At the time of writing (November 2012) Windows Azure C# development is only available with the .NET 3.5 and 4.0 Frameworks. So what happens when you want to implement some asynchronous server-based programming using the .NET 5.0 Async language features?
Microsoft’s answer is to install the Async Targeting Pack for Visual Studio 2012. The only prerequisite is that you’re developing with Visual Studio 2012.
You can also install the package via NuGet using the following command in the Package Manager Console:
PM> Install-Package Microsoft.CompilerServices.AsyncTargetingPack
Once installed the following assembly will be referenced in your web role:
If you’d like to know more visit the …
- Official NuGet Async Targeting Pack for Visual Studio 11 
- Microsoft Download Center: Async Targeting Pack for Visual Studio 2012