Thiocarbamylation, catalysis

Difficulty finding conditions that would allow both efficient sequencing and suppression of the O-to-N shift led us to investigate tertiary amine catalysis of thiocarbamylation. Complete reaction of ONCS showed little effect of solvent on coupling. Adding 1.5 to 2.5 equivalents of acetic acid, however, decreased the fraction of the desired product (Table HI). 

Table III. Tertiary-amine catalysis of thiocarbamylation with ONCS...

Various amines were tested near neutrality for thiocarbamylation catalysis (Table IV). Amine pKa varied directly with reaction rate, and inversely with the percentage of correct product. Rapid reaction in the absence of tertiary amine suggested another activation pathway for thiocarbamylation. 

That coupling could be catalyzed without tertiary amines led to examination of non-tertiary amine catalysis of thiocarbamylation. Tests with sodium salts revealed a moderate catalysis by acetate, and weaker effect of formate (data... 

---