The Ritter reaction of 4-hydroxyadamantan-2-one (with acetonitrile in the presence of boron trifluoride-ether complex and trifluoroacetic acid) takes an unusual path and yields diastereoisomeric 9-methyl-1-(4-oxo-2-adamantyloxy)-8-oxa-10-azatetracyclo[5.3.1 12,6 .1 4,11 ]tridec-9-enes as the major products. Their structure was established by X-ray analysis.