Electrophiles thioketene

StericaHy hindered or very electrophilic substituted ketenes, such as diphenylketene, di-Z rZ-butylketene [19824-34-17, and bis(trifluoromethyl)ketene, are quite stable as monomers. Ketenimines tend to polymerize. The dimerization of thioketenes results in 1,3-dithiacyclobutanones (6) (45), a type of dimer not observed with ketenes. 

Due to the highly nucleophilic and polarizable thiocarbonyl sulfur, thioketones react with a large variety of electrophiles E+. In the case of thioaldehydes and thioketenes this... 

Addition of phenylethynethiolate or -selenate to the carbene complex 185 (M = Cr or W, R = Me or Et, E = S or Se) affords an anionic adduct (186) which, unexpectedly, contains a reactive thioketene function. Electrophiles can attack either at the sulfur or at the carbon a thereto to produce coordinated carbenes or thio- and seleno aldehydes and esters [H4J45). 

As mentioned in various sections, nucleophilic addition of phenylethyn-ethiolate or phenylethyneselenolate, PhC=CE (E = S or Se), to the car-bene complex [W(CO)s C(OEt)Ph)] affords thioketene adducts (186), which, depending on the electrophile used, function as electrophilic synth-ons for either coordinated thio- or selenoacyl anions, [W(CO)5E=CR] , or their structural isomers, anionic thio- or selenocarbene complexes. 

Thioketenes (34) are highly electrophilic and give a smooth reaction with ammonia or amines. In fact, addition of a secondary amine offers the best way to scavenge a suspected thioketene. But the approach also deserves interest from the point of view of thioamide synthesis as it allows very mild and nonreducing conditions, tolerating the presence of sensitive additional functional groups such as cyano, nitro, or sulfonyl residues (equation... 

Cationic and Anionic Cyclizations. The thioketene acetals derived from the reaction of anion (1) have found several applications in cyclization methodology. The thioketene acetals can be used as either electrophiles (eq 7) or nucleophiles (eq 8) in a cyclization process which depends on the experimental conditions. 

---