One‐Pot,Four‐Component Synthesis of Novel Spiro[indeno[2,1‐b]quinoxaline‐11,4′‐pyran]‐2′‐amines

A one‐pot, four‐component reaction for the efficient synthesis of novel spiro[indeno[2,1‐b]quinoxaline‐11,4′‐pyran]‐2′‐amines by using InCl₃ is described. The syntheses are achieved by reacting ninhydrin with 1,2‐diaminobenzenes to give indenoquinoxalines, which are trapped in situ by alkyl malonates and various α‐methylencarbonyl compounds through cyclization, providing multifunctionalized spiro‐substituted indeno[2,1‐b]quinoxaline‐11,4′‐pyran‐2′‐amines.     

1‐Bromo‐2‐(cyclopropylidenemethyl)benzene: A Useful Building Block in the Palladium‐Catalyzed Reaction of 2‐Alkynylbenzenamine

A novel palladium‐catalyzed domino reaction of 1‐bromo‐2‐(cyclopropylidenemethyl)benzene and 2‐alkynylbenzenamine is reported, which generates 2‐(naphthalen‐2‐yl)benzenamines and 5H‐indeno[1,2‐c]quinolines via 6‐endo and 5‐exo cyclization, respectively. The regioselectivity for the final outcome can be affected by phosphine and N‐heterocyclic carbene ligands.     

Efficient synthesis and spectral determination of 11‐[(o‐ m‐ and p‐substituted)‐phenyl]‐8‐chloro‐3,3‐dimethyl‐2,3,4,5,10,11‐hexahydro‐1H‐dibenzo[b,e][1,4]diazepin‐1‐ones

A new synthesis to obtain eleven novel derivatives of 11‐[(o‐ m‐ and p‐substituted)‐phenyl]‐8‐chloro‐3,3‐dimethyl‐2,3,4,5,10,11‐hexahydro‐1H‐dibenzo[b,e][1,4]diazepin‐1‐ones with possible pharmacological activity in the central nervous system in two efficient steps has been developed. The final products were obtained by condensation and cyclization between 3‐[4‐chloro‐1,2‐phenylenediamine]‐5,5‐dimethyl‐2‐cyclohexenone with (o‐ m‐ and p‐substituted)benzaldehyde. The structure of all products was corroborated by ir, ¹H‐nmr, ¹³C‐nmr and high resolution in ms.     

Mechanistic Understanding of the Divergent Cyclizations of o‐Alkynylbenzaldehyde Acetals and Thioacetals Catalyzed by Metal Halides

The mechanisms of regiodivergent cyclizations of o‐alkynylbenzaldehyde acetals and thioacetals catalyzed by Pd and Pt halides are studied. DFT calculations found that both reactions are initiated by electrophilic activation of the acetylenic moiety instead of the previously proposed metal‐triggered C?X (X=O, S) cleavage. Both the regioselective cyclization of the π‐alkyne complex and the chemoselective [1,2]‐migration in the carbenoid intermediate were determined as key steps to achieving the observed divergence. For acetal derivatives containing an internal alkyne, the 6‐endo‐dig cyclization is more favorable and leads to the carbenoid intermediate easily through further steps of C?X fragmentation and carbocation cyclization. Then, from the carbenoid intermediate, the [1,2]‐migration of sulfur is easier than that of H, Me, and Ph; whereas, a reversed aptitude was predicted for the oxygen analogue, which is consistent with the greater ability of sulfur atoms to stabilize β‐carbocations. However, for precursors containing a terminal alkyne, the 5‐exo‐dig pathway is preferred and only the 1,2‐disubstituted indene product is seen, irrespective of the nature of the acetal; thus, a different product from that reported in the literature is predicted for benzaldehyde acetal with a terminal alkyne at the ortho position. This prediction led us to reconsider some of the reported results and hidden realities were uncovered with solid new experimental evidence.     

