Thioether palladium

Thiols add to alkenes under photochemical conditions to form thioethers, and the reaction can be done intramolecularly to give cyclic thioethers. Thiols also add to alkynes and with a palladium catalyst, vinyl sulfides can be formed. " Selenium compounds (RSeH) add in a similar manner. ... 

Regarding the use of other metals for this transformation, Shirai and co-workers reported that a system constituted by palladium(II) complex [Pd(p-Cl)(r -aUyl)]2 and thioether-imidazolium chloride 19 achieved the arylation of aldehydes with boronic acids [33] and potassium trifluoroborates in good to excellent yields (Scheme 7.5) [34], More recently, Buffard and Itami showed that a NKcod) / IPr-HCl system could catalyse the reaction of arylboronate esters and inactivated aldehydes and ketones (Scheme 7.5) [35]. 

Since carbohydrates constitute an inexpensive and highly modular chiral source for preparing chiral ligands," Claver et al. have reported the use of a series of thioether-phosphite" and thioether-phosphinite furanoside ligands" in the test palladium-catalysed allylic substitution reaction. In the first type of ligand, a systematic variation of the donor group attached to the carbon atom C5 indicated that the presence of a bulky phosphite functionality had a positive effect on the enantioselectivity. Indeed, the enantioselectivity was controlled mainly by the phosphite moiety. This was confirmed by the use of a ligand... 

Several Pd11 complexes with thiolate or thioether derivative ligands have been studied to be applied in the hydroxycarbonylation reaction.394 Aminothiolate complexes of palladium with PPh3 catalyze the conversion of styrene to 2-phenylpropionic acid in high yield and excellent regioselectivity.644 Under mild conditions and in the presence of a catalytic amount of an S, TV-chelated palladium or//zo-amino-arenethiolate complex, styrene reacts with CO and oxalic acid or water to selectively give 2-phenylpropanic aid in high yield.645... 

Pyrimidine thioethers may also be synthesized via direct Pd-catalyzed C—S bond formation between halopyrimidines and thiolate anions. For very unreactive thiol nucleophiles such as 2-thiopyrimidine, both a strong base and a palladium catalyst are essential. Without a palladium catalyst or replacing f-BuONa with K2C03, the reaction failed to furnish the desired pyrimidine thioether [49]. 

A novel route to 2,3-dihydrothiophenes involved a titanocene-promoted carbene formation and subsequenct intramolecular cyclization onto a thiol ester <99SL1029>. Treatment of thioacetal 9 with the low-valent titanium complex 10 gave 2,3-dihydrothiophene 12 by intramolecular olefination of the thiol ester of titanium-carbene intermediate 11. Another metal-mediated cyclization onto the thiophene ring system involved the palladium-catalyzed cyclization of 1,6-diynes <99T485>. For example, treatment of thioether 1,6-diyne 13 with Pdlj in the presence of CO and Oj in methanol followed by treatment with base gave 14. 

Both 6-alkanesulfanyl- and 6-alkanesulfonylpurines proved competent coupling partners in the palladium-catalyzed Suzuki reaction with boronic acids when an imidazolium carbene ligand was used <20050L1149>. The sulfones were found to be significantly more reactive (60 °C, THF) than the thioethers (90 °C, toluene) (Scheme 44). 

That sulfides coordinate to palladium(II) more strongly than the corresponding sulfoxides has received an interesting confirmation in a study of the complexes (19)-(21) (R = 4-MeQjHt).149 The complex (19) is the best catalyst both for cyclotrimerization of diphenylethyne and for isomerization of allyl ethanoates. In both processes a vacant metal coordination site is essential and the thioether sulfur is too strongly bound (in 20 and 21) for facile dissociation. 

Resin-bound benzylic thioethers can be converted into sulfonium salts by S-alkyla-tion with triethyloxonium tetrafluoroborate. These sulfonium salts react with palladium ) complexes to yield benzylpalladium complexes, which undergo Suzuki coupling with arylboronic acids (Entry 7, Table 3.48),... 

Emslie also reported the ability of the related rigid phosphine-thioether-borane ligand 32 (referred to as PSB) to engage in bridging P-M-Cl-B interaction upon coordination to rhodium and palladium precursors (Scheme 52).7, 76... 

Adachi K, Watarai H (2005) Interfacial aggregation of thioether-substituted phthalocyaninatomagnesium(II)-palladium(II) complexes in the toluene/water system. J Mater Chem 15(44) 4701 1710... 

Palladium-catalyzed annulation of the thioether 26 with various alkenes has been demonstrated to furnish the tricyclic systems 27 in modest yields <07JOC775>. Formation of 2,3-dihydrobenzo[Z>]thiophenes has also been observed upon fluoride induced rearrangement of certain aryl 2-(trimethylsilyl)ethyl sulfoxides <07OBC1595>. 

In a more conventional ligand design, Ros et al. used chiral A -tra 5-2,5-diphenylpyr-rolidinyl imidazole as the starting point to introduce a thioether functionality on a primary alkyl halide carrier (see Figure 4.85) [261], The thioether functionality becomes chiral upon coordination to palladium and the remote chirality effect of the other, the pyrrolidine wingtip group ensures that only one of the two possible sulfur based enantiomers is realised. 

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