Dibromomethane-Zinc-Titanium(IV) Chloride

Enzyme-Assisted Enantioselective Synthesis of Natural (−)-β-Necrodol and Its Enantiomer

“…Several Ti-based methylenation procedures have been developed that avoid most of the problems encountered with Wittig-type processes . In our case, the keto group of (+)- 2 was methylenated, without any epimerization, by a zinc−dibromomethane−titanium(IV) chloride mixed reagent in THF to give (−)- 6 in 88% yield. Finally, LiAlH 4 reduction of (−)- 6 in Et 2 O at room temperature furnished the natural (−)-(1 R ,3 R )- β -necrodol, (−)- 1 in 98% yield and >98% ee.…”

Enantio- and Periselective Nitroalkene Diels-Alder Reactions Catalyzed by Helical-Chiral Hydrogen Bond Donor Catalysts

“…Unfortunately, the methylenation of diketone 15 by this protocol resulted in no desired product (Table 3, entry 1), presumably because it is sterically congested. We then directed our search to titanium-based alkenating reagents, being non-basic, they have found broad utility for various ketones [42]. Lombardo’s reagent [43,44], which is generated by aging the reaction mixture of CH 2 Br 2 , Zn and TiCl 4 at 5 °C for 3 days, has been successfully employed for enolizable ketones [45,46].…”