Thioketenes special

Isothiocyanates (70LA(731)120) and bis(trifluoromethyl)thioketene (78JOC2500) have also been reported to add to benzalimines but these are undoubtedly special cases (Scheme 94). 

As for thioaldehydes, the stability of thioketenes is largely influenced by the nature of the substituents and bulky groups tend to stabilize this functional group. Electronic factors such as those originating in silicon, phosphorus or trifluoromethyl substituents lead to a similar result. In general, however, the synthesis of monomeric thioketenes is difficult and requires the use of special techniques such as FVT, matrix isolation at low temperatures or generation under conditions which allow trapping in situ of the transient species. The... 

The cycloaddition reactions are subdivided into di-, tri- and oligomerization reactions, [2-1-1]-, [2-1-2]-, [3-1-2]- and [4- -2] cycloaddition reactions and other cycloaddition reactions. The insertion reactions into single bonds are also discussed. The cyclodimerization or cyclotrimerization reactions are special examples of the [2-1-2] and the [2-I-2-I-2] cycloaddition reactions, respectively. The cumulenes vary in their tendency to undergo these reactions. The highly reactive species, such as sulfines, sulfenes, thioketenes, carbon suboxide and some ketenes, are not stable in their monomeric form. Other cumulenes have an intermediate reactivity, i.e. they can be obtained in the monomeric state at room temperature and only heat or added catalysts cause di- or trimerization reactions. In this group, with decreasing order of reactivity, are allenes, phosphorus cumulenes, isocyanates, carbodiimides and isothiocyanates. 

Thioketens from, l, i-Thiadiazoles. The synthesis of thioketens from 1,2,3-thiadiazoles, projected by Staudinger in 1916, has now been achieved on a convenient preparative scale (1—10 g), in good yield, by the flash thermolysis of 1,2,3-thiadiazoles at 580 °C and 10 Torr in a specially designed apparatus. The thermolysis of 1,2,3-thiadiazoles, preferably in boiling diglycol, also provides a practical source of thioketens for immediate further synthetic use, e.g. in the production of thioesters, as shown in Scheme 1. The use of 4- and 5-phenyl-l,2,3-... 

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