Acetone pinacol coupling

The Pinacol Coupling of acetone gives 2,3-dimethyl-2,3-butanediol which is also known as pinacol and the source of the name of this reaction ... 

In fact, diketones in a medium sized ring give several transannular reactions such as pinacol coupling [equation (i)] or aldolization [equation The later reaction also occurs during hydrogenation of aliphatic monoketones under favorable conditions (Pd-on-carbon, zeolite, 200°C, 4 X 10 kPa) to produce methyl isobutyl ketone from acetone (in 96%) -... 

More work has been reported on the inter- and intra-molecular pinacolic coupling of aldehydes and ketones, e.g. cycloheptanone and acetone gave (220) on treatment with a magnesium-mercury-titanium(iv) chloride reagent. ... 

A much more widely used reductive coupling is the pinacol coupling of carbonyl compounds, depicted below for acetone ... 

Reductive coupling Acetone Pinacol Formerly pilot plant Diamond Shamrock (US) BASF (FRG) 346,347 s... 

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. 

If the primary chemical process is still abstraction of a hydrogen atom to produce the benzophenone ketyl radical, one would expect to observe some mixed pinacol product arising from coupling of the benzophenone ketyl and acetone ketyl radicals,... 

Pinacol Acetone (Japan) BASF (West Germany) Past pilot-plant Reductive coupling... 

Pinacol reductive coupling.1 A couple prepared by sonication of zinc dust and CuCl2 in acetone-water (4 1) promotes coupling of enones and acetone to a, 3-unsaturated vic-diols. The reaction is slow in the absence of sonication. 

Tetraalkyl- and tetraatyl-ethylene glycols (pinacols) are made by reduction of ketones with active metals such as sodium, magnesium, and aluminum. The reaction is only fair for aliphatic and alicyclic ketones. Acetone, methyl ethyl ketone, cyclopentanone, and cyclohexanone all give less than 0% yields of pinacols. Mixtures of ketones are reduced to unsymmetrical pinacols. An active zinc-copper couple has been employed in the reduction of several simple olefinic aldehydes to dieodiols, e.g., crotonaldehyde to dipropenyl glycol,... 

The reductive coupling reaction of ketones has been carried out in Germany at BASF on an electrolytic pilot plant where pinacol was obtained from acetone and at Sorapec in France where the pinacol of 4-hydroxy-propiophenone was also produced on a pilot plant. This type of reaction would appear to be easier to perform by electrolytic methods than by catalytic methods in which the alcohol is the favoured product. 

Dimethyl-1,3-butadiene is produced by dehydration of pinacol, which in turn is made by reductive coupling of acetone, followed by purification via sulfur dioxide adducts [313]. It can be polymerized radically (emulsion polymerization), anionically, cationically, or by coordinative catalysts [314-319]. Due to the sterical hindrance of two methyl groups. 

The ready availability of arylboronates by an aromatic C-H borylation provides a synthetic link to the well-established palladium-catalyzed cross-coupling reactions, rhodium-catalyzed 1,4-addition to a,p-unsaturated carbonyl compounds, and other bond forming reactions using arylboronic esters (Scheme 2.12). Borylation of 1,3-dichlorobenzene with pinacolborane is followed directly by a cross-coupling reaction with methyl p-bromobenzoate for the synthesis of a biaryl product in 91% yield [60]. Pinacol esters of arylboronic acids react much slower than the free acids [62], but both derivatives achieve high isolated yields and comparable enantioselectivities (91% ee) in asymmetric 1,4-addition to N-benzyl crotonamides [63]. Borylation of arenes followed by oxidation of the C-B bond is synthetically equivalent to an aromatic C-H oxidation to phenols [64]. Oxidation of the resulting arylboronates with Oxone in a 1 1 acetone-water solution is completed within 10 min at room temperature. 

The couple Zn-Cu also promotes the pinacol reductive cross-coupling between saturated and a,p-unsaturated carbonyl compoimds in aqueous heterogeneous media. The reaction between a,P-unsaturated cycloalkenones and acetone is accelerated by US irradiation and is significantly influenced by the Zn/Cu and Zn/substrate ratios [81]. 

Ring-expansions have been used in two syntheses of the monoterpene kara-hanaenone (12). In the first, the interest lies in the regioselectivity of the addition of thiophenol to the allene (13) and the rapid Cope rearrangement of the cis-product (Scheme 20), whilst in the second the availability of the pinacolic intermediate relies on the success of the titanium-mediated coupling of acetone with the requisite cyclohexanone [equation (17)]. ... 

---