What is the correct order of these intermediates in the mechanism to add this protecting group? (1=the first intermediate ... 6=the last intermediate)
a) 1, 2, 3, 4, 5, 6
b) 6, 5, 4, 3, 2, 1
c) 3, 4, 5, 6, 1, 2
d) 2, 1, 6, 5, 4, 3