The next sequence of steps zips up squalene, using one double bond after another for nucleophilic attack on carbocation intermediates:

Finally, a miracle occurs; a series of rearrangements, culminating with loss of a proton, moves the methyl groups and hydrogens necessary to produce lanosterol:

You will find a problem in the problem set asking you to break down the miracle into a series of discrete steps.

We are leaving a lot undescribed here. Some things to think about:

• Can it be duplicated in the laboratory?

• Is it concerted? Or a series of steps?

• If series of steps, are the intermediates released and rebound?