Ligandless Pd catalysts

Acylpalladium was generated by the oxidative addition of acyl chloride 98 to Pd(0), and reacted with 1,1-dimethylallene (99) to give tt-allylpalladium intermediate 100. Then transmetallation of 100 with diborane and reductive elimination provided 2-acylallylboronate 101. Thus highly regio- and stereoselective acylboration of allenes occurred using ligandless Pd catalyst [44]. 

These potassium organotrifluoroborates are good partners of S-MC [26]. Coupling of PI1BF3K (20) with deactivated / -bromoanisole proceeds with ligandless Pd catalyst in refluxing MeOH in the presence of K2CO3 [27]. Reaction of more... 

Some halides on silicon are activating groups. Generally two fluorine atoms are required for aryl-aryl coupling. For example, coupling of ethyl(2-thienyl)difluoro-silane (9) with 3-iodothiophene 10 afforded the bisthiophene 11 using a ligandless Pd catalyst in the presence of KF [87]. 

The alkenylsiletane 44 is very reactive and reacts with 4-iodoanisole (2) at room temperature with ligandless Pd catalyst in 10 min to give 46 in 94% yield [97]. Here again 44 is considered to be transformed to a silanol before coupling. 

Coupling of the silanol 47 with electron-deficient 4-iodoacetophenone proceeded at room temperature in 10 min to afford 49 in 79 % yield using ligandless Pd catalyst. Also coupling with the less reactive aryl iodide 2 occurred efficiently with ligandless Pd catalyst [99]. 

The coupling products are obtained by one-pot hydrosilylation/cross-coupling of alkynes. Pt-catalyzed hydrosilylation of alkyne with tetramethyldisiloxane (52) generates the alkenylsilane 53, which is coupled with 4-iodoanisole (2) using ligandless Pd catalyst and TBAF at room temperature to afford 46 in 84 % yield [103]. 

Smooth reactions with ligandless Pd catalysts. The process shows a new and... 

Unsaturated esters are prepared by the carbonylation of allylic compounds under various conditions depending on the leaving groups. Carbonylation of allylic chlorides proceeds under two-phase (liquid-solid) and mild conditions (room temperature, 1 atm of CO in the presence of K2CO3 in EtOH) using ligandless Pd catalyst. Ethyl 4-phenyl-3-butenoate was obtained from cinnamyl chloride in 94% yield [143]. Allylic carbonates are reactive and their carbonylation proceeds under mild neutral conditions [144]. 

Highly vmsaturated lactone 403 was obtained by an intramolecular reaction of 2-(propargyl)allyl phosphate 398 with CO (1 atm) catalyzed by ligandless Pd catalyst in the presence of Cy2NMe. As an explanation, the acylpalladium 400 is converted to the ketene 401, and the palladacycle 402 is generated by oxidative cyclization. Insertion of CO to 402 and reductive elimination provide 403 [154]. 

Tamaru and co-workers reported that benzaldehyde and butadiene are formed from 6-phenyl-4-vinyl-1,3-dioxacyclohexan-2-one (521) at room temperature using ligandless Pd catalyst. Facile C—C bond cleavage (j6-carbon elimination or 6-decarbopalladation) in the intermediate palladacycle 522 occurs. As an extension. 

Formation of 7r-allylpalladium enolates by the reaction of the silyl enolate 539 with allyl carbonate is summarized as follows. The enolate of cyclohexanone is treated as a model compound here. Transmetallation of 7r-allylpalladium methoxide 538 with the silyl enolate 539 generates either Pd enolates 540 or a-palladake-tone 541. Reductive elimination affords allylcyclohexanone 542 in THF [200]. At higher temperature, cyclohexanone 543 is obtained by elimination using ligandless Pd catalyst in MeCN [201]. 

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