Diversity‐Oriented Synthesis of Novel 2′‐Aminospiro[11H‐indeno[1,2‐b]quinoxaline‐11,4′‐[4H]pyran] Derivatives via a One‐Pot Four‐Component Reaction

A sequential one‐pot four‐component reaction for the efficient synthesis of novel 2′‐aminospiro[11H‐indeno[1,2‐b]quinoxaline‐11,4′‐[4H]pyran] derivatives 5 in the presence of AcONH₄ as a neutral, inexpensive, and dually activating catalyst is described (Scheme 1). The syntheses are achieved by reacting ninhydrin ( 1 ) with benzene‐1,2‐diamines 2 to give indenoquinoxalines, which are trapped in situ by malono derivatives 2 and various α‐methylenecarbonyl compounds 4 through cyclization, providing the multifunctionalized 2′‐aminospiro[11H‐indeno[1,2‐b]quinoxaline‐11,4′‐[4H]pyran] analogs 5 . This chemistry provides an efficient and promising synthetic way of proceeding for the diversity‐oriented construction of the spiro[indenoquinoxalino‐pyran] skeleton.     

Synthesis and Antimicrobial Activity of Some 1,3‐Disubstituted Indeno[1,2‐c]pyrazoles

Synthesis of new 3‐alkyl indeno[1,2‐c]pyrazoles, possessing 4‐substituted thiazole moiety at position‐1 derived from 2‐acyl indane‐1,3‐diones, has been described. These compounds and their precursor were screened for their antibacterial (Staphylococcus aureus, Bacillus subtilis, Escherichia coli) and antifungal (Aspergillus niger, Candida albicans) activities.     

The preparation of benzoisothiazolo[1,2‐b][1,2]isoquinolin‐11‐one‐1,1‐dioxides from dilithiated ortho‐toluic acids and lithiated methyl 2‐(aminosulfonyl)benzoate

Select dilithiated ortho‐toluic acids were prepared in excess lithium diisopropylamide and condensed with methyl 2‐(aminosulfonyl)benzoate followed by a twofold cyclization of intermediates to afford benzoisothiazolo[1,2‐b][1,2]isoquinolin‐11‐one‐1,1‐dioxides, a new fused‐ring heterocyclic system.     

Some Reactions with Indane‐1,3‐dione: A Facile Synthesis of Pentacycline Heterocyclic Analogues

Indane‐1,3‐dione 1 reacts with salicylaldehyde 5 and malononitrile 3 to afford 6‐amino‐7‐imino‐7H‐indeno‐[2′,1′:5,6]‐pyrano‐[3,4 ‐ c]‐chromene 6 , which could be transformed into the corresponding 7‐oxo derivative 7 . 2‐(3‐Oxoindan‐1‐ylidene)‐malononitrile 10 couples with the diazonium salts 8 , 14 , and 15 to afford after cyclization the indeno‐[2,1‐c]‐pyridazine 13 and the indeno‐[2′,1′:3,4]‐pyridazino‐[1,6‐a]‐quinazoline derivatives 20 and 21 , respectively.     

A synthesis of new pyrrolo[3,2‐c]quinolines

A synthesis of pyrrolo[3,2‐c]quinolines substituted in the 7‐ and 8‐ positions by methoxy groups and in the 3‐ position by an amido group is described. The structures were designed to have a crescent shape, a planar fused cyclic moiety with two ortho methoxy groups and ionisable amino or amidinic group at pH 7.     

A New Four‐Component Reaction for the Synthesis of Spiro[4H‐indeno[1,2‐b]pyridine‐4,3′‐[3H]indoles]

A new four‐component synthesis of spiro[4H‐indeno[1,2‐b]pyridine‐4,3′‐[3H]indoles] and spiro[acenaphthylene‐1(2H),4′‐[4H‐indeno[1,2‐b]pyridines] by the reaction of indane‐1,3‐dione, 1,3‐dicarbonyl compounds, isatins (=1H‐indole‐2,3‐diones) or acenaphthylene‐1,2‐dione, and AcONH₄ in refluxing toluene in the presence of a catalytic amount of pyridine is reported.     

