The command toeplitz
does exactly what you want:
toeplitz([1,2,3,4,5,6])
ans =
1 2 3 4 5 6
2 1 2 3 4 5
3 2 1 2 3 4
4 3 2 1 2 3
5 4 3 2 1 2
6 5 4 3 2 1