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A formal synthesis of the muscarinic M-1 receptor antagonist (-)-TAN1251A (
7) from L-tyrosine is described. Central to this venture has been the const
ruction of the 1-azaspiro[4.5]decane skeleton present in the natural produc
t by an N-methoxy-N-acylnitrenium ion-induced spirocyclization. The dienone
generated in this transformation, 10, was converted to (-)-TAN1251A via tr
icycle 9, an intermediate in Kawahara's recent synthesis of racemic 7.