Photochemie von Aminoketonen, 14. Synthese und transannulare Photocyclisierung von 2‐Benzoyl‐1,4‐bis(tosyl)piperazinen

Abstract

Photochemistry of Amino Ketones, 14 1) . – Synthesis and Transannular Photocyclisation of 2‐Benzoyl‐1,4‐bis‐(tosyl)piperazines 1,1‐Dialkyl‐1,2‐bis(tosylamino)ethanes 4 are prepared in a three‐step reaction starting with dialkyl ketones 1 . With strong bases in dimethylformamide compounds 4 react regioselectively with 1,2‐dibromoalkyl phenyl ketones 5 to afford the 2‐benzoyl‐1,4‐bis(tosyl)piperazines 6 . On irradiation (≥ 300 nm) the piperazines 6a , b , f , g , without substituents in position 6, undergo Norrish‐II cleavage yielding open‐chain products. Depending on the ring conformations the 2,2‐dialkylpiperazines 6c , d , e form diazabicycloalkanes 10 and 11 on irradiation.