Carbon-carbon bond forming reactions at C-2 of the thiazole ring have been carried using two strategies, one involving the addition of organometallic reagents (lithium carbanions of esters, Grignard salts, silyl enol ethers, silyl ketene acetals, silylazoles) to N-acylthiazolium salts; the other involving the addition of carbon electrophiles (ketenes, acyl chlorides, anhydrides, aldehydes) toN-acylthiazolium ylides generatedin situ. The reactions have been applied to 1,3-thiazole and 2-trimethylsilyl-1,3-thiazole, the latter being more reactive than the former toward electrophiles. This methodology constitutes a new entry to a variety of functionalized thiazoles and thiazolines which are potential building blocks for the synthesis of natural compounds and analogues of biologically active molecules (penems, arylpropionic acids). Some ring transformations of thiazoles induced by carbon-sulfur bond cleavage are also described. The fundamental role played by the sulfur atom of the thiazole ring in the observed reactions is pointed out and briefly discussed.