Synthesis of fused pyrimidines with N‐, S‐heterocyclic moieties by double‐annelation reaction

A variety of tri‐ and tetracyclic hetero systems were obtained by reaction of heteroaromatic ortho‐aminoesters or ortho‐aminonitriles with iminothioether, yielding double‐annelation of a thiazolo[3,2‐a]‐pyrimidine, pyrimido[2,l‐b]thiazine, imidazo[1,2‐a]pyrimidine, and pyrimido[1,2‐a]pyrimidine moieties in a one‐pot process.     

Regio‐ and Chemoselective N‐1 Acylation of Indoles: Pd‐Catalyzed Domino Cyclization to Afford 1,2‐Fused Tricyclic Indole Scaffolds

A concise method for the synthesis of 1,2‐fused tricyclic indole scaffolds by domino cyclization involving a Pd‐catalyzed Sonogashira coupling, indole cyclization, regio‐ and chemoselective N‐1 acylation, and 1,4‐Michael addition is reported. This method provides straightforward access to tetrahydro[1,4]diazepino[1,2‐a]indole and hexahydro[1,5]diazocino[1,2‐a]indole scaffolds.     

Insights into the Gold‐Catalyzed Propargyl Ester Rearrangement/Tandem Cyclization Sequence: Radical versus Gold Catalysis—Myers–Saito‐ versus Schmittel‐Type Cyclization

A detailed study of the gold‐catalyzed tandem 1,3‐carboxy migration/allene–enyne cycloisomerization was undertaken. It was found that after the initial allene formation the selectivity of the reaction is strongly influenced by the polarization of the remaining alkyne. Depending on the substitution pattern of the starting diynes, either a Schmittel‐ or a Myers–Saito‐type cyclization was triggered. The 6‐endo‐dig Myers–Saito‐type cyclization gave access to benzo[b]fluorenes, while the Schmittel pathway (5‐exo‐dig) delivered benzofulvenes as final products. In special cases a yet unknown pathway was opened by the ambiphilic nature of the allene moiety. In these cases completely different products were obtained by the nucleophilic attack of the alkyne moiety onto the allene that can also act as an electrophile. Mechanistic studies revealed that diradical pathways can be ruled out for this type of tandem cyclization reactions and it is shown that both steps of the reaction cascade are catalyzed by the gold complex.     

Pd‐Catalyzed Cyclocarbonylation of 2‐(2‐Bromoaryl)indoles with CO as a C1 Source: Selective Access to 6 H‐Isoindolo[2,1‐a]indol‐6‐ones and Indeno[1,2‐b]indol‐10(5 H)‐ones

A highly efficient and regioselective synthetic route to 6 H‐isoindolo[2,1‐a]indol‐6‐ones and indeno[1,2‐b]indol‐10(5 H)‐ones through the Pd‐catalyzed cyclocarbonylation of 2‐(2‐bromoaryl)indoles under atmospheric CO pressure has been achieved. Notably, the regioselectivity of the reaction was exclusively dependent on the structural characteristics of the indole substrates. With N‐unsubstituted indoles as the starting materials, the reaction afforded 6H‐isoindolo[2,1‐a]indol‐6‐ones in good‐to‐excellent yields. On the other hand, with N‐substituted indoles as the substrates, the reaction gave indeno[1,2‐b]indol‐10(5 H)‐ones in a highly regioselective manner.     

Self‐Relay Gold(I)‐Catalyzed Pictet–Spengler/Cyclization Cascade Reaction for the Rapid Elaboration of Pentacyclic Indole Derivatives

Gold‐catalyzed cascade reactions allow the rapid elaboration of pentacyclic indolo[2,3‐a]quinolizidines from N‐allyl tryptamines and ortho‐alkynylarylaldehydes. The tandem process combines a gold‐catalyzed Pictet‐Spengler reaction and a cyclization occurring concomitantly with an allyl transfer from the nitrogen atom to the stilbene function. Various substituted allyls were successfully transferred, furnishing the products in yields typically ranging from 60–98 % in high diastereoselectivity. Tryptamines bearing a butenol chain undergo an additional cyclization to chiral hemiaminals in high diastereoselectivities.     

