Mordechai Pasternak

Photochemical studies: Irradiation induced transformations of reversibly dissociating cyclopentadienone-dimers and their monomers

Abstract Irradiation of dissociating cyclopentadienone-dimers ( 2 b, c, e ) results in formation of two types of cage-products ( 5 and 8 ) in very low quantum yields and good, but wavelength and phase dependent chemical yields. Both processes are intramolecular, for 2b this was shown using isotopic labeling and massspectrometric techniques. Sensitization and quenching experiments indicate that triplet states are involved The mechanistic pathways are discussed. The cyclopentadienones( 1 b,c,e ) were isolated for the first time and irradiation of 1b in the solid gave exclusively the symmetric cage ( 8b )

The dimer of 2,3-dimethyl-3,4-(o,o′-biphenylene)cyclopentadienone: thermal and photochemical transformations

The title compound (1) undergoes a degenerate Cope rearrangement which was studied within the n.m.r. time scale; further thermal and photochemical transformations of (1) are also presented.

Isolation, spectral properties, and photochemistry of unstable substituted cyclopentadienones

A new approach to the isolation of unstable cyclopentadienones from dissociating dimers is described; 2,5-dimethyl-3,4-diphenylcyclopentadienone (1d) and two other derivatives, (1e) and (1f), were obtained in crystalline state and their spectral properties were investigated, and irradiation of (1d) in the crystal quantitatively gave the cage-product (3).