Palladium(ii) catalyzed thiono-thiolo rearrangement of propargyl thionophosphates

Palladium(II) effectively catalyzes the [3,3]-sigmatropic type rearrangement of propargyl thionophosphates to provide allenyl thiolophosphates specifically.     

钯配合物催化的亚磺酸烯丙酯重排反应

在杂原子酸烯丙酯和低价过渡金属配合物反应的系统研究中,我们发现在四(三苯膦)钯韵催化下,亚磺酸烯丙酯能够容易地重排成相应的砜.反应温度要比相应的热重排低得多,而且时间短,产率高. 重排反应的典型实例如下:在25℃氩气气氛下,向溶有91mg(0.5mmol)苯基亚磺酸烯丙基酯(1a)的5mL四氢呋喃溶液中加入25mg(0.022mmol)四(三苯膦)钯,搅拌反应混合物,薄层层析跟踪直至原料消失,耗时约70分钟.减压除去四氢呋喃,残渣用四氯化碳萃取,硅胶制备薄层层析分离[5:1石油醚(30～60℃)-乙酸乙酯],得79mg油状物,产率87％,b.p.130℃(浴温)/0.2 mm(文献值:111～113℃/0.25mm).结果如表1所示.     

Palladium catalyzed reaction of allylic geminal diacetates with nucleophiles

The influence of ligands on the palladium catalyzed reaction of allylic-1,1-diol diacetate (1) with sodium dimethyl malonate was studied. When PPh₃ was used as the ligand, the malonate anion was found to attack the carbonyl carbon atom, but it would attack the allylic carbon atom while dppe was used as the ligand. The properties of nucleophiles also influence the position of attack. By suitable choice of the nucleophiles and ligands, dialkylated products can be obtained from 1.     

钯催化烯丙基偕二醇二醋酸酯和各种亲核试剂的反应

研究了配体对烯丙基-1,1-偕二醇二醋酸酯(1)在钯配合物催化下和丙二酸酯钠盐反应的影响. 当用PPh3为配位体时, 丙二酸酯碳阴离子进攻在羰基碳上, 当用dppe为配体时, 进攻在烯丙基碳上. 亲核试剂的性质也影响反应进攻的位置. 通过选择适当的亲核试剂和配体可以从1得到二次烷基化的产物.     

Palladium catalyzed allylic C-H alkylation: a mechanistic perspective

The atom-efficiency of one of the most widely used catalytic reactions for forging C-C bonds, the Tsuji-Trost reaction, is limited by the need of preoxidized reagents. This limitation can be overcome by utilization of the recently discovered palladium-catalyzed C-H activation, the allylic C-H alkylation reaction which is the topic of the current review. Particular emphasis is put on current mechanistic proposals for the three reaction types comprising the overall transformation: C-H activation, nucleophilic addition, and re-oxidation of the active catalyst. Recent advances in C-H bond activation are highlighted with emphasis on those leading to C-C bond formation, but where it was deemed necessary for the general understanding of the process closely related C-H oxidations and aminations are also included. It is found that C-H cleavage is most likely achieved by ligand participation which could involve an acetate ion coordinated to Pd. Several of the reported systems rely on benzoquinone for re-oxidation of the active catalyst. The scope for nucleophilic addition in allylic C-H alkylation is currently limited, due to demands on pK(a) of the nucleophile. This limitation could be due to the pH dependence of the benzoquinone/hydroquinone redox couple. Alternative methods for re-oxidation that does not rely on benzoquinone could be able to alleviate this limitation.     

Palladium(0) catalyzed enantioselective rearrangement of O-allylic thiocarbamates to S-allylic thiocarbamates: asymmetric synthesis of allylic thiols

The Pd(0) catalyzed rearrangement of the O-allylic thiocarbamates rac-2a, rac-2b and rac-4 in the presence of the chiral bisphosphane 5 proceeded quantitatively and gave the S-allylic thiocarbamates 6a, 6b and 7, respectively, with 91, 92 and 97% ee, respectively, in high yields. Saponification of the S-allylic thiocarbamate 7 furnished the allylic thiol 9 with 97% ee.     

Palladium complex catalyzed acylation of allylic esters with acylsilanes.

Acylation of allylic esters (2) with acylsilanes (1) in the presence of a catalytic amount (5 mol %) of a palladium complex is reported. The reaction proceeds selectively to afford beta,gamma-unsaturated ketones (3) in high yields. [Pd(eta3-C6H5CH=CHCH2)(CF3COO)]2 (4a) showed the best catalytic activity. After the reaction, formation of CF3COOSiMe3 (5a) was confirmed by 29Si NMR measurement of the resulting reaction mixture, indicating the trimethylsilyl moiety effectively traps the CF3COO leaving group from 2. The leaving group of the allylic esters affects the reaction considerably: allylic trifluoroacetate gave the best result, while the corresponding acetates and trichloroacetates did not afford any acylation products at all. Stoichiometric reaction of 4a with 1 gave acylation product 3 with a formation of 5a and Pd(0), whereas no acylation reaction took place with the corresponding acetate complex [Pd(eta3-C6H5CH=CHCH2)(CH3COO)]2 (4b). A DFT calculation suggests that interaction of high-lying HOMO of 1 and low-lying LUMO of eta3-allylpalladium trifluoroacetate intermediate 4 would be indispensable in the catalytic cycle.     

