The Nazarov Cyclisation

The Effect of Lewis Acids on the Cycloaddition of 3,3,6‐Trimethylcyclohex‐5‐ene‐1,2,4‐trione: Hydrogen Transfer versus Cycloaddition with Cyclopentadiene

“…This compelled the use of TiCl 4 , which has been used previously as a catalyst, to diminish the cycloaddition energy barrier in preference to the side products. At room temperature, a good yield (63 %) of 2 was found with a diastereomeric ratio (dr) of 2:1 (endo/exo).…”

“…Although these species affect many reactions (e.g., Friedel-Crafts, [3] Nazarov, [4] Meerwein-Pondorf-Verley, and Oppenauer reactions [5] ), the Diels-Alder cycloaddition [6] is the most widely recognized as benefitting from the addition of Lewis acids. [7] In a typical [π 4s +π 2s ] cycloaddition, the catalyst has been shown to lessen the energy dif- ference between the diene HOMO and dienophile LUMO energies through complexation to Lewis basic sites in the dienophile.…”

Synthesis of 7-Oxo-5-deoxystrigol, a 7-Oxygenated Strigolactone Analog

“…Dienone 6 was then subjected to Nazarov cyclization by treatment with H 3 PO 4 to give 7 (88%). 15) Notably, the H 2 SO 4 -mediated reaction suffered from a lack of reproducibility, and such other Brønsted/Lewis acids as FeCl 3 , phosphomolybdic acid, and P 2 O 5 -MsOH only led to decomposition of the substrate. The next step was the chemoselective reduction of a non-conjugated ketone in 7.…”

The chemistry of bisallenes

“…The oxidation of 24 with magnesium monoperoxyphthalate provides 209 in 32% isolated yield [138]. Looking at the structures of starting material and product 209 the process resembles the Nazarov cyclization of divinyl ketones to cyclopentenones [140]. …”