Process for the preparation of efinaconazole
The present invention relates to a process for the preparation of Efinaconazole and salts thereof.
1. A process for the preparation of (2R,3R)-2-(2,4-difluorophenyl)-3-(4-methylene piperidin-1-yl)-1-(1H-1,2,4-triazol-1-yl)butan-2-ol [efinaconazole], a compound of formula I,
the process comprising:
(a) reacting (2R,3S)-2-(2,4-difluorophenyl)-3-methyl-2-[(1H-1,2,4-triazol-1-yl)methyl]oxirane, a compound of formula II, with 4-methylenepiperidine, a compound of formula III or salt thereof, to obtain crude efinaconazole;
(b) reacting the crude efinaconazole obtained from step (a) with an optically active acid to obtain a reaction mixture containing an acid addition salt of (2R,3R)-2-(2,4-difluorophenyl)-3-(4-methylene piperidin-1-yl)-1-(1H-1,2,4-triazol-1-yl)butan-2-ol, wherein the optically active acid is di-p-toluoyl tartaric acid;
(c) separating the acid addition salt of (2R,3R)-2-(2,4-difluorophenyl)-3-(4-methylene piperidin-1-yl)-1-(1H-1,2,4-triazol-1-yl)butan-2-ol from the reaction mixture; and
(d) converting the acid addition salt of ((2R,3R)-2-(2,4-difluorophenyl)-3-(4-methylene piperidin-1-yl)-1-(1H-1,2,4-triazol-1-yl)butan-2-ol) to (2R,3R)-2-(2,4-difluorophenyl)-3-(4-methylene piperidin-1-yl)-1-(1H-1,2,4-triazol-1-yl)butan-2-ol.
2. The process as claimed in claim 1 , wherein a content of a (2S,3S) isomer of efinaconazole, a compound of formula IV, and/or a (2R,3 S) isomer of efinaconazole, a compound of formula V, and/or a (2S,3R) isomer of efinaconazole, a compound of formula VI
is less than 0.5% w/w with respect to efinaconazole as determined by HPLC.
3. The process as claimed in claim 1 , wherein the step (a) is carried out in presence of a Lewis acid.
4. The process as claimed in claim 1 , wherein the step (a) is carried out in presence of a solvent.
5. The process as claimed in claim 1 , wherein the step (a) is carried out in presence of a phase transfer catalyst.
6. The process as claimed in claim 1 , wherein the step (a) is carried out in presence of a Lewis acid selected from the group consisting of lithium bromide, boron trifluoride etherate, zinc chloride, ferric chloride, aluminium chloride, lithium perchlorate and stannic chloride, copper(II) trifluoromethanesulfonate, zinc acetate, and zinc trifluoromethanesulfonate.
7. The process as claimed in claim 1 , wherein the (2R,3R)-2-(2,4-difluorophenyl)-3-(4-methylene piperidin-1-yl)-1-(1H-1,2,4-triazol-1-yl) butan-2-ol, the compound of formula I,
is prepared by a process comprising the step of reacting (2R,3S)-2-(2,4-difluorophenyl)-3-methyl-2-[(1H-1,2,4-triazol-1-yl) methyl] oxirane, a compound of formula II, with 4-methylenepiperidine, a compound of formula III or salt thereof, in the presence of a Lewis acid.