Documentation of a rare example of an intramolecular 1,2-addition of a trialkylborane to a carbonyl group

In the course of synthetic studies aimed at the elaboration of highly funtionalized ketone 1, we observed what appeared to be an extremely rare example of the addition of a trialkylborane to a carbonyl group. We were able to confirm the initial spectroscopic structural assignment by X-ray crystallography. Some preliminary mechanistic experiments suggest that the addition occurs directly in the absence of oxygen prior to oxidation of the trialkylborane during workup.