A proposal for the synthesis of cortistatin A

The  proposal is as following:

The discussion of key steps:

1. the c-h insertion to form the five-membered ring is well known.

2. The oxygen bridge can then be formed through epoxidation and epoxide ring expantion which might be the biological way also.

3. alternatively the oxygen bridge can be formed by the diazo insertion into C=O and then 3+2 addition.

4.the 7-membered quadene can be constructed by carbene/carbenoid inerstion into aromatic rings followed by elimination of OAc.