No abstract

No abstract

Terminal alienes linked to cyclohexenones by hydrocarbon chains were synthesized and irradiated with UV light. It was found that [2 + 2] cycloaddition occurs regiospecifically in high yield. The adducts were oxidized by ozone to 1,3-diketones which underwent cleavage to the corresponding keto acids.Photochemical intramolecular addition of 1,2-propadiene (aliene) to cycloalkenones has been studied1 and has been shown to be an effective tool in organic synthesis.1

Substituted alienes linked to cyclohexenones by hydrocarbon chains 1-5 were synthesized and irradiated with UV light. The product structures were determined, and the mechanism of the [2 + 2] cycloaddition is discussed. The possibility of using chiral aliene as a template for the synthesis of chiral spiro systems is described.

The [2 + 21 intramolecular photocycloaddition of E and Z olefins to a cyclohexenone has been investigated; it is concluded that the bond to C(3) in the cyclohexenone is formed first to give the diradical intermediates (7a) and (7b).Inter-and intra-[2 + 21 photocycloaddition of unsaturated bonds to enones is an efficient reaction well established in organic synthesis1 despite the fact that the mechanism is not yet fully known. It is assumed that 1,4-diradicals are intermediates, but to date it has not been determined whether the bond to C(2) or C(3) of the enone system is formed first.2 The assumption that the first bond is formed to C(3) was made recently in order to explain some experimental result^.^ We now describe results of an intramolecular [2 + 21 photocycloaddition of E and Z olefins to a cyclohexenone which are consistent with a mechanism where the first bond is formed to C(3).Our approach was based on product analysis. If the photocycloaddition of the E isomer (1) occurs either via a concerted