Org Prep Daily

September 28, 2006

CbzNH-lactone

Filed under: procedures — milkshake @ 12:03 am

 

The aminoacetonide 2.87g (Acros, 10.5 mmol) and triethylamie 2.5mL (18 mmol) was dissolved in dichloromethane 20mL and Cbz-OSu 2.617g (10.5 mmol) was added in one portion with cooling on ambient bath (exothermic). The mixture was stirred for 1 hour, then portioned between ethyl acetate 150mL and sat. bicarbonate 100mL. The organic phase was washed with additional sodium bicarbonate (100mL) and aqueous phases re-extracted with ethyl acetate (150mL). Combined organic extracts dried (MgSO4) and evaporated. The residue was dried on highvac. The obtained crude Cbz-protected acetonide ester (4.38g) was dissolved in dichloromethane 15mL, TFA 10mL was added, the mixture was stirred for 40 min then evaporated and dried on higvac. The residue was purified on a column of silica (150g) in a mix dichloromethane-ethyl acetate 1:2 (2 parts of EtOAc:1 part DCM, 4L total). Y=1.875g (61%) of a white crystalline solid.

1H(d6-DMSO, 400MHz): 7.343(m, 5H), 5.204(br s, 1H), 5.003(s, 2H), 4.615(m, 1H), 4.097(br s, 1H), 3.117(m, 2H), 2.623(ddAB, 17.3Hz, 12.6Hz, 1H), 2.368(m, 1H), 1.766-1.663(m, 4H)

3 Comments »

  1. is the final structure wrong? an OH seems to have gone for a walk, giving a delta lactone instead of a gamma lactone. or have i missed something subtle

    Comment by kiwi — September 28, 2006 @ 3:00 am

  2. There is no gamma O there anywhere, dude. Only beta and delta.
    The yield was slightly sucky because these hydroxylactones open up very easily – and I think it is happenning on the silica to some degree. Guess I should have silylated the OH before purification, that would supress it

    Comment by milkshake — September 28, 2006 @ 3:11 am

  3. ahh comment was at the end of a long day at the lab, i don’t know what i was thinking, but it sure looks stupid now.

    Comment by kiwi — September 28, 2006 @ 5:02 am


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