A Concise Palladium-Catalyzed Carboamination Route to (±)-Tylophorine

Recent Advances in 1,2-Amino(hetero)arylation of Alkenes

Alkene amino(hetero)arylation presents a highly efficient and straightforward strategy for direct installation of amino groups and heteroaryl rings across a double bond simultaneously. An extensive array of practical transformations has been developed via alkene difunctionalization approach to access a broad range of medicinally valuable (hetero)arylethylamine motifs. This review presents recent progress in 1,2-amino(hetero)arylation of alkenes organized in three different modes. First, intramolecular transformations employing C, N-tethered alkenes will be introduced. Next, two-component reactions will be discussed with different combination of precursors, N-tethered alkenes and external aryl precursor, C-tethered alkenes and external amine precursor, or C, N-tethered reagents, and alkenes. Last, three-component intermolecular amino(hetero)arylation reactions will be covered.

Concise asymmetric syntheses of novel phenanthroquinolizidines

The first preparation of enantioenriched phenanthroquinolizidines with a quaternary center at C14a was accomplished in seven steps from readily available starting materials. Key steps were an efficient dynamic kinetic allylation of a diastereomeric mixture of chiral tert-butylsulfinyl ketimines and the construction of a piperidine E ring by rhodium catalyzed hydroformylation. The Stevens rearrangement of the corresponding N-benzyl derivatives took place smoothly, allowing the installation of a benzyl moiety at C9 in a trans relationship with the methyl group. The cytoxicity of the prepared phenanthroquinolizidines was evaluated against different human cancer cell lines.

Short asymmetric synthesis of phenanthroindolizidines through chiral homoallylic sulfinamines

An efficient stereocontrolled preparation of chiral phenanthroindolizidines is detailed. The synthesis relies on the stereoselective indium-mediated allylation of 2-(phenanthren-9-yl)acetaldehyde derivatives with chiral tert-butylsulfinamide. Chemoselective transformations from the corresponding homoallylic sulfinamine allow the synthesis of the phenanthroindolizidines in only three synthetic operations, without any detectable racemization. Following this procedure, the synthesis of natural (-)-tylophorine was successfully accomplished.

Intramolecular aminocyanation of alkenes by N-CN bond cleavage

A metal-free, Lewis acid promoted intramolecular aminocyanation of alkenes was developed. B(C6F5)3 activates N-sulfonyl cyanamides, thus leading to a formal cleavage of the N-CN bonds in conjunction with vicinal addition of sulfonamide and nitrile groups across an alkene. This method enables atom-economical access to indolines and tetrahydroquinolines in excellent yields, and provides a complementary strategy for regioselective alkene difunctionalizations with sulfonamide and nitrile groups. Labeling experiments with (13)C suggest a fully intramolecular cyclization pattern due to the lack of label scrambling in double crossover experiments. Catalysis with Lewis acid is realized and the reaction can be conducted under air.

An enantioselective strategy for the total synthesis of (S)-tylophorine via catalytic asymmetric allylation and a one-pot DMAP-promoted isocyanate formation/Lewis acid catalyzed cyclization sequence

A novel total synthesis of (S)-tylophorine is reported, featuring asymmetric allylation and cascade isocyanate formation and cyclization.

Palladium-catalyzed annulation of 2,2'-diiodobiphenyls with alkynes: synthesis and applications of phenanthrenes

A range of phenanthrene derivatives were efficiently synthesized by the palladium-catalyzed annulation of 2,2'-diiodobiphenyls with alkynes. The scope, limitations and regioselectivity of the reaction were investigated. The described method was adopted to synthesize 9,10-dialkylphenanthrenes, sterically overcrowded 4,5-disubstituted phenanthrenes and phenanthrene-based alkaloids. Reactions of highly methoxy-substituted biphenyls with 2-(2-propynyl)pyrrolidine and 2-(2-propynyl)piperidine gave 2-(9-phenanthylmethyl)pyrrolidines and 2-(9-phenanthylmethyl)piperidines, respectively. The products were transformed to phenanthroindolizidine and phenanthroquinolizidine alkaloids by the Pictet-Spengler reaction.

Enantioselective approach to 13a-methylphenanthroindolizidine alkaloids

The first enantioselective approach to 13a-methylphenanthroindolizidine alkaloids is reported, featuring an efficient stereoselective Seebach's alkylation and Pictet-Spengler cyclization. The proposed and other three most probable structures were ruled out, indicating hypoestestatin 1 needs further assignment.

Recent Developments in Pd-Catalyzed Alkene Aminoarylation Reactions for the Synthesis of Nitrogen Heterocycles

This short review describes new developments in Pd-catalyzed aminoarylation reactions between aryl halides and alkenes bearing pendant nitrogen nucleophiles. These transformations provide a novel and powerful method for accessing numerous 3-, 5-, 6-, and 7-membered nitrogen heterocycles.

Total synthesis of the marine metabolite (±)-polysiphenol via highly regioselective intramolecular oxidative coupling

(±)-Polysiphenol (1), an atropisomerically stable 4,5-dibrominated 9,10-dihydrophenanthrene from Polysiphonia ferulacea, was prepared by a biomimetically inspired highly regioselective intramolecular oxidative coupling of a dibrominated dihydrostilbene. The installation of the two bromine atoms prior to oxidative coupling prevents further oxidation to a planar aromatized phenanthrene. By this strategy, the synthesis of (±)-polysiphenol was achieved in four steps in 70% overall yield. Synthesis of the naturally occurring 5,5'-(ethane-1,2-diyl)bis(3-bromobenzene-1,2-diol) (2) (the likely biogenetic precursor of polysiphenol) and 5,5'-(ethane-1,2-diyl)bis(3,4,6-tribromobenzene-1,2-diol) (9) are also reported. The origins of the regioselectivity in the oxidative coupling are explored.

Asymmetric palladium-catalyzed carboamination reactions for the synthesis of enantiomerically enriched 2-(arylmethyl)- and 2-(alkenylmethyl)pyrrolidines

The enantioselective synthesis of 2-(arylmethyl)- and 2-(alkenylmethyl)pyrrolidine derivatives via Pd-catalyzed alkene carboamination reactions is described. These transformations generate enantiomerically enriched products with up to 94% ee from readily available alkenyl or aryl bromides and N-boc-pent-4-enylamines. The application of this method to a concise asymmetric synthesis of (-)-tylophorine is also discussed.

Use of aryl chlorides as electrophiles in Pd-catalyzed alkene difunctionalization reactions

The development of conditions that allow use of inexpensive aryl chlorides as electrophiles in Pd-catalyzed alkene carboamination and carboetherification reactions is described. A catalyst composed of Pd(OAc)(2) and S-Phos minimizes N-arylation of the substrate and prevents formation of mixtures of regioisomeric products. A number of heterocycles, including pyrrolidines, isoxazolidines, tetrahydrofurans, and pyrazolidines, are efficiently generated with this method.