Palladium catalyzed annulation reaction using a bifunctional allylic alkylating agent

Methylene-cyclopentane and -cyclohexane derivatives were synthesized by the reaction of 2-methylene-propane-1,3-diol diacetate with dicarbanions under the palladium catalysis.     

Tandem Lewis acid catalyzed coupling/semipinacol rearrangement of allylic alcohol

Construction of the polyaryl quaternary unit through a ZnBr2 catalyzed tandem coupling/semipinacol rearrangement participated by allylic cations was reported for the first time.     

Palladium(0) catalyzed 3-aza-cope rearrangement of N-allylenamines

Pd(0) complexes catalyze the 3-Aza-Cope rearrangement of N-allylenamines to the corresponding δ,ε-unsaturated imines or γ,δ-unsaturated carbonyl compounds in the presence of trifluoro-acetic acid as co-catalyst.     

Palladium catalyzed asymmetric allylic alkylation using chelating N-heterocyclic carbene–amino ligands

Several silver(I) complexes with chiral amino-N-heterocyclic carbene (NHC) ligands, which are not diastereomerically pure, were prepared and used to generate in situ chelating NHC–amino palladium(II) complexes. The potential of these palladium(II) complexes in asymmetric catalysis was evaluated in the allylic alkylation reaction. The influence of the structure and of the diastereomeric purity of the ligands on enantioselectivity, as well as the role of the silver salts, were studied. Enantiomeric excesses of up to 80% were obtained with the best ligand.     

Synthesis of nearly enantiopure allylic amines by aza-Claisen rearrangement of Z-configured allylic trifluoroacetimidates catalyzed by highly active ferrocenylbispalladacycles

The development of the first highly active enantioselective catalyst for the aza-Claisen rearrangement of Z-configured allylic trifluoroacetimidates generating valuable almost enantiopure protected allylic amines is described. Usually Z-configured allylic imidates react significantly slower than their E-configured counterparts, but in the present study the opposite effect was observed. Z-Configured olefins have the principal practical advantage that a geometrically pure C=C double bond can be readily obtained, for example, by semihydrogenations of alkynes. Our catalyst, a C(2)-symmetric planar chiral bispalladacycle complex, is rapidly prepared from ferrocene in four simple steps. Key step of this protocol is an unprecedented highly diastereoselective biscyclopalladation providing dimeric macrocyclic complexes of fascinating structure. In the present study as little as 0.1 mol % of catalyst precursor were sufficient for most of the alkyl substituted substrates to give in general almost quantitative yields. NMR investigations revealed a monomeric structure for the active catalyst species. The bispalladacycle can also be used for the formation of almost enantiomerically pure allylic amines (ee > or =96 %) substituted with important functional groups such as ester, ketone, ether, silyl ether, acetal or protected amino moieties providing high-added-value allylic amine building blocks in excellent yield (> or =94 %). The preparative advantages should render this methodology highly appealing as a practical and valuable tool for the formation of allylic amines in target oriented synthesis.     

Palladium(II) catalyzed allylic rearrangement: Stereoselective synthesis of 2-substituted (e)-β acetoxy (or benzoyloxy)ethylidenecyclohexanes

Diastereomeric mixtures of 2-substituted 1-vinyclyclohexyl acetates (or benzoates) are rearranged stereoselectively to 2-substituted (E)-β-acetoxy(or benzoyloxy)ethylidenecyclohexanes by the catalysis of bis(acetonitrile)palladium(II) chloride. A mechanism related to the stereoselectivity and reactivity is discussed in terms of the conformational requirements in a transition state.     

Organo tin nucleophiles iii. Palladium catalyzed reductive cleavage of allylic heterosubstituents with tin hydride

Tributyl tin hydride, serving as an efficient hydride transfer agent, allows highly chemoselective palladium catalyzed reductions of allylic heterosubstituents even in presence of aldehydes, benzyl acetate and benzyl chloride.     

Facile Palladium catalyzed decarboxylative allylation of active methylene compounds under neutral conditions using allylic carbonates

Palladium catalyzed decarboxylative allylation of active methylene compounds proceeded under mild neutral conditions using allylic carbonates, which are much more reactive than allylic acetates or phenoxides used commonly in the reaction.     

Thermal rearrangement of allylic cyanamides

The allylic rearrangement of cyanamides has been achieved by pyrolysis in solution at temperatures between 125 and 190 °C. This rearrangement was also observed during the thermal opening of the aziridine ring in cyanoaziridines. This allylic transposition constitutes a formal method for the 1,3-isomerization of allylic amines.