Abstract
1,4-Bis(trimethylsilyl)-1,4-dihydropyrazine (1), a very-electron-rich N-silyl-enamine with eight conjugated p electrons in the planar six-membered ring, exhibits different reactivity with respect to heterocumulenes X:C:Y (X, Y = O,S). Carbon dioxide is slowly inserted into one N-Si bond to give an electron-rich O-silylurethane functionality. Significant insertion into the second N-Si bond occurs only under CO2 pressure. 1H NMR spectroscopy of the products from all insertion reactions reveals strongly solvent-dependent chem. shifts and restricted rotation around the N-C(:X) bonds. Carbonyl sulfide reacts more rapidly with 1 than does CO2 to yield a structurally characterized O-silylthiourethane deriv., only one mol. of COS could be added. Carbon disulfide reacts rapidly with 1 under partial oxidative desilylation as evident from the formation of pyrazine; in addn. to some insertion, a novel polyheterocyclic system I is formed as the main product. The crystallog. characterized red 5r,10c;6t,9t-diepiazano-thiocino[4,5-b]pyrazine-8-thione deriv. I is formed by cycloaddn. between CS2 and two equiv. of 1; the mol. I contains one boat- and one chair-shaped polyhydropyrazine ring and a close to tetrahedral arrangement of the four Me3Si groups. [on SciFinder(R)]
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