33698-69-0Relevant academic research and scientific papers
A new efficient route for multigram asymmetric synthesis of alkannin and shikonin
Couladouros, Elias A.,Strongilos, Alexandros T.,Papageorgiou, Vassilios P.,Plyta, Zoi F.
, p. 1795 - 1803 (2002)
A short and convergent approach for the synthesis of alkannin, shikonin and shikalkin is presented. A Hauser-type annulation of cyanophthalide 26 with enone 7 affords the complete aromatic system in just one step with concomitant attachment of the entire side chain. Subsequent Corey's oxazaborolidine mediated asymmetric reduction of the above advanced intermediate, leads to the required isomer in high enantiomeric excess. Finally, a selective and high yielding deprotection protocol furnishes the title compounds as pure crystalline precipitates. Thus, a multigram synthesis of shikonin, alkannin and shikalkin is achieved in high yield and enantioselectivity.
Photochemistry of 1,5-hexadien-3-ones: Wavelength-dependent selectivity in intramolecular enone-olefin photoadditions
Dauben, William G.,Cogen, Jeffrey M.,Ganzer, George A.,Behar, Victor
, p. 5817 - 5824 (2007/10/02)
The photochemistry of ten 1,5-hexadien-3-ones in methanol is studied over the wavelength range of 313-366 nm, by using monochromatic light. With the goal of understanding the unusual wavelength-dependent selectivity observed for 5-methyl-1,5-hexadien-3-one (1), quantum yield measurements, structure reactivity studies, triplet sensitization, and quenching experiments are performed. While six of the ten dienones studied show selectivities that are independent of irradiation wavelength from 313 to 366 nm, four of the dienones exhibit wavelength-dependent selectivities that are similar to that observed in 1, thus establishing that 1 is not unique, as previously believed. Triplet sensitization studies suggest that the wavelength dependence results, largely, from a single-state α-cleavage reaction that competes with triplet cycloaddition. A variety of triplet quenchers were ineffective at inhibiting these reactions. Some possible mechanisms are discussed.
