Organic Chemistry
To add (for step v) and remove (for step i) the protecting group to produce the desired product.
To add (for step v) the protecting group and remove (for step i) the chromic group to produce the desired product.
To add (for step i) and remove (for step v) the protecting group to produce the desired product.
To add (for step i) and remove (for step v) the preventing group to produce the desired reagent.