Novel polycyclic heterocycles. VII. Synthesis of tetracyclic ketones and derivatives from tricyclic 5,11‐dihydrodibenz[b,e][1,4] oxazepines

Abstract

AbstractMichael addition of 5,11‐dihydrodibenz[b,e][1,4]oxazepines to acrylonitrile gave 5,11‐di‐hydrodibenz[b,e][1,4]oxazepine‐5‐propionitriles, which were converted to the corresponding methyl 5‐propionates. Mild alkaline hydrolysis of these esters furnished the key intermediates, the 5,11‐dihydrodibenz[b,e] [1,4]oxazepine‐5‐propionic acids. In the preferred procedure, these propionic acids were cyclized to the tetracyclic ketones in yields of 60‐90%, by the action of one equivalent of trifluoroacetic anhydride in benzene. When ring C was involved in cylcization, 1,2‐dihydro‐3H,7H‐quino[8,1‐cd][1,5]benzoxazepin‐3‐ones were obtained, and when ring A was involved, 1,2‐dihydro‐3H,8H‐quino[1,8‐ab] [4,1]benzoxazepin‐3‐ones were formed. With 1c, both modes of cyclization were observed. In an alternative procedure that gave lower yields, the propionic acids were first converted to the corresponding acid chlorides, and these were cyclized by means of anhydrous stannic chloride; as anticipated, the products by this method were identical with those obtained via the trifluoroacetic anhydride method. Several reactions of these tetra‐cylcic ketones, e.g., their ease of oxime formation, and dehydrogenation to the α,β‐unsaturated ketones, are described. The α,β‐unsaturated ketones do not form oximes.The structures assigned to the ketones are based on interpretations of their pmr, uv, and ir spectra. These assignments were confirmed by an X‐ray analysis of a single crystal of one representative ketone, 2b; the X‐ray study was also useful in indicating the thermodynamically preferred conformation of 2b. The structures of all the other compounds followed from similar spectral interpretations. The mass spectra of a few compounds are also discussed.