Proper syntax to assign std::vector to a specific memory location on the heap?

I am trying to implement the directions in these two SO posts regarding assigning containers to specific memory locations on the heap:

1. Moving C++ objects, especially stl containers, to a specific memory location
2. Create objects in pre-allocated memory

However, I must be doing something stupid (I'm new to C++) because I can't even get my code to compile (using C++ 11 as you can see below):

  std::vector<int> ints1 = {10, 20, 30};
  ints1.reserve(20);
  auto adr = &(*ints1.end());
  auto *ints2 = new(adr)(std::vector<int>(20);

I am getting an error of a expected , or ; before ) for the last line, which I take to mean that my syntax is just wrong, but how?

Also, once I fix this syntax, what's the best way to ensure these objects really are contiguous? I thought I would ensure that

&(*ints1.begin()) - &(*ints2.begin) is roughly on the order of sizeof(std::vector<int> v(20));

Is there a better way?

(p.s. I do realize I should allocate the memory I am going to use to do this to avoid undefined behavior)