|It's like a crossword puzzle...|
Source: Chemistry World
Just one tiny problem: what the heck is that structure? Maybe the atoms were inadverently deleted in transit, or perhaps it's meant as an artistic statement? I can't imagine this molecular graphic falls under Elsevier copyright protection.
In a way, it's like a detective mystery: can you infer what's missing? I took a crack at it myself (see below). I figured the structure on the right was either a dithiane (S,S) or ketal (O,O). The bottom ring could have any combination of N,O,S, so we'll swap in a morpholine. The aromatic? Gotta be a pyridine. Uh-oh, there could be anything terminating those 'short' bonds on the cyclopentane, or on the alpha bonds stemming below the cyclopropane. I'll just infer methyl groups, for now.
Of course, without knowing the actual natural product, and without access to database software due to the holiday, I have no way to know if I'm barking up the right tree. Anyone care to help?
Happy Fourth of July, everyone!
Update, 7/4/12 - Commenter @azmanam wins the platinum coin for his search efforts, locating the correct intermediate from a Boger total synthesis (see below). So, in the end, I went 4 for 9 on "mystery atoms!"