Naturalproductman’s Blog

Hey, is that a natural product?!

6 to 5 Ring Contraction

Posted by naturalproductman on July 5, 2010

Changing a steroid ring from the classical 6,6,6,5-carbon skeleton to a 6,6,5,6-carbon tetracycle can be a challenge, however, it appears to happen in nature with natural products such as cyclopamine and nakiterpiosin.  Athanassios Giannis and co-workers at the Universitat Leipzig in Germany have recently reported in JACS on a way to do such a transformation by using an 11-hydroxy steroid (hydroxy group in only the C-ring adjacent to the axial chiral methyl group)  and subjected to Comin’s reagent (2-[N,N-bis(trifluoromethanesulfonyl)amino]-5-chloropyridine), which is just a triflating agent, and DMAP in toluene under heated conditions to yield the 6 to 5 ring contraction product.

rearrangement

JACS paper

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