The first highly enantioselective formal [4+2] tandem cyclizations between isatylidenemalononitriles and activated dienes catalyzed by bifunctional chiral phosphine catalysts have been developed, yielding multistereogenic spirocyclic oxindoles in high yields and excellent optical purity. This reaction is accomplished via a tandem Rauhut–Currier/Michael/Rauhut–Currier reaction sequence.
An efficient method for the annulation of five‐ and six‐membered rings onto α,β‐enones is described via gold‐catalyzed 5‐ and 6‐exo‐dig selective cyclizations of alkynyl silyl enol ethers. 相似文献
The first catalytic asymmetric [3+2] cycloaddition of 2‐indolylmethanols with 3‐vinylindoles has been established, which makes use of C‐3 unsubstituted 2‐indolylmethanol as a C3 building block in the presence of a chiral phosphoric acid. By using this strategy, biologically important cyclopenta[b]indole frameworks were efficiently constructed with regiospecificity in high yields (up to 99%), excellent diastereo‐ and enantioselectivities (up to >95:5 dr, 96:4 er). This reaction not only represents the first catalytic asymmetric [3+2] cycloaddition of C‐3 unsubstituted 2‐indolylmethanols, but also has confronted the great challenges in 2‐indolylmethanol‐involved enantioselective transformations.
A tyrosine‐derived imidazolidin‐4‐one was immobilized on a modified poly(ethylene glycol) and converted in situ into a soluble polymer‐supported catalyst for the enantioselective Diels–Alder cycloaddition of acrolein to 1,3‐cyclohexadiene (up to 92% ee) and 2,3‐dimethyl‐1,3‐butadiene (73% ee). Catalyst recycling (up to four cycles) was accompanied by some loss of the chemical efficiency and marginal erosion of the enantioselectivity. 相似文献
A novel asymmetric [4+2] annulation of vinyl ketones with oxindole‐derived α,β‐unsaturated imines has been developed in the presence of a multifunctional thiourea‐phosphine catalyst derived from a natural amino acid, providing the first phosphine‐catalyzed enantioselective synthesis of 2′,3′‐dihydro‐1′H‐spiro[indoline‐3,4′‐pyridin]‐2‐ones in good yields with excellent stereoselectivities under mild conditions.
We report a radical cation [4+2] annulation of arylalkenes to afford naphthalene derivatives using an organic photosensitizer (9‐mesityl‐10‐methylacridinium perchlorate) under visible light photocatalysis. In the presence of oxygen (in the air), the oxidative dimerization/intramolecular [4+2] cycloaddition of two alkene molecules provides 3,4‐dihydronaphthalen‐1(2H)‐ones in good to high yields. Under a nitrogen atmosphere, (dihydro)naphthalenes were attained in moderate to excellent yields by using Selectfluor as the oxidant. The transformation proceeds via a tandem dimeric electrophilic addition/Friedel–Crafts cyclization/radical coupling/elimination sequence. This approach represents a mild and straightforward assembly of the naphthalene skeleton using a visible light photocatalytic cascade strategy.
The first highly enantioselective intramolecular N−H bond insertion was realized by using copper catalysts modified with chiral spirobisoxazoline ligands, which provides a novel strategy for the synthesis of chiral 2‐carboxytetrahydroquinolines. This reaction features fast reaction rate, high yield, high enantioselectivity, and mild reaction conditions.
The first copper(I)‐catalyzed asymmetric 1,3‐dipolar [3+4] cycloaddition of nitrones with azoalkenes has been developed, affording a variety of biologically important 1,2,4,5‐oxatriazepane derivatives in good yields with exclusive regioselectivities and excellent enantioselectivities.
The [2+2]‐cycloaddition reaction between ethyl glyoxylate and trimethylsilylketene is reported. Enantiomeric excesses up to 83% have been achieved with the use of only 1.0 mol % of a previously unreported chiral imidazolidinone‐ligated dirhodium(II) carboxamidate catalyst. An extensive survey of chiral catalysts has shown that enantiocontrol for cycloaddition increases as the steric bulk of the ligand is increased. However, enantioselectivity is increased to 99% ee by the addition of 10 mol % of quinine as a co‐catalyst with a chiral dirhodium(II) azetidinone‐ligated catalyst, and there is a significant decrease in reaction time. 相似文献
Various imidazolium ionic liquids such as [Bmim]PF6, [Bmim]SbF6, [Bmim]OTf and [Bmim]BF4 were screened for recycling an organic catalyst [(5S)‐5‐benzyl‐2,2,3‐trimethylimidazolidin‐4‐one ( 1 )] for asymmetric Diels–Alder reactions. Good yields and enantioselectivies (up to 85% yield and 93% ee) were obtained from reactions in [Bmim]PF6 or [Bmim]SbF6. However, reactions in [Bmim]OTf or [Bmim]BF4 gave racemic products in low yields. Isolation of the products by simple extraction using diethyl ether allowed recycling of the ionic liquid containing the immobilized catalyst in subsequent reactions without significant decrease of yields and enantioselectivities. 相似文献
An unprecedented copper(II)‐catalyzed enantioselective 1,3‐dipolar [3+4] cycloaddition of azomethine imines with in situ formed azoalkenes has been realized. This strategy provides a facile access to biologically important 1,2,4,5‐tetrazepine derivatives in high yield with exclusive regioselectivity and high stereoselectivity. Moreover, enantioenriched azomethine imines could be obtained via an efficient kinetic resolution using the same approach.
