Sulfur acyl isothiocyanates

Dihydro-1,3-oxazines (398) are cyclic intermediates in the synthesis of a-amino-y-oxo acid esters by reaction of acyliminoacetates with enamines derived from six-membered ketones . Sulfur-containing heterocycloadducts 399 and 400 have been prepared by [4 -I- 2] cycloaddition of enamines to heterocumulenes like thioacyl isocyanates and acyl isothiocyanates . 

Acylations of triazolinethiones by acyl halides, isocyanate or isothiocyanate under mild conditions take place on sulfur, but higher temperatures appear to favour Af-acylation as in Scheme 31 (74kgs8Si). 

Addition reactions of 2-chloro-3-pyridylcarbonyl isothiocyanate with primary amines yield acylated thioureas 1. Because of the ambident character of the thiocarbamoyl group, in the following cyclization step the 2-chloro substituent of the pyridine may react either with the sulfur or the nitrogen center, depending on the reaction conditions. In the example below, heating under reflux in toluene yields 2-aminopyrido[3,2-e][l,3]thiazin-4-ones, whereas the anion prepared by metalation with lithium hydride in dimethylformamide at room temperature leads to 2-thioxo-l,2-dihydropyrido[2,3-c/]pyrimidin-4(3//)-ones 2.6... 

---