Methods of synthesizing thyroid hormone analogs and polymorphs thereof

A process comprising:

• (a) contacting R1MgX or R1Li with a compound of Formula (I):
• (I) to form a compound of Formula (II):
• (II), in which R1 is isopropyl or isopropenyl, X is halo and R2 is H or an amine protecting group;
• (b) converting the compound of Formula (II) to a compound of Formula (III):
• (III) in the presence of a base when R1 is isopropenyl or in the presence of an oxidizing agent when R2 is isopropyl;
• (c) when present, removing the amine protecting group R2 of the compound of Formula (III) to form 6-(4-amino-2,6-dichlorophenoxy)-4-isopropylpyridazin-3(2H)-one;
• (d) converting 6-(4-amino-2,6-dichlorophenoxy)-4-isopropylpyridazin-3(2H)-one to 2-(3,5-dichloro-4-((5-isopropyl-6-oxo-1,6-dihydropyridazin-3-yl)oxy)phenyl)-3,5-di oxo-2,3,4,5-tetrahydro-1,2,4-triazine-6-carbonitrile (“Compound A”);
• and
• (e) forming a morphic form of Compound A (Form I) characterized by an X-ray powder diffraction pattern that includes peaks at about 10.5, 18.7, 22.9, 23.6, and 24.7 degrees 2θ.