beta-Oxonitriles (1) are easily condensed with cyclic ketones (2a-e) i
n anhydrous strong acidic conditions to give 1-oxa-5-azaspiro[5.5]unde
c-2-en-4-ones (3a-e). In the same manner acyclic ketones (2f,g) or ald
ehydes (2h,i) afford 2,3-dihydro-4H-1,3-oxazin-4-ones (3f-i). The mech
anism of this cyclocondensation is discussed.