Thursday, November 15, 2007

benzyl ether protection group


1.NaH, THF/DMF, BnBr.
TBAI can be used, more active BnI is formed.

2. CsOH/M.S./DMF or Cs2CO3/ DMF or DMSO, BnBr
Cs is a good base, works for very unreactive alcohol.

3. TfOH, DCM, hexane, benzyl trichloroacetimidate
acidic conditon, works for base-sensitive substrate. generally, low yield.

4. Ag2O, BnBr, solvent,( in darkness)
good selectivity between primary and secondary alcohols. very mild condition.

5. bis(butyl)tin oxide/CsF/BnBr
works for monoprotection of 1,2-diol.

6. Cu(acac)2/BnCl/reflux
only protect primary alcohols.

very mild condition. tolerates many functional groups.

8. benzyl chloride/Bu4NBr/NaOH aquous/

1. 5% Pd/c, in THF the reation is faster than MeOH.
addition of base (TEA, pyridine) can prevent benzylether from hydrogenation conditions.(H2, 1 atm, Pd/C, 5%, MeOH).
Removal of trityl ether is slower than hydrogenation of double bond. So short time (1-2hr) hydrogenation won't touch trityl group, of course, base can also be used to pretect trityl group.
removal of benzylether is 20 times quicker in THF than in MeOH(Pd/C, 1atm H2, rt).

2. O3 can oxidize Bn to Benzylester.
3. RuO2/NaIO4 oxidation can oxidize Bn to Benzyl ester.
4. DDQ.
with or without water.
UV/MeCN. (mild condition, can tolerate double bonds).
5. dissolving metal.
Na/Li in liquid ammonia.

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