Thioketenes

Thioketenes are a class of organic compounds with the general formula R2C=C=S, where R can be hydrogen, alkyl, or aryl groups. They are the sulfur analogs of ketenes, where a sulfur atom replaces one of the oxygen atoms in the C=O double bond. Thioketenes are highly reactive species and are often generated in situ and immediately reacted further.

The synthesis of thioketenes can be achieved through various methods. One common route involves the thermolysis or photolysis of certain cyclic sulfur-containing compounds, such as 1,3-dithioles or related structures. Another method involves the dehydrohalogenation of thioacyl halides, similar to the synthesis of ketenes from acyl halides. The high reactivity of thioketenes makes their isolation challenging, and they are typically studied spectroscopically or trapped with reactive dienophiles or nucleophiles.

Due to their electrophilic carbon atoms and the presence of a cumulene system, thioketenes readily undergo cycloaddition reactions. They can react with dienes in [4+2] cycloadditions to form six-membered rings containing a thiocarbonyl group. They also participate in [2+1] cycloadditions with carbenes to form three-membered rings. Nucleophilic addition across the C=C=S system is also a characteristic reaction, leading to the formation of various sulfur-containing heterocycles or functionalized molecules. The study of thioketene chemistry provides insights into the reactivity of cumulenes and the synthesis of diverse organosulfur compounds.