

Rearrangements may also proceed via intermediates that are essentially cations, anions, or radicals, though those involving carbocations, or other electron-deficient species, are by far the most common. They may involve a major rearrangement of the carbon skeleton of a compound, as during the conversion of 2,3-dimethylbutan-2,3-diol (pinacol, 42) into 2,2-dimethylbutan-3-one (pinacolone, 43, cf. p. 113) ... 

Dodecafluoro(2,3-dimethylbutane-2,3-diol) reacts with sulfur tetrafluoride in an unconventional way instead of replacement of the hydroxy groups by fluorine, the substitution of four fluorine atoms in the sulfur tetrafluoride molecule by oxygen occurs to give a good yield of perfluorinated spiro-A4-sulfane 8.62... 

The example shows the dimerization of acetone to give a diol (2,3-dimethylbutane-2,3-diol) a. i, . , whose trivial name, pinacoi, is used as a name for this type of reaction using any ketone. Sometimes... 

An acyclic precursor devised by Bogndr and Herczegh, prepared via oxidative cleavage of the furane nucleus, has been applied in the synthesis of racemic pentoses. 2-(2-Furyl)-4,4,S,S-tetramethyl-l,3-dioxolane 257 obtained in reaction of furfural with 2,3-dimethylbutane-2,3-diol was chosen as a substrate, owing to its stability in acidic media (at pH > 3). Oxidation of 257 with bromine water gave the unstable endialone derivative 258, which was reduced with sodium borohydride to 259 (isolated as crystalline dibenzoate). Epoxidation of 259 gave... 

The first pinacol rearrangement was conducted by Fittig in 1860, though he did not know the precise constitutions of the starting material and product at the time of the experiment. On treatment of 2,3-dimethylbutane-2,3-diol (pinacol) with sulforic acid, 3,3-dimethylbutane-2-one (pinacolone) was formed. ... 

A much more common rearrangement (the pinicol rearrangement) is depicted as item 6 in Table 8.7. The particular case shown in item 6 bears the overall responsibility for the generic type of reaction (i.e., 2,3-dimethylbutan-2,3-diol, the trivial name for which is pinacol, is converted to 3,3-dimethyl-2-butanone, the trivial name for... 

Dimethylbutane-2,3-diol has the common namepinacol. On heating with aqueous acid, pinacol rearranges to pinacolone, 3,3-dimethyl-butan-2-one. Suggest a mechanism. 

The above rule easily predicts this result. We must take note that the secondary alcohol group is transformed into formic acid, which can be determined by pro-tometry (as we have seen). Likewise, with the same mle, we immediately find that 2,3-dimethylbutane-2,3-diol gives two molecules of acetone ... 

The photolysis of propanone in propan-2-ol results in hydrogen atom transfer to the ketone and two identical ketyl radicals are formed. The formed ketyl radical undergo disproportion and dimerisation reaction to get stabilised. The photolysis yields 2,3-dimethylbutan-2,3-diol (pinacol) as the sole product of the reaction. 

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