Preparation of SEMCl

SEMCl (2-trimethylsilylethyoxymethyl chloride)
expensive, 25ml $500
so just make it!

st: 2-TMS ethanol 1.o eq. (100 g, $500)
paraformaldehyde 1.1eq.
neat.
control temperature below 20C by ice bath.
Bubble HCl gas through the mixture. exothermic. HCl flow rate need to be controlled so that the INSIDE temp below 20C.
after a while, about 10-20 min, the solution became two layers and both are clear. then stop HCl gas.
separate the top layer. dilute the top layer with pentane and dried it over mgso4 at 0 C for 1 hr.
then concentrated below rt.
what you have now is pure semcl! ready to use. H-NMR showed only pure compound.

stored over CaCl2 in freezer.

deprotection of benzyl on an amine

1. pd/c, hydrogenation.
known to be slow compare to benzyl ether.
acidic solvents like HCl/MeOH or AcOH was reported to give good results.

2. CAN/MeCN/water
mild condition, but works only for tertiary amine.

3. substitute the benzyl group with a carbamate, then remove the carbamate by various ways.
ex. vinyl formate ,allyl formate, trichloro ethyl formate,

4. oxidize it to benzoyl, then hydrolysis.

an interesting reaction- a new finding

the above rxn is a total failure. No product isolated. only st remained after 12 hr.
Seems the alpha-oxygen played some rule in this coupling rxn.

KHMDS is nucleophilic ??

In this rxn, the base KHMDS removed the benzoyl group! at -20C.
I guess the bulky silane attacked the ester and the alcohol was freed.
so the conclusion is KHMDS is quite nucleophilic.

An interesting reaction

The above reaction just won't go on my hand despite excess base.
But, the following rxn is so quick that the rxn is done within 10 min at rt.