α-Arylchalcogenation of Aldehydes and Ketones with Diaryl Dichalcogenides Promoted by K3PO4

A new catalytic method for direct α-arylchalcogenation reaction of aldehydes and ketones has been developed. When various aldehydes and ketones were allowed to react with diaryl dichalcogenides in the presence of K3PO4, under mild reaction condition, the corresponding α-phenylselenoand α-arylthio aldehydes and ketones were obtained in good to high yields.

Recently, we reported a simple and very efficient procedure for α-phenylselenenylation of aldehydes and ketones from the corresponding aldehydes or ketones and diphenyl diselenide in the presence of KF/Al 2 O 3 [35].In the same year, similar reaction utilizing Cs 2 CO 3 , as catalyst, was reported by Nishiyama and co-workers [36]; however, this catalyst was largely successful on ketones, and complex reaction mixtures was observed for aldehydes.Driven by our continuing interest on the K 3 PO 4 -mediated reactions [37,38] and with the aim to expand its application, we want to present herein its utility in the synthesis of α-arylchalcogeno aldehydes and ketones by reaction of varius aldehydes and ketones with diaryl dichalcogenides.
Tripotassium phosphate continues to attract much attention from organic chemists due to the versatility of use in synthetic chemistry; it is cheap, non-toxic, and a strong inorganic base (pKa 12.32 for the conjugate acid), used as an alternative non-nucleophilic base in several reaction [39][40][41][42].
Encouraged by these results, the scope of this methodology was extended to K 3 PO 4mediated reaction of carbonyl compounds with diphenyl ditelluride and various disulfides (Scheme 3, Table 3).As in the case of diphenyl diselenide, disulfides can also react Scheme 3  different aldehyde and ketones under the same reaction conditions.It was observed that ketones require longer reaction times to afford the respective α-arylthio derivatives 6b-g (Table 3, entries 2-7).We also noted that the reaction yields were slightly lower when cyclic ketone, cyclohexanone, was used.However, under the same conditions, the treatment of nheptanal and 3-pentanone with diphenyl ditelluride did not produce the expected αphenyltelluro derivatives 6h and 6i even after 24 h.

Conclusion
In conclusion, we have developed a new convenient and efficient protocol for αarylchalcogenation of aldehydes and ketones with diaryl dichalcogenides in the presence of K 3 PO 4 under mild reaction conditions with good to high yields.This process represents a suitable option to existing methods.

General procedure
To a stirred solution of aldehyde or ketone (3.0 mmol) and anhydrous K 3 PO 4 (1.5 mmol) in dry DMSO (2 cm 3 ), diaryl dichalcogenide (1.0 mmol) was added.Stirring of the resulting reaction mixture was continued at 40 ºC for the appropriate time (Tables 2 and 3).After the reaction was complete (monitored by TLC) the mixture was filtered and the solid, K 3 PO 4 , was washed thoroughly with EtOAc (25 cm 3 ).The filtrate was washed with water (2 × 20 cm 3 ) and dried over anhydrous MgSO 4 .The solvent was evaporated to give the crude product which was purified by preparative TLC (silica gel, eluent n-hexane:EtOAc = 10:1

9 a
Isolated yields.

Table 1
Optimization of reaction conditions
a Isolated yields.