Intramolecular benzylic C–H activation: palladium-catalyzed synthesis of hexahydromethanofluorenes (original) (raw)
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ChemInform, 2014
Palladium-Catalyzed C-H Acetoxylation of 2-Methoxyimino-2-aryl-acetates and Acetamides.-The direct C-H acetoxylation of the title compounds affords the oxidative coupling products in moderate to good yields. A number of alkyl and alkoxy substituents can be incorporated into the benzene ring at ortho-, meta-, and para positions without significant loss in reaction efficiency. Accordingly, the structural variation of the ester and amide moieties in the acetoxylation reaction is carried out, cf. (VIII). Interestingly, changing the solvent to tBu-COOH results in a pivaloyloxylation product. Furthermore, the resulting α-imino esters can be easily converted into naturally unprecedented α-amino acids in almost quantitative yields.-(WANG, L.;
Chemical and Pharmaceutical Bulletin
C-H functionalization reactions involve the activation of otherwise unreactive C-H bonds, and represent atom economical methods for the direct transformation of simple substrates to complex molecules. While transition metal-catalyzed C(sp 2)-H functionalization reactions are regularly used in synthesis, C(sp 3)-H functionalization is rarely applied to the synthesis of complex natural products because of the difficulties associated with controlling selectivity. With this in mind, we focused on the development of new palladium (Pd)(0)-catalyzed C(sp 3)-H functionalization reactions for the synthesis of complex molecules, resulting in several new methods capable of solving these problems. We initially developed a concise synthetic method for the facile construction of oxindoles and spirooxindoles via a Pd-catalyzed benzylic C(sp 3)-H functionalization reaction. This method was subsequently extended to the synthesis of various heterocycles, including 2-arylindoles, benzocarbazole, indolocarbazole, indoloquinazolinone, and indoloquinazolinedione, as well as the total synthesis of several pyrrolophenanthridine alkaloids without the need for any protecting groups. This method was also successfully applied to the synthesis of the right-hand fragment of benzohopane from tetrahydro-2H-fluorene, which was constructed by a Pd-catalyzed benzylic C(sp 3)-H functionalization. In this review, we provide a detailed discussion of our most recent investigations pertaining to Pd(0)-catalyzed benzylic C(sp 3)-H functionalization.
2012
Palladium-catalysed coupling reactions have been embraced by synthetic chemists as one of the preferred means for smooth formation of new carbon-carbon bonds: a truly ubiquitous methodology of synthesizing complex molecules. This thesis describes the study of a series of palladium(0)-catalysed C2-arylations of a 1cyclopentenyl ether, equipped with a chiral (S)-N-methyl-pyrrolidine auxiliary. The investigated olefin was demonstrated to undergo Si-face insertion, providing (R)-configuration of the arylated C2-carbon. In addition, the mild and novel palladium(II)-catalysed dominoHeck/Suzuki β,α-diarylationreduction of a dimethylaminoethyl-substituted chelating vinyl ether was developed using arylboronic acids as arylating agents in combination with 1,4-benzoquinone (BQ). Further, highly regioselective palladium(II)-catalysed α-and β-monoarylation of the chelating vinyl ether was achieved using either a bidentate ligand or by employing ligand-less conditions. These studies demonstrate that the choice of ligands has a profound effect on the reaction outcome, as productive β,α-diarylation could only be obtained by suppressing the competing β-hydride elimination using BQ as the stabilising ligand and terminal reoxidant. The pivotal role of BQ in the reaction was studied using computer-aided density functional theory calculations. The calculations highlight the crucial role of BQ as a Pd(II)-ligand. In addition of serving as an oxidant of palladium, the calculations support the view that the coordination of BQ to the Pd(II)-centre in the key σ-alkyl complex leads to a low-energy pathway, aided by a strong η 2 Pd-BQ donation-back-donation interaction. Furthermore, an investigation of the scope and limitations of novel stereoselective and BQ-mediated palladium(II)-catalysed domino Heck/Suzuki β,α-diarylation reactions, involving metal coordinating cyclic methylamino vinyl ethers and a number of electronically diverse arylboronic acids, conducted. In addition, a set of 4-quinolone-3-carboxylic acids, structurally related to elvitegravir and bearing different substituents on the condensed benzene ring, was designed and synthesized as potential HIV-1 integrase inhibitors. Finally, in an effort to identify a new class of HIV-1 protease inhibitors, four different stereopure β-hydroxy γ-lactam-containing inhibitors were synthesized, biologically evaluated, and co-crystallized with the enzyme.
Article A Study of Palladium Catalyzed Intra/Intermolecular Cascade
2014
The compounds [3-(2-Bromocyclohex-2-enyloxy)prop-1-ynyl]-tert-butyldimethylsilane 3, [4-(2-bromocyclohex-2-en-1-yloxy)but-2-yn-1-yloxy]tert-butyldimethylsilane 5 and dimethyl 2-(2-bromocyclohex-2-enyl)-2-(3-(tert-butyldimethylsilanyl)prop-2ynyl)malonate 9 were prepared and subjected to palladium-catalyzed intra-intermolecular cascade cross couplings incorporating bicyclopropylidene 10 under two types of conditions. In the presence of Pd(OAc) 2 , PPh 3 and K 2 CO 3 in acetonitrile at 80 °C, the products were indene analogues, cross-conjugated tetraenes 11, 12 and 13, respectively. The corresponding spirocyclopropanated tricycle 16 in dimethylformamide at 110 °C was obtained, albeit in low yield (24%), and observed as an equimolar mixture of diastereomers, whereas 14, 15 were not fully isolated.
Journal of Organometallic Chemistry, 1999
The palladium-catalyzed arylation and alkenylation of alkenes, generally called the Heck reaction, has been applied to a number of new concepts. Starting from simple, oligohalogenated alkenes and arenes, the synthesis of a variety of highly functionalized carbon skeletons has been established. The domino-type combination of an intramolecular Heck with an inter-or intramolecular Diels-Alder reaction has been shown to provide facile access to interesting bicyclic and tetracyclic frameworks. While intramolecular Heck reactions on trisubstituted, cyclopropylidene-terminated alkenes proceeded with retention of the cyclopropyl moiety, tetrasubstituted alkenes with methylenecyclopropane end groups reacted with ring opening to yield cross-conjugated trienes. The study of the palladium-catalyzed oligocyclizations of 2-bromoalka-1,(v-1)-diene-n-ynes has revealed interesting and useful systematics as to achievable ring size combinations and skeletal types. Highly functionalized methylenecyclopropanes are conveniently accessible via palladium-catalyzed allylic substitution reactions of 1-ethenylcyclopropyl sulfonates and chlorides as well as cyclopropylideneethyl esters which proceed with complete regioselectivity in most cases.
New catalytic methods for the synthesis of selectively substituted aromatics through palladacycles
Pure and Applied Chemistry, 2005
Joint palladium and norbornene catalysis for selective aromatic functionalization via palladacycles is reported. Both alkylation and arylation of aromatics are considered after a brief outlook on the mechanism. These are multistep reactions that proceed in ordered sequences and are chemio-, regio-, and stereoselective. The study of the single steps with isolation of the organometallic species involved has allowed us to detect subtle steric and electronic effects which have been exploited to achieve catalytic reactions. Recent developments of aromatic alkylation and arylation are reported, in particular, condensed heterocyclic ring formation involving dialkylated arylpalladium complexes or both symmetrically and unsymmetrically substituted biphenylylpalladium complexes.