Org Prep Daily

September 29, 2006


Filed under: procedures — milkshake @ 3:51 am

2,6-dichlorobenzaldehyde 10.50g (60 mmol) was dissolved in chloroform 30mL with heating. The solution was cooled to R.T. and 1,3-propanedithiol 6.30mL (63mmol) was added. With cooling on ambient water bath, TMSCl 23mL (180mmol) was added dropwise over 10 min period (exothermic, gas evolution) and the resulting heterogennous mixture was stirred under Drierite-filled tube (as a gas outlet) for 20 hours. Two small spoons of 4A activated mol sieves powder were added (to absorb the dropplets of aq. HCl) and stirred for additional 30 minutes. The reaction mixture was filtered through a Celite pad (washed with chloroform) and the filtrates were evaporated. The obtained solid residue (16g) was dissolved in refluxing cyclohexane 100mL, filtered while hot (the filter funnel was rinsed with hot cyclohexane) and the filtrates were set aside to crystallize overnight (14 hours). The crystallized product (1st crop: 13.445g) was filtered, washed with hexane and dried on highvac. Evaporating the supernatants and re-crystallizing the residue from cyclohexane 20mL provided second pure crop (1.841g). Combined Y=15.286g (96%) of a white crystalline solid.

1H(CDCl3, 400MHz): 7.307(m, 2H), 7.128(t, 8.2Hz, 1H), 6.069(s, 1H), 3.144(td, t:14,4Hz, d:2.3Hz, 2H), 2.947(dt, d:14.2Hz, t:3.5Hz, 2H), 2.170(m, 1H), 2.019(m, 1H)


  1. 4A activated mol sieves-How do you activate them (by keeping in oven at 100 oC for overnight?)

    Comment by pmgb — May 14, 2008 @ 2:38 am

  2. You can actually buy activated powdered 4A sieves from Aldrich, it is not expensive – but I am not sure if they would work for really sensitive application, the only other chemistry I did with them was Stoltz Wacker-like oxidative cyclization and they worked fine.

    I think the usual procedure is to dry them first in a common electric glassware drying oven at 140-200C and then finish up the drying on oil bath at 200C on highvac overnight.

    Comment by milkshake — May 14, 2008 @ 1:46 pm

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