12 years, actually, and that's with two of the best research groups of the day (Woodward & Eschenmoser) working in collaboration.
I don't even want to count the steps. Suffice it to say that there are a lot.
Vitamin B12 is a lot bigger than Norzoanthamine, however. They are two very different molecules. The B12 synthesis was completed in 1973 too, which was well before a lot of the modern catalytic synthetic methodology was well developed.
If you want to read all the stuff on B12, check out "Classics in Total Synthesis" by Nicolau and Sorensen, VCH (1996), pp. 99-136. That has all the references to the original journal articles too.