Palladium-Catalyzed Allylation of Acidic and Less Nucleophilic Anilines Using Allylic Alcohols Directly

Abstract

A principal goal of organometallic chemistry is the catalytic synthesis of organic compounds by using the chemistry of organic ligands covalently bound to transition metals. Most organometallic chemistry has focused on complexes with covalent metal-carbon or metal-hydrogen bonds. Transition metals have been workhorse elements in many commercialized catalytic processes that include hydrogenations, hydroformylations, acetic acid production, and other C-C and C-H bond forming processes. [1][2][3][4][5] Although carbon-oxygen, carbon-nitrogen, or carbon-sulfur bonds are found in the majority of important organic molecules, catalytic organometallic reaction chemistry that leads to the formation of carbon-heteroatom bonds is less common than that forming carbon-carbon and carbon-hydrogen bonds. Transition metal h 3 -allyl complexes, as well as transition metal s-alkyl complexes, play important roles as active species and key intermediates in many reactions catalyzed by transition metal complexes.6) The palladium-catalyzed allylation is an established, efficient, and highly stereo-and chemoselective method for C-C, C-N, and C-O bond formation, which has been widely applied to organic chemistry. [7][8][9][10] The processes have been shown to proceed by attack of nucleophiles on intermediate h 3 -allylpalladium(II) complexes generated by oxidative addition of allylic compounds including halides, [11][12][13] esters, [14][15][16][17][18][19][20][21][22][23][24][25][26] carbonates, [27][28][29][30][31][32][33][34][35][36] carbamates, [37][38][39] phosphates, [40][41][42] and related derivatives [43][44][45][46][47][48][49] to a Pd(0) complex. Because these substrates are synthesized from the corresponding allylic alcohols, palladium-catalyzed conversion of allylic alcohols directly into allylation products are highly desirable, especially from the viewpoint of the atom economy. 50,51) For achieving the palladium-catalyzed C-O bond cleavage of allylic alcohols, various other processes to facilitate the bond cleavage have been reported. 52) These processes include conversion of allylic alcohols into the esters of inorganic acids (e.g., SnCl 2 61-64) ). However, there have been only limited and sporadic reports dealing with the direct cleavage of the C-O bond in allylic alcohols on interaction with a transition metal complex. [65][66][67][68][69][70][71][72] Successful applications using allylic alcohols directly in catalytic processes are even more limited. This apparently stems from the poor capability of a nonactivated hydroxyl to serve as a leaving group. 59,60) We have recently reported our attempts and some successful applications of a process involving the C-O bond cleavage with direct use of allylic alcohols catalyzed by palladium complexes. [73][74][75][76] Herein, we report the application of this methodology to the palladium-catalyzed allylation of acidic and less nucleophilic anilines 77-80) using allylic alcohols directly. The allylation process is straightforward. We studied the reactions of acidic and less nucl...

Simple palladium‐catalyzed C–N bond formation for poor nucleophilicity of aminonaphthalenes

“…Compounds 3a , 4a , 3b , 4b , 3c , 4c , 3 d , 3e , 3f , 3 g , 4 g , 3 h , 3i , 11 , 12 , 13 , and 14 were synthesized according to the general procedure (for reaction time see Tables and ).…”

Procedures for and Possible Mechanisms of Pd‐Catalyzed Allylations of Primary and Secondary Amines with Allylic Alcohols

“…Yang et al have intensively developed the use of titanium(IV) isopropoxide and molecular sieves as additives for the allylation of primary and secondary arylamines with various allylic alcohols [43,[48][49][50][51][52][53][54][55] [Equation (20)]. [55] No reaction was observed without the titanium alkoxide [Equation (21)], [43] and the yields decreased greatly in the absence of the molecular sieves.…”

“…[55] No reaction was observed without the titanium alkoxide [Equation (21)], [43] and the yields decreased greatly in the absence of the molecular sieves. [48,51] The best catalytic system would be highly dependent on the structure of the amine; for an example, the reaction between 1 and aniline in benzene gave much better results with Pd(OAc) 2 /PPh 3 than with PdCl 2 /PPh 3 [Equation (22)], [48] while the yields were similar with 1-aminonaphthalene [Equation (23)].…”

“…[51,53,55] The PdL n /Ti(OR) 4 /MS procedure has been applied to the synthesis of heterocycles from (Z)-but-2-ene-1,4-diol and 2-aminophenols [Equation (25)], [50,54] o-phenylenediamines [Equation (26)], [52] or 2,3-diaminonaphthalene. [53,56] Other Ti(OR) 4 variants can be used, [52][53][54] while use of TiCl 4 resulted either in no reaction [52] or in low yields.…”

“…Pd-catalyzed trans to cis isomerization of the η 3 -allylpalladium intermediate is also a possibility. [61] Yang's team, who had previously used the PdL n /Ti-(OR) 4 /MS procedure in benzene for allylation of anilines, [40,[48][49][50][51]55] has recently reported the use of a carboxylic acid as the additive at reflux in water [Equations (31)- (33)]. [62] A screening of carboxylic acids and palladium/ligand combinations resulted in the retention of adamantane-1-carboxylic acid (AdCO 2 H) and Pd(acac) 2 /PPh 3 for the performance of various allylic aminations.…”