Tosylates, transition-metal-catalyzed

The use of aryl tosylates as electrophiles is attractive, since they can be synthesized from readily available phenols with less expensive reagents than those required for the preparation of the corresponding triflates. More importantly, tosylates are more stable towards hydrolysis than are triflates. However, this greater stability renders tosylates less reactive in transition metal-catalyzed coupling reactions. As a result, protocols for traditional cross-coupling reactions of these electrophiles were only recently developed [1], In contrast, catalytic direct arylations with aryl tosylates were not reported previously. However, a ruthenium complex derived from heteroatom substituted secondary phosphine oxide (HASPO) preligand 72 [81] allowed for direct arylations with both electron-deficient, as well... 

The scientific contributions from the Ph.D. work of Thomas M. Gdgsig falls specifically into this category. Thomas M. Gdgsig has worked in a very competitive area of expertise dealing with the discovery or improvement of a number of transition metal-catalyzed transformations, including (a) studies on Pd-catalyzed 1,2-migra-tion reactions, (b) Pd-catalyzed Heck reactions employing heteroaromatic tosylates, (c) Ni-catalyzed Heck reactions, and (d) Pd-catalyzed carbonylation reactions... 

During the last decades much effort has been directed towards the implementation of alcohol derived electrophiles different from the costly and often unstable triflates and nonaflates. The corresponding phosphates and tosylates, representing a more stable and less costly alternative to the traditional sulfonates, have been successfully utilized in a number of processes including the transition metal catalyzed Suzuki, Kumada and Negishi reactions reported by Skrydstmp and... 

Scheme 5.1 Transition metal catalyzed reactions utilizing pyridyl tosylates...

In this context, the use of ionic liquids with halogen-free anions may become more and more popular. In 1998, Andersen et al. published a paper describing the use of some phosphonium tosylates (all with melting points >70 °C) in the rhodium-catalyzed hydroformylation of 1-hexene [13]. More recently, in our laboratories, we found that ionic liquids with halogen-free anions and with much lower melting points could be synthesized and used as solvents in transition metal catalysis. [BMIM][n-CgHi7S04] (mp = 35 °C), for example, could be used as catalyst solvent in the rhodium-catalyzed hydroformylation of 1-octene [14]. 

As stated above, aliphatic amines are potent ligands for electrophilic transition metals and are efficient catalyst poisons in attempted alkene animation reactions. However, tosylation of the basic amino group greatly reduces its complexing ability, yet does not compromise its ability to nucleophilically attack complexed alkenes. Thus, a variety of alkenic tosamides efficiently cyclized under palladium(II) catalysis producing N-tosylenamines in excellent yield (equations 17 and 18).32 Again, this alkene amination proceeded through an unstable a-alkylpalladium(II) species, which could be intercepted by carbon monoxide, to result in an overall aminocarbonylation of alkenes. With ureas of 3-hydroxy-4-pentenyl-amines (Scheme 7), this palladium-catalyzed process was quite efficient but it was somewhat less so with... 

Although diaryliodonium salts are generally synthesized under transition metal-free conditions, an interesting rhodium- and copper-catalyzed synthesis was recently published. Arenes with N-containing directing groups were reacted with DIB/TsOH to provide aryl(phenyl) tosylates (Scheme 4b) which were chemoselectively applied in various metal-catalyzed transformations [86]. Salts with an oxime ether substituent could be obtained under rhodium- and silver-catalyzed conditions (see Sect. 3.1.2) [86]. 

---