Thioketones thiolate

Barton and coworkers exploited this strategy in the preparation of overcrowded ethylenes456 usually the desulfurization of a thiirane is accomplished by one equivalent of tertiary phosphine, mainly triphenylphosphine. However, spontaneous loss of sulfur from thiiranes substituted by aryl or halogen has sporadically been reported. Huisgen has reviewed this subject455 and performed many kinetic studies. He found that the desulfurization step can be accomplished by catalytic thiolates and also by thiobenzophenone or other thioketones, although in this case the reaction is slower (equation 131). 

It was mentioned earlier that thiocarbonyl thiolates reacted with thioketones forming 1,2,4-trithiolates <1987JA902>. Aromatic thioketones (e.g., thiobenzophenone) are super-dipolarophiles and at 80 °C in a three-reagent mixture with phenyl azide and cyclobutanethiones they form spiranic compounds with X = CO, CS, or CH2 (Equation 21) <1995HCA1298>. An X-ray study of the compound with Ar = 4-MeOC6H4 confirmed the molecular stmcture. 

Enedithiolate anions are redox-active ligands (see equation 1), capable of coordinating with a variety of metals as neutral dithioketones (1), thioketone radical thiolate monoanions (2) and ene-l,2-dithiolate dianions (3). The complexes are named dithiolenes irrespective of their oxidation state to remind one that they are noninnocent ligands . 

The general reaction mechanism has been shown to involve typical steps for cross-coupling [98, 113]. Oxidative addition of an aryl halide generates a Pd(II) species that undergoes transmetalation to form a Pd(II)-thiolate. C-S reductive elimination provides the aryl sulfide and regenerates the Pd(0) catalyst. More recently, Hartwig reported a detailed mechanistic analysis of the Pd/Josiphos system derived from different Pd precursors. The dominant Pd species were found to be off the catalytic cycle, which accounted for differences in rates between stoichiometric and catalytic reactions [114]. Thioketones are also effective thiolate nucleophiles for C-S bond formation. The reaction involves tandem Pd-catalyzed thioenolate alkylation, followed by 5-arylation (8) [102]. Presumably, the arylation process proceeds by a similar mechanism to related Pd-catalyzed transformations. 

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