Quinuclidone
Quinuclidones are a class of bicyclic organic compounds with chemical formula C7H11NO with two structural isomers for the base skeleton 3-quinuclidone and 2-quinuclidone.
3-Quinuclidone (1-azabicyclo[2.2.2]octan-3-one) is an uneventful molecule that can be synthesized as the hydrochloric acid salt in a Dieckman condensation:
Organic reduction of this compound gives the compound quinuclidine, structurally related to DABCO, which has one additional bridgehead nitrogen atom.
The other isomer, 2-quinuclidone, appears equally uneventful, but in fact it has defied synthesis until 2006. The reason is that this molecule is very unstable because its amide group has the amine lone pair and the carbonyl group not properly aligned, as may be expected for an amide, as a result of steric strain. This behaviour is predicted by Bredt's Rule, and formal amide group resembles in fact an amine, as evidenced by the ease of salt formation.
The organic synthesis of the tetrafluoroborate salt of 2-quinuclidone is a six-step affair starting from norcamphor the final step being an azide - ketone Schmidt reaction (38% yield):
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