Applications Of α-Oxo Ketene Dithioacetals As Odorless Thiol Equivalents In Thia-Michael Addition Reactions In Water

It is well-known that thiols are kind of versatile reagent and have been widely utillzed in organic synthesis. Thioacetals have been extensively investigated as carbonyl protection groups and versatile intermediates in the synthesis of multifunctional complex molecules and natural products. On the other way, Michael addition of thiols toα,β-unsaturated carbonyl compounds has emerged as one of the most convenient and efficient tools for the construction of carbon-sulfur bond and widely applied in organic synthesis. However, commonly used thiols, such as methanethiol, ethanethiol and benzyl mercaptan, having toxicity and a foul smell, can lead to environmental and safety problems. To resolve these drawbacks, some attempts have been made to develop odorless substitutes for these obnoxious thiols. As a result, a range of odorless or faint smell thiols have been prepared by increasing the alkyl chain length of thiol or introducing trialkylsilyl group into the benzene ring of benzyl mercaptan and benzenethiol.At the same time. organic solvent often appear in the traditional organic synthesis. From the green chemistry point of view, The organic reactions in water without the use of any organic solvent can also benefit from that water is an easily available, cheap, safe and environmentally benign solvent. Later on, extensive work has revealed that a variety of organic reaction sincluding Mukaiyama aldol reaction,allylation reactions,Diels-Alder reaction, Michael reactions, Manichtype reactions and even dehydration reaction can be realized in the presence of various catalysts such as inverse phasetransfer catalysts and surfactanttype Lewis or Bronsted acids in water.As a kind of versatile intermediates in trganic synthesis,α-oxo ketene dithioacetals habe been receibed considerable attention in recent years. During the course of our studies on the synthesis and applications ofα-oxo ketene-(S,S)-acetals, we found that this kind of compounds could be used as odorless thiol equivalents in thioacetalization and Michael additions. In the present work, we herein wish to report the investigations onα-oxo ketene dithioacetals as thiol equivalents in thia-Michael addition toα,β-unsaturated carbonyl compounds in water. This work mainly based on the following two aspects:(1) Due to the diversity ofα-oxo ketene dithioacetals,we do many organic reactions using different compounds in order to choose the most effectual one.At last ,we choose commercially available, odorless and stable 2-3-[bis(alkylthio) methylene]pentane-2,4-diones as thiol equivalents in thia-Michael addition toα,β-unsaturated carbonyl compounds.(2) We do a large number of reactions to search the appropriate condition including temperature, concentration of the catalyzer and so on.besides On the basis of the above experimental results together with our previous work, we give the mechanism for the thia-Michael addition reaction of 2-3-[bis(alkylthio) methylene]pentane-2,4-diones ? toα,β-unsaturated carbonyl compounds.In summary we have succeeded in exploring a new kind of reagents instead of thiols,moreover, which have been successfully applied on Michael addition reaction in water without the use of any organic solvent condition. This method is associated with some synthetic advantages, such as simple procedure, high yields and mild conditions. So the application ofα-oxo ketene dithioacetals in organic synthesis had been further developed, and which is propitious to environment and human due to escaping the use of toxic and foul smell thiols.