Unusual Formal [1+4] Annulation through Tandem P(NMe2)3‐Mediated Cyclopropanation/Base‐Catalyzed Cyclopropane Rearrangement: Facile Syntheses of Cyclopentenimines and Cyclopentenones

An unusual formal [1+4] annulation of α‐dicarbonyl compounds with 1,1‐dicyano‐1,3‐dienes has been realized, leading to facile syntheses of cyclopentenimines and cyclopentenones in a unique manner. Mechanistic investigation implies that this reaction takes place through a P(NMe₂)₃‐mediated cyclopropanation followed by a base‐catalyzed cyclopropane rearrangement. It therefore represents an unprecedented [1+4] annulation mode involving Kukhtin–Ramirez adducts.     

Phosphine-Catalyzed Annulations between Modified Allylic Derivatives and Polar Dienes and Substituent Effect on the Annulation Mode

in this work, the phosphine-catalyzed annulation reactions between modified allylic derivatives and polar 1,1-dicyano-1,3-dienes have been studied. In the catalysis of PPh3 （20 mol%）, a [4 ＋ 1 ] annulation reaction is realized between a series of l,l-dicyano-2,4-diaryl-1,3-dienes and ethoxycarbonyl-activated allylic acetate, producing polysubstituted cyclopentenes in modest to excellent yields. It is also observed that the substituents of both 1,3-dienes and allylic derivatives have a significant influence on the annulation mode： under the catalysis of PPh3 or PBu3 （20 mol%）, regioselective [3 ＋ 2] annulation products are formed from differently substituted substratcs.     

Asymmetric Synthesis of Spiropyrazolones through Phosphine‐Catalyzed [4+1] Annulation

An enantioselective synthesis of spiropyrazolones from allenoate‐derived MBH acetates and pyrazolones through a phosphine‐mediated [4+1] annulation process has been developed. Spiropyrazolones were readily prepared in good chemical yields and good to high enantioselectivities. This is the first asymmetric example in which α‐substituted allenoates were utilized as a C₄ synthon for phosphine‐catalyzed [4+1] annulation.     

Phosphine‐Catalyzed Domino Reactions: A Route to Functionalized Bicyclic Skeletons

A novel strategy that involves phosphine‐catalyzed sequential [2+3] and [3+2] annulation reactions was developed. In this domino reaction, γ‐substituted allenoates were used as novel C₄ synthons, and the bicyclic cyclopenta[b]dihydrofuran derivatives were produced in good to excellent diastereoselectivities and yields under mild conditions. Furthermore, preliminary studies on an asymmetric variant of this reaction proceeded with moderate enantioselectivity.     

Facile Synthesis of Spirooxindole‐Cyclohexenes via Phosphine‐Catalyzed [4 + 2] Annulation of α‐Substituted Allenoates

A phosphine‐catalyzed [4 + 2] annulation of α ‐substituted allenoate with exocyclic alkene moiety of oxindoles or indan‐1,3‐diones has been developed. Thus, under the catalysis of PPh₃ (20 mol%), a series of spirooxindole‐ or spiroindan‐1,3‐dione‐cyclohexenes have been obtained in moderate to excellent yields and regioselectivity from the annulations of α ‐methyl allenoates with 3‐methyleneoxindoles or 2‐methyleneindan‐1,3‐diones. This method offers an easy access to structurally novel spirocyclohexenes.     

N‐Heterocyclic Carbene‐Catalyzed [2+2+2] Annulation of Allenoates with Trifluoromethylketones

In contrast with the reported phosphine‐ and DABCO‐catalyzed [3+2] and [2+2] annulation of allenoates with trifluoromethylketone, the [2+2+2] annulation of allenoates and two molecules of trifluoromethylketone was found under the condition of N‐heterocyclic carbene catalysis.     

Skeletal Rearrangement in the ZnII‐Catalyzed [4+2]‐Annulation of Disubstituted N‐Hydroxy Allenylamines with Nitrosoarenes to Yield Substituted 1,2‐Oxazinan‐3‐one Derivatives

This work reports zinc‐catalyzed [4+2]‐annulation reactions of disubstituted N‐hydroxy allenylamines with nitrosoarenes to afford substituted 1,2‐oxazinan‐3‐ones with a skeletal rearrangement. This annulation is applicable to a reasonable scope of allenylamines and nitrosoarenes. Our control experiments indicate that nitrosobenzene can also implement this annulation through a radical annulation path, but with poor efficiency. Zn(OTf)₂ or AgOTf greatly improves the efficiency of this [4+2]‐annulation; the effect of these metal species is discussed in detail.     

Enantioselective Phosphine‐Catalyzed Formal [4+4] Annulation of α,β‐Unsaturated Imines and Allene Ketones: Construction of Eight‐Membered Rings

The first highly enantioselective phosphine‐catalyzed formal [4+4] annulation has been developed. In the presence of amino‐acid‐derived phosphines, the unprecedented [4+4] annulations between benzofuran/indole‐derived α,β‐unsaturated imines and allene ketones proceeded smoothly, thus affording azocines, bearing either a benzofuran or an indole moiety, in excellent yields and with nearly perfect enantioselectivities (≥98 % ee in most cases). This work marks the first efficient asymmetric construction of optically enriched eight‐membered rings by phosphine catalysis.     

