Phenol ring opening photochemical

Irradiation/sodium hydroxide Photochemical phenol ring opening... 

The photochemical ring opening of chrom-3-enes (29) has been shown to produce o-quinoneallides (30). These have been trapped as the phenols (31) and (32) by their in situ reduction with lithium aluminum hydride (67JPC4045). The reverse process, thermal electrocyclic ring closure of the allide, is a facile reaction and hence any synthesis of an o -quinoneallide is effectively a synthesis of a chrom-3-ene. Many chromene syntheses are considered to proceed through the intermediacy of a quinoneallide and all of these are... 

Wirz and his coworkers have developed a method for the study of the dienone (295)/ phenol equilibrium. The dienone (295) is obtained by irradiation of dione (296) which undergoes photochemical elimination of ketene. Ketene formation can be confirmed at low temperature but under these conditions very little of the dienone (295) is observed since it readily undergoes photochemical ring opening to ketene (297). ... 

The three-step synthesis of 75c from 76a and 77a is characterized by the lack of any need for onerous protecting-group manipulation. From the starting phenol comes a dienone, from that a dieneketene, from that a doubly unsaturated methyl ester. The C,C-bis-alkylated components 80a and rac-81a, formed in the introductory synthetic step, already contain the complete set of C-atoms needed for crocetin (75b), albeit still arranged differently constitutionally. In the second step, the photochemical ring opening takes place, af-... 

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