4.4- Spirocyclohexa-2,5-dienones

Likewise, the oxidation of phenolic enaminone derivatives 22 with [bis(triflu-oroacetoxy)iodo]benzene under mild conditions leads to spirocyclohexa-dienone 23 (Scheme 10) [25]. 

Treatment of symmetrically substituted bis(arylmethylthio)alkynes with either IC1 or Br2 and in the strict absence of water promotes cyclization to 1//-2-benzothiopyrans (Scheme 129). Initial formation of a cyclic halonium species induces the electrophilic ring closure. In the presence of nucleophiles, ipso attack is favored and a spirocyclohexa-dienone results. The alkynes are accessible from arylmethyl thiocyanates and sodium acetylide <1998JOC4626, 2003EJ047>. 

The analogous oxidation of phenolic enaminone derivatives 255 has been used to prepare spirocyclohexa-dienones 256 (Scheme 3.105) [324]. 

Talapatra B, Chaudhuri P K, Talapatra S K 1982 (-)-Maglifloenone, a novel spirocyclohexa-dienone neolignan and other constituents from Magnolia liliflora. Phytochemistry 21 747-750... 

In a related study, Yu and co-workers had also selected the use of BTI over that of DIB to convert 4-hydroxyphenyl Af-phenylbenzamides such as 127a into oxindolic spirocyclohexa-2,5-dienones such as 128a (Fig. 32) [89]. These authors... 

Fig, 30 Zhang s synthesis of p-lactamic and pyrrolidonic spirocyclohexa-2,5-dienones... 

Fig. 38 Fujioka-Kita s synthesis of lactonic spirocyclohexa-2,5-dienones from l-(4-hydroxyaryl) cyclobutanols...

Meerwein transpositions performed by Canesi and co-workers under quasiidentical reaction conditions [100]. However, the presence of water caused the opening of the cyclopentanone unit of 153 with rearomatization of the phenolic moiety. The resulting phenolic carboxylic acids 154 were then oxo-spirocyclized with a second equivalent of DIB to furnish the lactonic spirocyclohexa-2,5-dienones 155 [99] (Fig. 38). 

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