Gold(I)-catalyzed synthesis of γ-hydroxyketones from 5-allyloxy-1-ynes

The Au(I)-catalyzed reactions of 5-allyloxy-1-ynes gave various γ-hydroxyketones, via a hydration-terminated domino sequence involving sigmatropic allyl migration as the key event. Moreover, the scope of the sigmatropic allyl transfer was systematically determined.     

Synthesis of 4H-chromenes by silver(Ⅰ)-catalyzed cycloaddition of ortho-quinone methides with N-allenamides

Chromenes represent an important class of six-membered heterocycles and have drawn tremendous attention in recent years. In this article, we report a convenient and practical synthesis of this heterocycle by a silver(I)-catalyzed cycloaddition reaction between in situ generated ortho-quinone methides and N-allenamides. Diverse 4H-chromenes were synthesized in good to excellent yields under very mild conditions.     

Magnetically recyclable Cu-BTC@Fe3O4-catalyzed synthesis of aryl α-chlorobenzyl ketones

Metal–organic framework (MOF) composite, viz. Cu-BTC@Fe₃O₄ (BTC is 1,3,5-benzenetricarboxylate), was prepared and utilized for the synthesis of aryl α-chlorobenzyl ketones from arenediazonium salts and arylacetylenes in moderate to good yields. This reaction proceeded via a radical domino process. The catalyst could be readily recovered with an external permanent magnet, with slight decrease in its activity after successive six runs.     

Cu(OTf)2-catalyzed synthesis of highly substituted 1-methoxy imidazoles via (3 + 2) cycloaddition between imino carbenoids and nitriles

A Cu(OTf)₂-catalyzed simple synthetic approach for highly substituted 1-alkoxy imidazole has been described. This protocol involves (3 + 2) cycloaddition of oximino carbenoids with organo nitriles. This method has wide substrate scope and tolerates alkyl, aryl, substituted aryl, vinyl, and ester nitriles.     

Rh(I)-catalyzed [5+1] cycloaddition of vinylcyclopropanes and CO for the synthesis of α,β- and β,γ-cyclohexenones

A cationic Rh(I)-catalyzed [5 + 1] cycloaddition of vinylcyclopropanes and CO has been developed, affording either β,γ-cyclohexenones as major products or α,β-cyclohexenones exclusively, under different reaction conditions.     

Facile photochemical synthesis of α-ketoamides and quinoxalines from amines and benzoylacetonitrile under mild conditions

A selective protocol for the synthesis of either α-ketoamides or quinoxaline derivatives under the same reaction conditions has been achieved simply by varying substitution number of amino-groups. The method features metal-free, room temperature and broad substrate scopes as well as no extra oxidant. This process applies to various substituent groups and gives products in moderate to good yield. Finally, a rational mechanism was proposed.     

Regio- and stereoselective synthesis of 3- and 5-(C-glycosyl)-4-nitroisoxazolidines by nitrone–nitroalkene [3+2] cycloaddition reactions

Cycloaddition reactions of nitrones, including sugar nitrones, with nitroalkenes, including sugar nitroolefins, led with complete regioselectivity and stereospecificity to 4,5-trans-4-nitroisoxazolidines in 51–78% global yields. The endo/exo stereoselectivity depends on the type of sugar derivative used. As expected, the best π-diastereofacial selectivity was observed when both partners were sugar derivatives. Isomerisation of the first formed diastereomers by the action of silica gel was observed in some cases. Absolute configurations for two crystalline products were assigned by X-ray diffraction methods.     

OsO4-catalyzed amination of silyl enol ethers: enantioselective synthesis of α-amino ketones

Osmium tetroxide catalyzed asymmetric aminohydroxylation of silyl enol ethers using cinchona alkaloids as chiral ligands and chloramine-T as the nitrogen source affords enantiomerically pure α-amino ketones.     

Au(III)-catalyzed tandem amination-hydration of alkynes: synthesis of α-(N-2-pyridonyl)ketones

A new Au(III)-catalyzed tandem amination-hydration reaction has been discovered, leading to the formation of α-(N-2-pyridonyl)ketones and heterocyclic analogues in good to excellent yields (14 examples, 48-90%). This reaction demonstrates the unusual use of a heterocyclic sp(2) nitrogen nucleophile in a gold-catalyzed 6-endo-dig cyclization. The tandem process allows rapid access to α-(N-2-pyridonyl)ketones, making them a convenient building block for the synthesis of more complex N-alkyl pyridone targets.     

