3‐Azabicyclische Ketone durch Reaktionen von 1,3‐Diethoxy‐2‐azapropenylium‐Salzen mit Enaminen cyclischer Ketone

Abstract

3‐Azabicyclic Ketones from 1,3‐Dialkoxy‐2‐azapropenylium Salts and Enamines of Cyclic Ketones1,3‐Diethoxy‐2‐azapropenylium salts 1 are powerful biselectrophiles and react diastereoselectively with enamines of five‐membered ring ketones 2 to yield novel 3‐azabicyclo[3.2.1]oct‐2‐en‐8‐one 5 after hydrolysis of the intermediate iminium salts 3, 4. Some of the iminium salts 3 can be hydrolyzed further to provide the diketo imines 6. With enamines of six‐membered ring ketones 7 the 3‐azabicyclo[3.3.1]non‐2‐en‐9‐ones 10, 11 are obtained after hydrolytic workup. Mixtures of diastereomers 10/11 are found in the case of 7a, b, whereas with 7g — j the endo‐phenyl derivatives 10 are formed exclusively. With the unsymmetrical enamine 7b only one regioisomer is observed. The decalone enamine 12 reacts with 1a to yield the tricyclic iminium salt 13. — The configuration of the bicyclic products has been determined by using NMR spectroscopic techniques (COSY, polarisation transfer by long range couplings); an X‐;Ray analysis of compound 10a is used as basis for the NMR assignments. General rules for the determination of the stereochemistry of these azabicyclic systems by 1H‐NMR shift arguments are derived.