A new [3+2] cycloaddition strategy for the direct synthesis of highly substituted pyrroles from the readily available α‐acylketene dithioacetals (or related substrates) and commercially available propargylamines under mild metal‐free conditions has been developed. In this reaction, the acyl group plays a critical role in driving the conjugate addition of propargylamine and further cyclization to give pyrroles. Furthermore, the wide scope was confirmed by the preparation of 1,2,3,4‐tetrasubstituted pyrroles (60–70% yields) via a formal 1,2‐acyl migrating [3+2] cycloaddition pathway with N‐methylprop‐2‐yn‐1‐amine as the secondary amine component. 相似文献
A variety of substituted 2,2′‐bipyridines were synthesized by a 1,2‐bis(diphenylphosphino)ethane (dppe)/cobalt chloride hexahydrate (CoCl2⋅6 H2O)/zinc‐catalyzed [2+2+2] cycloaddition reaction of diynes and nitriles, with all reactions exhibiting exclusive regioselectivity. Thus, symmetrical and unsymmetrical 1,6‐diynes and 2‐cyanopyridine reacted in the presence of 5 mol % of dppe, 5 mol % of CoCl2⋅6 H2O and 10 mol % of zinc powder to provide the corresponding 2,2′‐bipyridines. Under identical reaction conditions, 1‐(2‐pyridyl)‐1,6‐diynes and nitriles reacted smoothly with exclusive regioselectivity to produce 2,2′‐bipyridines in good yield. 2,2′‐Bipyridines were also obtained by the double [2+2+2] cycloaddition reaction of 1,6,8,13‐tetraynes with nitriles. Similarly, 2,2′:6′,2′′‐terpyridines were synthesized from 1‐(2‐pyridyl)‐1,6‐diyne and 2‐cyanopyridine. The regiochemistry observed can be explained by considering the electronic nature of cobaltacyclopentadiene intermediates and nitriles. A survey of the exclusive regiochemical trend gives reasonable credence to the synthetic potential of the present method. 相似文献
A facile enantioselective synthesis of chiral pyrazolidines via a [3+2] cycloaddition reaction, involving a BINOL‐derived phosphoric acid and an in situ generated BINOL phosphate‐derived silicon Lewis acid, which may act cooperatively, has been developed. 相似文献
The reaction of nitriles with alkenyldiazo compounds in the presence of gold catalysts provides functionalized pyrrole derivatives in moderate to high yields. This formal [3+2] cyclization reaction takes place with complete regioselectivity. The observed regiochemical outcome suggests the attack of the nitrile to the terminal position of the alkenylgold carbenoid (vinylogous reactivity). A broad range of nitriles (including those bearing functional groups) is compatible with this cyclization reaction. 相似文献
Various 3‐azabicyclo[3.1.1]heptane derivatives were synthesized from Morita–Baylis–Hillman adduct‐derived 1,3‐dienes bearing a 4,4‐diaryl moiety through a thermal intramolecular [2+2] cycloaddition approach. By using the same approach, bicyclo[3.1.1]heptane, 3‐azabicyclo[3.2.0]heptane, and 3‐oxabicyclo[3.1.1]heptane derivatives could also be synthesized. A structurally similar dimethylallyl derivative underwent an intramolecular ene reaction to afford the pyrrolidine derivative.
An organocatalytic asymmetric formal [3+3] cycloaddition reaction of α,β‐unsaturated aldehydes with Nazarov reagents promoted by prolinol derivatives afforded, after oxidation, 3,4‐dihydropyranones in good yields with high enantioselectivities of up to 97% ee. 相似文献
The stereoselective synthesis of trans‐annelated pyrano[3,2‐c]benzopyrans has been achieved by intramolecular [4+2] cycloaddition of o‐benzoquinone methides that are generated in situ from o‐hydroxybenzaldehydes and unsaturated alcohols using an air‐ and moisture‐stable ionic liquid, i.e., 1‐butyl‐3‐methylimidazolium tetrafluoroborate [bmim]BF4 under mild and neutral conditions. 相似文献
With the use of a bifunctional chiral phosphine as the catalyst, the asymmetric [3+2] annulation of Morita–Baylis–Hillman carbonates with cyclic 1‐azadienes proceeded smoothly under mild conditions to give various enantiomerically enriched cyclopentene derivatives bearing three consecutive tertiary stereocenters and a sulfamate moiety in moderate to excellent yields with moderate to excellent enantioselectivities and excellent diastereoselectivities.
A highly efficient and enantioselective inverse electron‐demand hetero‐Diels–Alder reaction of in situ generated 1,2‐diaza‐1,3‐dienes with enol ethers has been developed with the use of a chiral copper/bisoxazoline complex as the catalyst. The reaction exhibits high enantioselectivity (up to 90% ee) and provides a robust and powerful method to synthesize a variety of structurally diverse and densely substituted chiral pyridazine derivatives in good to excellent yields.