
TY  - JOUR
A1  - Kuszmann, J 
A1  - Gacsbaitz, E 
T1  - O-Benzylidene Derivatives of D-Arabinose Diethyl and Dipropyl Dithioacetal
JF  - Australian Journal of Chemistry
JO  - Aust. J. Chem.
Y1  - 1996
VL  - 49
IS  - 3
SP  - 273
EP  - 280
KW  - 
UR  - https://doi.org/10.1071/CH9960273 
N2  - Benzylidenation of D-arabinose diethyl and dipropyl dithioacetals with &#945;,&#945;-dimethoxytoluene in the presence of p-toluenesulfonic acid has been studied in detail. Under kinetic control the two terminal dioxolan -type 4,5-O-(R)- and 4,5-O-(S)-benzylidene  diastereomers are formed first which are in equilibrium with each other In the thermodynamic phase of the reaction the corresponding dioxan -type 3,5-O-(R)- benzylidene isomer is formed too, but all three monobenzylidene isomers are gradually converted into the four possible dioxolan -type 2,3 : 4,5-di-O benzylidene diastereomers . The dioxan -type 2,4:3,5-di-O-benzylidene isomer was present only in trace amounts. When benzaldehyde was used as reagent in the presence of hydrochloric acid or zinc chloride only the 2,3: 4,5-di-O-benzylidene diastereomers were formed. Partial hydrolysis of the dibenzylidene derivatives yielded the corresponding 2,3-O-benzylidene diastereomers. Structures, including the chirality of the benzylidene groups, were determined by n.m.r. spectroscopy. A mechanism suggested for the reaction was partially supported by equilibration studies. 
ER  -

