One of the most important thing to remember when decorating a method with async is that at least there is one await operator inside the method. In your example, I would translate it as shown below using TaskCompletionSource.
private Task<int> DoWorkAsync()
{
//create a task completion source
//the type of the result value must be the same
//as the type in the returning Task
TaskCompletionSource<int> tcs = new TaskCompletionSource<int>();
Task.Run(() =>
{
int result = 1 + 2;
//set the result to TaskCompletionSource
tcs.SetResult(result);
});
//return the Task
return tcs.Task;
}
private async void DoWork()
{
int result = await DoWorkAsync();
}