New Synthetic Methods and Reactions Involved the Dithioacetal Functionality

The new synthetic methods and applications of dithioacetal are fully described in this thesis.
Firstly, we founded that the carobn-sulfur bonds of aliphatic dithioacetals could be efficiently activated by electron-donating trialkylphosphine ligands. In the presence of suitable nickel catalyst and without the chelation effect of special designed dithioacetals, simple aliphatic dithioacetals could react with a series of Grignard reagents to give the corresponding olefinic products. By using this methodology, alkenyl silanes which have useful applications from a synthetic point of view could be easily obtained.
The second part is about the carbon-carbon bond forming reaction. In order to solve the problem on the synthesis of propargylic dithioacetals, we try a new route for this synthesis by the corresponding terminal alkyne via transition-metal catalyzed cross-coupling reactions. During the study of this topic, we have developed palladium-catalyzed cross-coupling reactions of alkynyl nucleophiles and alkyl halides. In the presence of palladium catalyst and triphenylphosphine, alkynyl Grignards or alkynyllithiums could successfully couple with alkyl bromides and iodides. Aryl-substituted propargylic dithioacetals could also be obtained by this strategy. However, alkyl-substituted propargylic dithioacetals could be synthesized by the displacement reaction of the corresponding terminal alkynes with alkyl iodides.
The last part is concerning the new application of dialkyl-substituted propargylic dithioacetals. The beta-thioalkoxyalcohols could be obtained in good yields by the reaction of dialkyl-substituted propargylic dithioacetals with a series of carbonyl compounds. The carbon-sulfur bond of beta-thioalkoxyalcohol can be activated in the presence of iron salt and Grignard reagent. The active intermediate is found to undergo beta-OMgI elimination and give the corresponding enyne.