Cu(II)-catalyzed enantioselective 1,3-dipolar cycloaddition of nitrones with α, β-unsaturated acyl phosphonates

A highly enantioselective 1, 3-dipolar cycloaddition of nitrone with α, β-unsaturated acyl phosphonate was developed for the first time by using a chiral indane-bis(oxazoline)-copper(II) complex. The reaction proceeded smoothly under mild conditions to provide isoxazolidines with multi-stereocenters in good yields with high to excellent diastereo- (>20:1 dr) and enantioselectivities (up to 99% ee). The resulting products were readily converted to multi-functional isoxazolidines or γ-amino alcohol compounds.     

Synthesis of functionalized α-CF3-α-aminophosphonates via Cu(I)-catalyzed 1,3-dipolar cycloaddition

A convenient method for the preparation of α-CF₃-α-aminophosphonates bearing alkynyl group at the α-carbon atom has been described. New alkynylphosphonates have been further utilized in the synthesis of functionalized triazole-containing α-CF₃-α-aminophosphonates via copper-catalyzed (3+2)-cycloaddition to different organic azides.     

Iron(III)-catalyzed synthesis of selenoesters from α-amino carbonyl derivatives at room temperature

An Fe(III)-catalyzed efficient method has been developed for the synthesis of selenoester derivatives in high yields through the coupling of α-amino carbonyl/glycine derivatives and diselenides under ambient air. A library of benzoselenoate derivatives having a variety of substituents has been synthesized. A plausible reaction pathway has been predicted. Experimental results suggest that the reaction proceeds through a radical pathway. Operational simplicity, compatibility with various α-amino carbonyls and diselenides, high yields, fast reaction and mild reaction conditions are the notable advantages of this procedure. We have also shown the practical application of the synthesized selenoesters which is useful to generate peptide bonds in biological sciences.     

Rh(III)-catalyzed annulation of azobenzenes and α-Cl ketones toward 3-acyl-2H-indazoles

Rhodium(III)-catalyzed [4 + 1] cyclization of azobenzenes with α-Cl ketones has been developed. 3-Acyl-2H-indazoles could be easily afforded in up to 97% yields for more than 30 examples. The obtained products are potentially valuable in organic synthesis and drug discovery. This protocol featured with high efficiency, extensive functional group tolerance and mild reaction conditions. The one-step efficient construction of an anti-inflammatory agent confirms the practicability of this procedure.     

Asymmetric synthesis of 3-amino-β-lactamsvia Staudinger ketene-imine cycloaddition reaction (review)

Recent advances in asymmetric synthesis of 3-amino--lactamsvia Staudinger ketene-imine cycloaddition reaction are summarized.Departamento de Quimica Organica, Universidad del Pais Vasco. Facultad de Quimica, Apdo. 1072, 20080 San Sebastian, Spain. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1448–1462, November, 1998.     

Enantioselective synthesis of α-fluoro-β(3)-amino esters: synthesis of enantiopure, orthogonally protected α-fluoro-β(3)-lysine

The scope of a tandem conjugate addition-fluorination sequence performed on α,β-unsaturated esters using the enantiopure lithium amide derived from (S)-N-benzyl-N-(α-methylbenzyl)amine, and the electrophilic fluorinating agent N-fluorobenzenesulfonimide has been investigated. Using this method, α-fluoro-β(3)-amino esters can be obtained in up to quantitative yield and 80:20 to >99:1 dr. This simple methodology does not rely on the use of α-amino acids from the chiral pool and thus provides the potential for the preparation of enantiopure α-fluoro-β(3)-amino acids with a wide variety of side chains. Its utility was demonstrated through the synthesis of orthogonally protected (2S,3S)-α-fluoro-β(3)-lysine.     

Aerobic oxidation of β-dicarbonyls into vicinal tricarbonyls by Cu(II) salts for one-pot synthesis of quinoxalines

Vicinal tricarbonyl intermediates are directly synthesized from β-dicarbonyls with the aid of Cu(II) salts and air, and they are further condensed with phenylene diamine to produce a range of quinoxalines in moderate to good yields in one-pot reaction.     

Rhodium(I)-catalyzed [3+2] intramolecular cycloaddition of alkylidenecyclopropane–propargylic esters

An interesting rhodium(I)-catalyzed [3+2] intramolecular cycloaddition of alkylidenecyclopropanes 1 containing propargylic esters has been described in this context. A variety of bicyclo[3.3.0]octene derivatives were obtained in moderate to good yields under mild conditions. The alkylidenecyclopropane-enynes 2 could be also converted to the corresponding cycloadducts 3 in good yields.