Mild and Efficient Desymmetrization of Diynes via Hydroamination: Application to the Synthesis of (±)-Monomorine I

Synthesis of 1-pyrroline derivatives via cyclization of terminal alkynes with 2-azaallyls

An efficient transition-metal-free cyclization reaction to prepare 1-pyrroline derivatives bearing various functional groups is described. In this method, a simple combination of a base and a solvent allows the cyclization reaction of terminal alkynes and 2-azaallyls to be carried out efficiently under mild and metal-free conditions. This cyclization reaction will provide an efficient method for the synthesis of medicinally relevant polysubstituted and multifunctionalized pyrrolines.

Hydroelementation of diynes

This review highlights the hydroelementation reactions of conjugated and separated diynes, which depending on the process conditions, catalytic system, as well as the type of reagents, leads to the formation of various products: enynes, dienes, allenes, polymers, or cyclic compounds. The presence of two triple bonds in the diyne structure makes these compounds important reagents but selective product formation is often difficult owing to problems associated with maintaining appropriate reaction regio- and stereoselectivity. Herein we review this topic to gain knowledge on the reactivity of diynes and to systematise the range of information relating to their use in hydroelementation reactions. The review is divided according to the addition of the E-H (E = Mg, B, Al, Si, Ge, Sn, N, P, O, S, Se, Te) bond to the triple bond(s) in the diyne, as well as to the type of the reagent used, and the product formed. Not only are the hydroelementation reactions comprehensively discussed, but the synthetic potential of the obtained products is also presented. The majority of published research is included within this review, illustrating the potential as well as limitations of these processes, with the intent to showcase the power of these transformations and the obtained products in synthesis and materials chemistry.

Tin(iv) chloride mediated (3 + 2) annulation of trans-2-aroyl-3-styrylcyclopropane-1,1-dicarboxylates with nitriles: diastereoselective access to 5-vinyl-1-pyrroline derivatives

A tin(iv) chloride promoted (3 + 2) annulation of trans-2-aroyl-3-styrylcyclopropane-1,1-dicarboxylates with nitriles is reported. The transformation involves the Lewis acid assisted formation of 1,5-dipolar intermediates from the cyclopropane dicarboxylates and nitriles followed by cyclization. The reactions proceed in a highly diastereoselective manner and afford 5-vinyl-1-pyrroline derivatives in 60-88% yields.

Controllable regio- and stereo-selective coupling reactions of homoallenylboronates

Unprecedented palladium-catalysed regio- and stereo-selective coupling reactions of homoallenylboronates with (hetero)aryl iodides, allyl bromides and alkynyl bromides in aqueous solution were successfully developed.

Total Syntheses of (-)-Secologanin, (-)-5-Carboxystrictosidine, and (-)-Rubenine

The first enantioselective total syntheses of (-)-secologanin (1), (-)-5-carboxystrictosidine (2), and (-)-rubenine (3) were accomplished in 10, 9, and 14 steps, respectively. The key transformation in the synthesis of 1 was a sequential anti-selective organocatalytic Michael reaction/Fukuyama reduction/spontaneous cyclization to form an optically active dihydropyran ring. In addition, the secologanin tetraacetate (16), which is a potential key intermediate for the bioinspired divergent syntheses of monoterpenoid indole alkaloids, was prepared in gram-scale in seven steps. The total syntheses of 2 and 3, which are classified as glycosylated monoterpenoid indole alkaloids, were achieved through bioinspired transformations such as a diastereoselective Pictet-Spengler reaction, a site- and stereoselective epoxidation, and a site-selective epoxide ring-opening followed by a lactonization reaction.

Metal-mediated synthesis of pyrrolines

The five-membered, nitrogen-containing pyrroline ring is a privileged structure. This ring is present in many bioactive compounds from natural sources. Pyrrolines-the dihydro derivatives of pyrroles-have three structural isomer classes, depending on the location of the double bond: 1-pyrrolines (3,4-dihydro-2H-pyrroles), 2-pyrrolines (2,3-dihydro-1H-pyrroles) and 3-pyrrolines (2,5-dihydro-1H-pyrroles). This review aims to describe the latest advances for the synthesis of pyrrolines by transition metal-catalyzed cyclizations. Only reactions in which the pyrroline ring is formed by metal promotion are described. Transformations of the pyrroline ring in other heterocycles, and the structural manipulations of the pyrroline itself are not discussed. The review is organized into three parts, each covering the metal-mediated synthesis of the three pyrroline isomers. Each part is subdivided according to the metal involved, and concludes with a brief description of notable biological activities within the class.

