Org Prep Daily

February 18, 2009

2-bromo-4-iodo-5-difluoromethylpyridine

Filed under: procedures — milkshake @ 9:45 pm

 

The aldehyde 800mg (2.565 mmol) slurry in dichloromethane (not anhydrous, 6mL) was placed on ambient water bath, Deoxyfluor 0.80mL (1.7 equiv.) was added in one portion and the mix was stirred under Ar for 150 min, then quenched by addition of few spoons of crushed ice.  The reaction mix was portioned between ether 120mL and water 120mL, separated and the aqueous phase was re-extracted with ether 120mL. The organic extracts were washed with aqueous sat. NaHCO3 120mL, combined, dried (MgSO4) and evaporated. The crude product was purified on a column of silica (40g) in hexane-dichloromethane 1:1 mix, isocratic. Y=672mg of pearl-shiny white soft flakes. (78.5% th)

1H(d6-DMSO, 400MHz): 8.464 (s, 1H), 8.386(s, 1H), 7.072 (t, 53.5Hz, 1H); 19F(d6-DMSO, 376.5Mhz): -115.74 (d, 53.7 Hz, 1F)

The starting aldehyde preparation was described here on July14 2008.

Note: This kind of reactions is often initiated by one drop of ethanol but here common-grade DCM serves equally well. Deoxyfluor is a more stable alternative of the popular DAST reagent –  and it is just as nasty (HF burns). Gloves, sash down,  larger-scale experiments should be quenched by pouring the mix on ice as the quench is very  exothermic.  The aqueous washings contain HF so one may want to use gloves during the work-up as well.

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