yes, Mainsoft Grasshopper. But given that the CLR is superset of JVM features, you can't easily convert .NET MSIL to Javabyte code (a few research projects tried but it's not pratical). Grasshopper did it at a language level and wrote a C# to Java bytecode compiler.

However going the other direction is really easy and straight forward. IKVM.NET has been running Java on top of .NET for years.