Asymmetric [3+2] annulation of allenes with maleimides catalyzed by dipeptide-derived phosphines: facile creation of functionalized bicyclic cyclopentenes containing two tertiary stereogenic centers

D-Threonine-L-tert-leucine-derived bifunctional phosphine, Cat. 11, catalyzed highly enantioselective [3+2] annulation of maleimides with allenes has been disclosed, allowing the synthesis of optically active functionalized bicyclic cyclopentenes containing two tertiary stereogenic centers in good to high yields along with good to high enantioselectivities.     

Rhodium(III)‐Catalyzed [3+2]/[5+2] Annulation of 4‐Aryl 1,2,3‐Triazoles with Internal Alkynes through Dual C(sp2)H Functionalization

A rhodium(III)‐catalyzed [3+2]/[5+2] annulation of 4‐aryl 1‐tosyl‐1,2,3‐triazoles with internal alkynes is presented. This transformation provides straightforward access to indeno[1,7‐cd]azepine architectures through a sequence involving the formation of a rhodium(III) azavinyl carbene, dual C(sp²)? H functionalization, and [3+2]/[5+2] annulation.     

Synthesis of new 5‐acetyl(arylmethyliden)‐4‐thiazolidones

A new approach to the synthesis of new heterocyclic compounds with triazine and 4‐thiazolidone fragments in one molecule is developed. The synthesis methods comprise [2+3]‐cyclocondensation reactions essential in the preparative synthesis of 4‐thiazolidone derivatives. The reactions of S,N‐nucleophiles with C₂‐cyclization agents for the synthesis of a number of biologically active 2‐triazin‐4‐thiazolidones were investigated. The interaction of thiosemicarbazone of sym‐triazine with derivatives of α‐halogencarboxylic acids and maleic anhydride resulted in correspondent (2‐[2‐(4,6‐dichloro‐1,3,5‐triazin‐2‐yl)hydrazino]‐5‐(3,4,5‐ R‐p‐phenyl‐methyliden)‐1,3‐thiazol‐4‐ones obtained in the one‐step synthesis. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 21:392–396, 2010; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20631     

Phosphine‐Initiated Domino Reaction: A Convenient Method for the Preparation of Spirocyclopentanones

An efficient synthetic approach has been developed for the construction of the spirocyclopentanone skeleton via a phosphine‐catalyzed [3+2] annulation reaction. With this novel and economical protocol, various quaternary carbon‐centered spirocyclopentanones could be readily obtained.     

A Cooperative N‐Heterocyclic Carbene/Chiral Phosphate Catalysis System for Allenolate Annulations

The highly enantioselective NHC‐catalyzed [3+2] annulation reaction with α,β‐alkynals and α‐ketoesters has been developed. A new mode of cooperative catalysis involving the combination of a chiral Brønsted acid and a C₁‐symmetric biaryl saturated‐imidazolium precatalyst was required to generate the desired γ‐crotonolactones in high yields and levels of enantioselectivity.     

A one‐dimensional zinc(II) coordination polymer incorporating [1,1′‐biphenyl]‐4,4′‐dicarboxylate and N,N′‐bis(pyridin‐3‐ylmethyl)‐[1,1′‐biphenyl]‐4,4′‐dicarboxamide ligands

In the title compound, catena‐poly[[[N,N′‐bis(pyridin‐3‐ylmethyl)‐[1,1′‐biphenyl]‐4,4′‐dicarboxamide]chloridozinc(II)]‐μ‐[1,1′‐biphenyl]‐4,4′‐dicarboxylato‐[[N,N′‐bis(pyridin‐3‐ylmethyl)‐[1,1′‐biphenyl]‐4,4′‐dicarboxamide]chloridozinc(II)]‐μ‐[N,N′‐bis(pyridin‐3‐ylmethyl)‐[1,1′‐biphenyl]‐4,4′‐dicarboxamide]], [Zn₂(C₁₄H₈O₄)Cl₂(C₂₆H₂₂N₄O₂)₃]_n, the Zn^II centre is four‐coordinate and approximately tetrahedral, bonding to one carboxylate O atom from a bidentate bridging dianionic [1,1′‐biphenyl]‐4,4′‐dicarboxylate ligand, to two pyridine N atoms from two N,N′‐bis(pyridin‐3‐ylmethyl)‐[1,1′‐biphenyl]‐4,4′‐dicarboxamide ligands and to one chloride ligand. The pyridyl ligands exhibit bidentate bridging and monodentate terminal coordination modes. The bidentate bridging pyridyl ligand and the bridging [1,1′‐biphenyl]‐4,4′‐dicarboxylate ligand both lie on special positions, with inversion centres at the mid‐points of their central C—C bonds. These bridging groups link the Zn^II centres into a one‐dimensional tape structure that propagates along the crystallographic b direction. The tapes are interlinked into a two‐dimensional layer in the ab plane through N—H...O hydrogen bonds between the monodentate ligands. In addition, the thermal stability and solid‐state photoluminescence properties of the title compound are reported.     

