Chlonns, synthesis

In a later version of the synthesis [9], the trifluoroethyl difluoromethyl ether is made directly from tnfluoroethanol and chlorodifluoromethane (equation 2) and then chlorinated to give the final product. Again, the major problem is overchlorination, because all the hydrogens are readily replaced by chlonne. Separation of the overchlonnated by-products poses a special problem because of close boiling points. This problem can be solved by adding acetone to create a more easily separable azeotrope of acetone and isoflurane [10]. 

Deoxygenation of a nitrone. Some years ago Todd and co-workers noted that 1-pyrroline-1-oxides can be obtained by reductive cyclization of a y-nitro ketone. This reaction was used recently in a synthesis of chlonns related to vitamin B,. Thus the nitro ketone 1 on reduction with zinc and acetic acid gives the pyrroline N-oxide 2 in high yield. The N-oxide is stable to triphenylphosphiue or trimethyl phosphite, but is reduced to the imine 3 in high yield by TiCl,. 

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