title: Photochemistry of arylidene-beta-ionones: a highly efficient route to novel tricyclic ketones through intramolecular, exoselective photochemical (4 + 2) cycloadditions, occurring only in an aqueous-organic solvent.
abstract: (E,E)-Arylidene-beta-ionones (1a-f) are converted to 1,7,7-trimethyl-3-(E-2'-arylethenyl)-2-oxabicyclo[4.4.0]deca-3,5-dienes (3a-f, approximately 90%) by irradiating in anhydrous solvents. Irradiation of (3a-f) in aqueous methanol results in Z,E-arylidene-beta-ionones (2), through retro-electrocyclization, which undergoes an intramolecular, exo-selective [4 + 2] photocycloaddition leading to 11-(exo)-aryl-1,7,7-trimethyl-tricyclo[4.4.0.1(2,4)]undec-5-ene-3-ones (8a-f, 60-80%). The latter rearrange over silica gel to afford, quantitatively, 5-aryl-7,11,11-trimethyl-tricyclo[5.4.0.0(3,6)]undec-1-ene-4-ones (5a-f). Irradiation of 1a-f in aqueous methanol leads to 8a-f, except in case of 1c,f wherein formation, respectively, of tricyclic ketones 9c (55%) and 9f (80%), derived from photodeconjugation in 2, followed by intramolecular [4 + 2] cycloaddition, is observed.
authors.affiliation: Department of Pharmaceutical Sciences, Guru Nanak Dev University, Amritsar 143005, Punjab, India. mpsishar@angelfire.com
authors.forename: Mohan Paul S
authors.initials: MP
authors.lastname: Ishar
authors.forename: Rajinder
authors.initials: R
authors.lastname: Singh
authors.forename: Kamal
authors.initials: K
authors.lastname: Kumar
authors.forename: Gurmit
authors.initials: G
authors.lastname: Singh
authors.forename: D
authors.initials: D
authors.lastname: Velmurugan
authors.forename: A Subbiah
authors.initials: AS
authors.lastname: Pandi
authors.forename: S S Sundra
authors.initials: SS
authors.lastname: Raj
authors.forename: H K
authors.initials: HK
authors.lastname: Fun