Ketals formation, partial

First the isopropylidene ketal at C-3b and C-4b is generated using acetone and an ion-exchange resin at first. There is no further ketal formation at other positions of the lactose. It is also possible to use 2,2-dimethoxypropane (Me)2C(OMe)2 instead of acetone. The problem in this step is the partial formation of hemi-ketals with the other hydroxy groups which lower the yield. They are destroyed by heating to 100 °C in glacial acetic acid.20... 

Clarl997 Clarke, I.D. and Hodge, R, Partial Separation of Enantiomeric 1,2-Diols via Ketal Formation with a Polymer-Supported Chiral Ketone, J. Chem. Soc., Chem. Commun., (1997) 1395-1396. 

The direct formation of a dimethyl ketal by reaction of the ketone with methanol is particularly sensitive to steric effects. Only cyclohexanones react under these conditions.In the steroid series only saturated 3-ketones form dimethyl ketals with methanol and acid although partial reaction of a 2-ketone has been observed in the presence of homogenous rhodium catalyst. ... 

The mechanism presumably involves partial opening of the ketal to permit enol formation, followed by bromination and reclosing of the ketal ... 

The reaction is catalyzed by Co carbonyls using reaction conditions in the range 200-250 bar and 175-210°C, and, when first reported, was characterized by both low yields (maximum 42%) and a spectrum of by-products including acetaldehyde, methyl formate, methyl acetate, propanol, butanol, and methane (17). Subsequently, catalytic activity toward hydrocarbonylation has been demonstrated with other metals, although Rh, usually appreciably more active than Co in other synthesis gas reactions, produces acids and esters, and ethanol only comprises a significant product at high H2 partial pressures. Methanol hydrocarbonylation may also be carried out with Fe or Ru catalysts promoted by tertiary amines, but the rates are even lower than with Co, which remains the preferred choice. The reaction rate is accelerated by the presence of promoters such as I , in which case acetaldehyde (which may also be obtained from the Co/I -catalyzed reaction of synthesis gas with methyl ketals or methyl esters (18)), comprises the major product. 

Barium hydroxide dimethylf ormamide Reactions with simultaneous etherification and esterification Goumarin ring opening Benzilic acid rearrangement Partial formation of ketals... 

The C-14 epimeric compound (XXVI) was obtained by partial dioxolanation of the stable diketone XXII-A. Either ketal on treatment with p-toluenesulfonic acid in benzene produced an equilibrium mixture of the two, XXV and XXVI, in nearly equal quantities. The equilibrium is presumably established by the formation of the enol ether XXVII. Thus the configuration at C-14 which is strongly favored in the diketone... 

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