Here, we have demonstrated that the presence of a carbonyl group at C7 position prevents
the olefin metathesis of endo-norbornene derivatives due to complexation of the metal alkylidene. Time-dependent
NMR studies showed the presence of new proton signals in the metal alkylidene region,
which indicate the formation of metal complex with the carbonyl group of the substrate.
These observations were further proved by ESI-MS analysis. Whereas computational studies
showed that the catalyst was interacting with the C7 carbonyl group and aligned perpendicular
to that of norbornene olefin. These endo-keto norbornene derivatives were reduced to hydroxyl derivatives diastereoselectively.
Ring-rearrangement metathesis (RRM) of these hydroxyl derivatives, produced the [6/5/6],
and [5/6/5] carbo-tricyclic cores of natural products in one step. Whereas the RRM
of O-allyl derivatives, delivered the oxa-tricyclic compounds in a single step with excellent
yields.
Key words
Grubbs catalyst - 7-hydroxynorbornene - 7-ketonorbornene - olefin metathesis - natural
product synthesis
