A wide range of acridones and their cyclo[b]‐fused derivatives are efficiently constructed by a double annulation of o‐enoyl arylisocyanides with α, β‐unsaturated carbonyls under simple metal‐free condition. This protocol is general, efficient and practical, featuring the successive formation of two rings by a one‐pot domino transformation. A tandem process involing an isocyanide‐based [1+4] cycloaddition, an aminofuran‐based intramolecular [4+2] cycloaddition, ring opening and aromatization is proposed for the transformation.
An efficient and regioselective palladium(II)‐catalyzed [5+2] annulation of unprotected o ‐indoloanilines with internal alkynes under microwave irradiation has been explored. The diverse imine‐containing 1,2‐fused indole[1,7‐a ]diazepines are constructed in moderate to excellent yields. The mechanistic pathway shows pivalic acid and molecular oxygen to play crucial roles for the regeneration of highly active electrophilic palladium species in the catalytic cycle.
A diastereoselective [4+2] annulation reaction between in situ generated p‐quinone methides and isatin‐derived enoates has been developed. In the presence of manganese dioxide as an oxidant, a variety of tosylaminophenyl‐substituted p‐quinone methide intermediates can be readily generated in an in situ fashion. Without pre‐preparation of p‐QMs, this unprecedented cascade reaction proceeds efficiently under mild conditions, providing a straightforward route to synthesize 4‐phenyl‐substituted tetrahydroquinolines bearing 3,3’‐spirooxindole scaffolds in good yields.
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
A facile and straightforward synthesis of benzoimidazo[2,1‐a]isoquinolines through Ru(II)‐catalyzed [4+2] annulation reaction of 2‐aryl benzimidazole and styrene has been explored. Tentative mechanistic studies imply the current reaction involves sequential C−C/C−N bond formation through the ortho C−H activation of 2‐aryl benzimidazole followed by C−N reductive elimination. This newly developed strategy is widely applicable and tolerates various 2‐arylbenzimidazole and vinyl derivatives, and allows the attractive vehicle for direct construction of diverse C6‐substituated benzoimidazoisoquinoline scaffold in good yields.
A direct and single‐step procedure towards substituted pyrimidine and pyridine derivatives via Lewis acid‐promoted [3+3] annulation between 3‐ethoxycyclobutanones and enamines or amidines is presented. Diverse substituted pyrimidine and pyridine derivatives were obtained in good to high yields with a wide substrate scope.
An unprecedented substrate‐dependent [5+1] annulation of 2‐isocyanochalcones with nitroalkanes was developed for the efficient synthesis of functionalized quinolines and 3‐nitrodihydroquinolines. This transformation delivers both the aromatic and dihydroquinolines by selectively elimination or retention of the nitro group. Moreover, 3‐nitroquinolines and tricyclic pyrrolo[2,3‐c]quinolines were conveniently constructed from the resulting 3‐nitrodihydroquinolines through a single operation, respectively.
A palladium‐catalyzed oxa‐[4+2] annulation of para ‐quinone methides with allyl carbonates bearing a nucleophilic alcohol side chain has been developed. This method provided an efficient strategy to the construction of 2‐oxaspiro‐cyclohexadienones via 1,6‐conjugated addition‐mediated allylation in moderate to good yields. Preliminary results on asymmetric derivatives promised potential in the synthesis of enantioenriched frameworks.
A highly efficient phosphine‐catalyzed [4+2] annulation of electron‐deficient diene and alkyl vinyl ketone was developed for the first time, which provides an easy access to functionalized cyclohexenes. This method has the advantages of mild reaction conditions, widely functional group tolerance, high yields and transition metal free.
An efficient [2+2] annulation strategy that isothiourea catalyst homobenzotetramisole (HBTM)‐catalyzed Mannich/lactamization cascade reaction of carboxylic acids with isatin‐derived ketimines has been disclosed. This protocol affords a range of structurally diverse spirooxindole β‐lactams bearing two vicinal stereogenic centers in good to high yields with good to excellent stereoselectivities.
A Lewis‐acid promoted chemoselective condensation of 2‐aminobenzimidazoles or 3‐aminoindazoles with 3‐ethoxycyclobutanones is presented. Diverse fused heterocycles benzo[4,5]‐imidazo[1,2‐a]pyrimidine and pyrimido[1,2‐b]‐indazole derivatives were obtained in moderate to high yields under mild conditions, the reaction mechanism of which was in sharp contrast to previous [3+3] annulation reaction of 3‐ethoxycyclobutanones.
An unprecedented copper(II) trifluoromethanesulfonate‐catalyzed [4+2] cascade annulation of propargylic alcohols with benzo[d ]isoxazoles proceeds through a sequential ring opening/Meyer–Schuster rearrangement/intermolecular cyclization. This protocol, which tolerates a broad variety of functional groups, offers a versatile, modular and atom‐economical access to a new class of fascinating quinoline derivatives in good yields under mild conditions. The transformation could be scaled up to a gram scale efficiently, thus highlighting the synthetic utility of this methodology.
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.
A formal sequential [1+2]‐ and [2+3]‐annulation of prop‐2‐ynylsulfonium salts and tosylaminomethyl enones was developed, constructing a series of methylene azabicyclo[3.1.0]hexane derivatives. A one‐pot procedure was established via hydration of an enamine intermediate to afford substituted cyclopropanes. Prop‐2‐ynylsulfonium salts acted as both C2 and C1 synthons in these two processes.
The first example of CoCl2‐catalyzed formal [5+2] oxidative annulation of o‐arylanilines with alkynes was developed, giving access to various important imine‐containing dibenzo‐[b,d]azepine scaffolds through sequential C−C/C−N bond formation. The reaction employs catalytic amount of manganese and oxygen as cooxidants, and features a broad substrate scope. Preliminary mechanistic studies suggested that C−H activation is involved in the rate‐determining step. Moreover, both internal and terminal alkynes are well tolerated in this transformation. Besides, a regioselective migratory insertion was observed when using terminal alkynes as substrates.
Herein, an efficient and regioselective Rh(III)‐catalyzed [4+2] annulation/lactonization cascade of indoles with 4‐hydroxy‐2‐alkynoates at room temperature to access the furo[3′,4′:4,5]pyrimido[1,6‐a]indole‐1,5(3H,4H)‐diones is described. This method features mild reaction conditions, operational simplicity, excellent regioselectivity, broad substrate scope with good functional group tolerance, and good to excellent yields.
A [4+2] annulation reaction of 1,3,5‐triazinanes and aurone‐derived α,β‐unsaturated imines has been developed, which enables the synthesis of 1,2,3,4‐tetrahydrobenzofuro[3,2‐d]pyrimidines under thermal conditions in high yields. This protocol is catalyst‐free and additive‐free.
