Sulfur a and nitrogen in this small mlecule aren't indipendent in the attempt to protect the sulfur you will block the nitrogen too

See also strusctures here ...

http://www.ias.ac.in/chemsci/Pdf-Jan2008/143.pdf

Thiols are MOM-protected using bromochloromethane and methanol under phase-transfer catalysis with benzyltriethylammonium chloride. Under this condition alcs. and carboxylic acids are recovered unchanged as reported earlier

---A simple method for the selective MOM protectionof thiols, Toste, F. Dean; Still, Ian W. J., Synlett (1995), (2), 159-60.

You may apply this condition too and see what happen

Good luck

Sorry gentlement I do not probably understand completely what your answers refers to The Methimidazole molecule Fariba refers as to willinf to S protect, indeed isn't a thiol properly speaking, it may behave as a thiol but it isn't a thiol (1-methyl-1,3-dihydro-2H-imidazole-2-thione). For sure it would have a partial character of the tautomeric thiiolic form but to the expenses of the conjugated nitrogen which will loose its proton, that it is what I meant on the first answer.

If is that what Fariba wants then you all righ there are a lot of procedures that can be used ...

Regards

Hi Fariba,

numerous examples of MOM-protection (selective to S- vs N-atom) is described in Bull. Korean Chem. Soc. 2003, Vol. 24, No. 11 , pp.1689-1691 - methimazole is also included.

As catalyst, authors use low-valent Ti, but I am sure that ordinary P2O5 will work perfect in combination with dimethoxymethane CH3OCH2OCH3 too ( Org. Synth. Coll., 9, 539 (1998) - via inet available from www.orgsyn.org ).

However, two problems will still present - selective alkylation and deprotection.

Andrei Rogoza

Hi,

The method you have suggested here does it work with aromatic thiols? Or is it only for heterocyclic thiols?

Parthasarathi Das

Examples are given for both electron-rich and electron-deficient heterocycles, so arylthiols are also sould be covered by such method