Potassium Carbonate → Methyl(2Z)-2-bromo-4-[N-(tert-butoxycarbonyl)amino]-5-methylhexenoate

Participants

Reaction Conditions

Reaction Steps

N-Bromosuccinimide (4.60 g, 25.9 mmol) and anhydrous potassium carbonate (8.10 g, 58.8 mmol) are successively added, over a period of 20 minutes, to a solution of (methoxycarbonylmethylene)triphenylphosphorane (PH3P═CH—CO2Me, 7.90 g, 23.5 mmol) in dichloromethane (60 ml) cooled to −20.0° C. The mixture, yellow-brown, is left under stirring for 20 min and freshly prepared N-(Boc)Valinal 2 (4.74 g, 23.5 mmol) dissolved in CH2Cl2 (20 ml) is instilled. The addition completed, the mixture is left for 30 min at −20.0° C. and for 1 h at ambient temperature. A TLC check indicates the total disappearance of the aldehyde. The mixture is filtered on a fritted disc coated with celite, and the fritted disc is rinsed with ether. After evaporation of the filtrate under a vacuum, the yellow oil obtained is chromatographed on a silica gel (elution gradient Heptane/AcOEt 90/10→75/25). 2.10 g (27%, Rf=0.46 (AcOEt/Hept 1/3)) of pure isomer E, 0.63 g of mixture (7%, Z+E) and 3.2 g (41%, Rf=0.35 (AcOEt/Hept 1/3)) of pure isomer Z are obtained.

Provenance & Evidence