Diastereoselective synthesis of 1,3-disubstituted isoindolines and sultams via bronsted acid catalysis

Isoindolines and sultams formed under mild conditions.

Simple Indolizidine and Quinolizidine Alkaloids

This review of simple indolizidine and quinolizidine alkaloids (i.e., those in which the parent bicyclic systems are in general not embedded in polycyclic arrays) is an update of the previous coverage in Volume 55 of this series (2001). The present survey covers the literature from mid-1999 to the end of 2013; and in addition to aspects of the isolation, characterization, and biological activity of the alkaloids, much emphasis is placed on their total synthesis. A brief introduction to the topic is followed by an overview of relevant alkaloids from fungal and microbial sources, among them slaframine, cyclizidine, Steptomyces metabolites, and the pantocins. The important iminosugar alkaloids lentiginosine, steviamine, swainsonine, castanospermine, and related hydroxyindolizidines are dealt with in the subsequent section. The fourth and fifth sections cover metabolites from terrestrial plants. Pertinent plant alkaloids bearing alkyl, functionalized alkyl or alkenyl substituents include dendroprimine, anibamine, simple alkaloids belonging to the genera Prosopis, Elaeocarpus, Lycopodium, and Poranthera, and bicyclic alkaloids of the lupin family. Plant alkaloids bearing aryl or heteroaryl substituents include ipalbidine and analogs, secophenanthroindolizidine and secophenanthroquinolizidine alkaloids (among them septicine, julandine, and analogs), ficuseptine, lasubines, and other simple quinolizidines of the Lythraceae, the simple furyl-substituted Nuphar alkaloids, and a mixed quinolizidine-quinazoline alkaloid. The penultimate section of the review deals with the sizable group of simple indolizidine and quinolizidine alkaloids isolated from, or detected in, ants, mites, and terrestrial amphibians, and includes an overview of the "dietary hypothesis" for the origin of the amphibian metabolites. The final section surveys relevant alkaloids from marine sources, and includes clathryimines and analogs, stellettamides, the clavepictines and pictamine, and bis(quinolizidine) alkaloids.

Zirconium-catalyzed desymmetrization of aminodialkenes and aminodialkynes through enantioselective hydroamination

The catalytic addition of alkenes and amines (hydroamination) typically provides α- or β-amino stereocenters directly through C-N or C-H bond formation. Alternatively, desymmetrization reactions of symmetrical aminodialkenes or aminodialkynes provide access to stereogenic centers with the position controlled by the substrate's structure. In the present study of an enantioselective zirconium-catalyzed hydroamination, stereocenters resulting from C-N bond formation and desymmetrization of a prochiral quaternary center are independently controlled by the catalyst and reaction conditions. Using a single catalyst, the method provides selective access to either diastereomer of optically enriched five-, six-, and seven-membered cyclic amines from aminodialkenes and enantioselective synthesis of five-, six-, and seven-membered cyclic imines from aminodialkynes. Experiments on hydroamination of aminodialkenes testing the effects of the catalyst:substrate ratio, the absolute concentration of the catalyst, and the absolute initial concentration of the primary amine substrate show that the latter parameter strongly influences the stereoselectivity of the desymmetrization process, whereas the absolute configuration of the α-amino stereocenter generated by C-N bond formation is not affected by these parameters. Interestingly, isotopic substitution (H2NR vs D2NR) of the substrate enhances the stereoselectivity of the enantioselective and diastereoselective processes in aminodialkene cyclization and the peripheral stereocenter in aminodialkyne desymmetrization/cyclization.

Radical azidation reactions and their application in the synthesis of alkaloids

Recent advances in radical azidation using sulfonyl azides are presented. For instance, radical carboazidation using α-iodoketones, desulfitative carboazidation, and anti-Markovnikov hydroazidation of alkenes are described. These novel methods tolerate a large number of functional groups and allow the synthesis of organic azides that would be difficult to synthesize otherwise. The transformation of the azides using reductive processes as well as a Schmidt reaction under nonacidic conditions were used to synthesize alkaloids including indolizidine 167B, monomorine I, cylindricine C, and lepadiformine C.

Copper-catalyzed synthesis of N-fused heterocycles through regioselective 1,2-aminothiolation of 1,1-dibromoalkenes

The first aminothiolation of 1,1-dibromoalkene is described using an inexpensive copper/N,N-dimethylethylenediamine catalyst. The method provides a powerful means of using easily available 1,1-dihaloalkenes as precursors to fused heterocycles.