N-methoxy-N-acylnitrenium ions: application to the formal synthesis of (-)-TAN1251A.

[structure: see text]. A formal synthesis of the muscarinic M(1) receptor antagonist (-)-TAN1251A (7) from L-tyrosine is described. Central to this venture has been the construction of the 1-azaspiro[4.5]decane skeleton present in the natural product by an N-methoxy-N-acylnitrenium ion-induced spirocyclization. The dienone generated in this transformation, 10, was converted to (-)-TAN1251A via tricycle 9, an intermediate in Kawahara's recent synthesis of racemic 7.