There is not exactly such thing, but the Vala programming language is able to take a source code very similar to C#, and generate C codem or compile it directly.
http://live.gnome.org/Vala
Of course, the only problem are the libraries: C# has a lot of API's that you'll have to provide, or modify your source code to adapt to the Vala standard library.
If you wanted to translate this code to C because you need it compiled, there are other possibilities.
For example, ngen in the microsoft world:
http://msdn.microsoft.com/en-us/library/6t9t5wcf(v=vs.80).aspx
In the mono project, you can create a single exe file with the interpreter and the libraries. Look for mkbundle:
http://www.mono-project.com/Mono:Runtime
Mono is able to compile "ahead of time", i.e., generate the native code even before the program is going to be executed, so it will run faster.
http://www.mono-project.com/Mono:Runtime#Ahead-of-time_compilation