Diastereoselectivity in the Overman rearrangement of O-cyclohexylideneethylimidates

Conformationally biased cyclohexylideneethanols were prepared and converted to trichloroacetimidates, which then were subjected to the thermal Overman rearrangement. The rearrangement of axially unshielded imidates was unselective, providing isomeric amides in equal ratio. The axial face shielding in the 3,3,5-trimethylcyclohexylidene system resulted in highly selective nitrogen attack from the equatorial side.