title: A mechanistic study on the Hooker oxidation: synthesis of novel indane carboxylic acid derivatives from lapachol.
abstract: The Hooker oxidation is one of the most intriguing transformations wherein lapachol (1) is readily converted to norlapachol (2) in very good yield. This one-pot reaction involves a very intricate mechanism in which the alkyl side chain of lapachol is shortened by one carbon unit. Previous studies have unequivocally established the involvement of an indane carboxylic acid derivative 3, as a key intermediate (Hooker intermediate), and its simultaneous conversion to norlapachol (2) via the oxidative cleavage of vicinol diol and subsequent intramolecular aldol reaction of the resulting keto acid. However, the formation of the key Hooker intermediate 3 from lapachol (1) remains ambiguous. The present study has thrown some light on the formation of the key intermediate 3 from lapachol (1) via benzilic acid rearrangement of the corresponding labile o-diquinone intermediate 8 derived from lapachol. The involvement of o-diquinone intermediate 8 in the Hooker oxidation has been further established by trapping of this labile intermediate as the corresponding phenazine derivative 9. The involvement of benzilic acid rearrangement as a key step in the Hooker oxidation is further shown with a variety of o-quinones prepared from lapachol (1).
authors.affiliation: Department of Chemistry, Indian Institute of Technology Madras, Chennai, 600036, India.
authors.forename: Kenneth O
authors.initials: KO
authors.lastname: Eyong
authors.forename: Manohar
authors.initials: M
authors.lastname: Puppala
authors.forename: Ponminor Senthil
authors.initials: PS
authors.lastname: Kumar
authors.forename: Marc
authors.initials: M
authors.lastname: Lamshöft
authors.forename: Gabriel N
authors.initials: GN
authors.lastname: Folefoc
authors.forename: Michael
authors.initials: M
authors.lastname: Spiteller
authors.forename: Sundarababu
authors.initials: S
authors.lastname: Baskaran
mesh_terms: D002264:Carboxylic Acids / Q000138:chemical synthesis* / Q000737:chemistry; D007189:Indans / Q000138:chemical synthesis* / Q000737:chemistry; D008958:Models, Molecular; D015394:Molecular Structure; D009285:Naphthoquinones / Q000737:chemistry*; D010084:Oxidation-Reduction
chemical_list: D002264:Carboxylic Acids; D007189:Indans; D009285:Naphthoquinones; C008252:lapachol