Azacarbocyclic spirodienones

A similar oxidation of the phenol derivatives 20 bearing aminoquinones at the ortho positions affords the respective azacarbocyclic spirodienones 21 (Scheme 9) [23]. 

Synthetic application of the oxidative dearomatization of ort/io-substituted phenolic substrates in the intramolecular mode is exemplified by the preparation of azacarbocyclic spirodienones 274 from phenol derivatives 273 (Scheme 3.114) [322]. 

For example, a variety of natural products bearing spirocyclic systems exist, and many of them are biosynthetically formed by oxidative spiroannulation processes. Hypervalent iodine(III) reagents are thus considered as one of the most effective oxidants for these oxidation processes. Several efficient methods for PIFA-induced spiroannulation reactions of phenols [48, 49] towards the total synthesis of discorhabdin alkaloids [50, 51] and their oxa-analogues have been published [52, 53], which were accomplished via hypervalent iodine oxidation of phenols or (9-trimethylsilylated phenol derivatives to the azacarbocyclic spirodienones as a key step (Scheme 8). 

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