Divergent Reactivity in Palladium‐Catalyzed Annulation with Diarylamines and α,β‐Unsaturated Acids: Direct Access to Substituted 2‐Quinolinones and Indoles

A palladium‐catalyzed C?H activation strategy has been successfully employed for exclusive synthesis of a variety of 3‐substituted indoles. A [3+3] annulation for synthesizing substituted 2‐quinolinones was recently developed by reaction of α,β‐unsaturated carboxylic acids with diarylamines under acidic conditions. In the present work, an analogous [3+2] annulation is achieved from the same set of starting materials under basic conditions to generate 1,3‐disubstituted indoles exclusively. Mechanistic studies revealed an ortho‐palladation–π‐coordination–β‐migratory insertion–β‐hydride elimination reaction sequence to be operative under the reaction conditions.     

Expanding the Scope of Enantioselective FerroPHANE‐Promoted [3+2] Annulations with α,β‐Unsaturated Ketones

The planar chiral 2‐phospha[3]ferrocenophane I has been shown to be the first efficient nucleophilic organocatalyst for the enantioselective synthesis of cyclopentenylphosphonates, through [3+2] cyclizations between diethyl allenylphosphonate and α,β‐unsaturated ketones. The same catalyst has also been applied to the highly enantioselective [3+2] cyclizations of allenic esters with dibenzylideneacetone and analogous bis‐enones, leading to functionalised cyclopentenes with either monocyclic or spirocyclic structures (ee 84–95 %). It has been shown that the residual enone functions in the resulting cyclopentenes can be involved in subsequent cyclization steps to afford unprecedented C₂‐symmetric bis‐cyclopentenylketones. In order to provide insight into the behaviour of FerroPHANE I as a chiral catalyst in [3+2] cyclisations, the energetically most favoured isomers of the key phosphine‐allene adduct have been calculated by DFT methods. Factors likely to control the chiral induction process are highlighted.     

Nickel(0)‐Catalyzed Enantioselective Annulations of Alkynes and Arylenoates Enabled by a Chiral NHC Ligand: Efficient Access to Cyclopentenones

Cyclopentenones are versatile structural motifs of natural products as well as reactive synthetic intermediates. The nickel‐catalyzed reductive [3+2] cycloaddition of α,β‐unsaturated aromatic esters and alkynes constitutes an efficient method for their synthesis. Here, nickel(0) catalysts comprising a chiral bulky C₁‐symmetric N‐heterocyclic carbene ligand were shown to enable an efficient asymmetric synthesis of cyclopentenones from mesityl enoates and internal alkynes under mild conditions. The bulky NHC ligand provided the cyclopentenone products in very high enantioselectivity and led to a regioselective incorporation of unsymmetrically substituted alkynes.     

Poly[nickel(II)‐di‐μ‐4,4′‐bipyridyl‐κ4N:N′‐μ‐dichromato‐κ2O:O′] and poly[copper(II)‐di‐μ‐4,4'‐bipyridyl‐κ4N:N′‐μ‐dichromato‐κ2O:O′]

The novel title hybrid isomorphous organic–inorganic mixed‐metal dichromates, [Ni(Cr₂O₇)(C₁₀H₈N₂)₂] and [Cu(Cr₂O₇)(C₁₀H₈N₂)₂], have been synthesized. A non‐centrosymmetric three‐dimensional (4,6)‐net is formed from a linear chain of vertex‐linked [Cr₂O]²⁻ and [MN₄O]²⁺ (M = Ni and Cu) units, which in turn are linked by the planar bidentate 4,4′‐­bipyridine ligand through the four remaining vertices of the [MN₄O]²⁺ octahedra. There are two such three‐dimensional nets that interpenetrate with inversion symmetry.     

Dearomatization of 3‐Nitroindoles by a Phosphine‐Catalyzed Enantioselective [3+2] Annulation Reaction

The dearomatization of 3‐nitroindoles through a chiral‐phosphine‐mediated [3+2] annulation reaction is described. This method makes use of readily available 3‐nitroindoles as an aromatic feedstock and rapidly delivers a wide range of cyclopentaindoline alkaloid scaffolds in a highly enantioselective manner. Notably, phosphine‐triggered cyclization has not been utilized previously in a dearomatization process.     

Rhodium(III)‐Catalyzed [3+2] Annulation of 5‐Aryl‐2,3‐dihydro‐1H‐pyrroles with Internal Alkynes through C(sp2)H/Alkene Functionalization

This study describes a new rhodium(III)‐catalyzed [3+2] annulation of 5‐aryl‐2,3‐dihydro‐1H‐pyrroles with internal alkynes using a Cu(OAc)₂ oxidant for building a spirocyclic ring system, which includes the functionalization of an aryl C(sp²)? H bond and addition/protonolysis of an alkene C?C bond. This method is applicable to a wide range of 5‐aryl‐2,3‐dihydro‐1H‐pyrroles and internal alkynes, and results in the assembly of the spiro[indene‐1,2′‐pyrrolidine] architectures in good yields with excellent regioselectivities.