Azo bridges from azines .20. Parallel cyanovinylene and azo groups - Synthesis and chemistry

Introduction of a cyano group into the olefinic bridge of 10 (type A) leads to the formation of 16 (type C) in high yield. To obtain 16 first 10 is transformed into isoxazoline 11 which is opened to hydroxy nitrile 12 (type B) from which after brosylation (15) 16 is isolated. Reduction of the azo bridge in 15 affords half cage 13. Smooth oxidation of 12 yields oxo nitrile 19, from which under basic conditions another half cage (18) results. Unexpectedly, on heating with triethylamine 19 undergoes complete rearrangement of the bridges, 21 being formed on release of strain. The course of this reaction which has to pass through a cage with a diazetidine moiety is discussed.