Ming‐Phos/Gold(I)‐Catalyzed Stereodivergent Synthesis of Highly Substituted Furo[3,4‐d][1,2]oxazines†

A gold(I)‐catalyzed asymmetric intermolecular tandem [3+3]‐cyclization reaction of 2‐(1‐alkynyl)‐2‐ alken‐1‐ones with nitrones has been developed by using Ming‐Phos as a chiral ligand. This method enables access to the stereodivergent synthesis of highly substituted furo[3,4‐d][1,2]oxazines in excellent efficiency and stereoselectivity (up to 99% yield, 99% ee, >20 : 1 dr).     

The Use of Pinner Type Reaction for the Synthesis of New Indeno[2,1‐c]pyridine‐4‐carbonitrile Derivatives

An efficient and convenient route was developed for the synthesis of new pyridinecarbonitrile derivatives by using the Pinner type of reaction. The 2‐((E)‐2‐((dimethylamino)methylene)‐1,2‐dihydro‐5,6‐dimethoxyinden‐3‐ylidene) malononitrile 2 was reacted in the presence of dry HCl gas to yield 3‐chloro‐6,7‐dimethoxy‐9H‐indeno[2,1‐c]pyridine‐4‐carbonitrile ( 3 ) in good yield. The S_NAr reaction on compound 3 with various nucleophiles yielded 3‐substituted pyridinecarbonitriles 4 , 5 , 6 , 7 , 8 , 9 in moderate to good yield.     

Superacid‐catalyzed Friedel–Crafts phosphination of 2‐hydroxybiphenyls with phosphorus trichloride

Cyclic phosphorus compounds, 6H‐dibenz[c,e][1,2]oxaphosphorin‐6‐oxide derivatives, were efficiently synthesized by the Friedel–Crafts reaction of 2‐hydroxybiphenyls with phosphorus trichloride in the presence of superacids, especially trifluoromethanesulfonic acid (TfOH) as a catalyst. TfOH was investigated for the first time as an effective catalyst for the aromatic phosphination of 2‐hydroxybiphenyls.     

Synthesis of New Functionalized Heterocyclic [4,3,3] Propellanes via Three‐component Reaction Based on Ninhydrin–Phenol Adducts

Three‐component reaction between ninhydrin–phenol adducts, dialkyl acetylenedicarboxylates, and triphenylphosphine was investigated. Utilizing this protocol, dialkyl 10‐oxo‐10H‐4b,9b‐(epoxyethanooxy)indeno[1,2‐b]benzofuran‐12,13‐dicarboxylates as functionalized heterocyclic [4,3,3] propellanes was synthesized in 6‐endo‐trig cyclization mode. 8‐hydroxyquinoline showed serendipitous reactivity and produced para substituted adduct in the reaction with ninhydrin in acetic acid media and hence produced dialkyl 8a‐(4‐(alkoxycarbonyl)‐2‐oxo‐2H‐pyrano[3,2‐h]quinolin‐6‐yl)‐8‐oxo‐8,8a‐dihydro‐2H‐indeno[2,1‐b]furan‐2,3‐dicarboxylate in the reaction with dialkyl acetylenedicarboxylates and PPh₃.     

A Mechanistic Study of the Utilization of arachno‐Diruthenaborane [(Cp*RuCO)2B2H6] as an Active Alkyne‐Cyclotrimerization Catalyst

The reaction of nido‐[1,2‐(Cp*RuH)₂B₃H₇] ( 1 a , Cp*=η⁵‐C₅Me₅) with [Mo(CO)₃(CH₃CN)₃] under mild conditions yields the new metallaborane arachno‐[(Cp*RuCO)₂B₂H₆] ( 2 ). Compound 2 catalyzes the cyclotrimerization of a variety of internal‐ and terminal alkynes to yield mixtures of 1,3,5‐ and 1,2,4‐substituted benzenes. The reactivities of nido‐ 1 a and arachno‐ 2 with alkynes demonstrates that a change in geometry from nido to arachno drives a change in the reaction from alkyne‐insertion to catalytic cyclotrimerization, respectively. Density functional calculations have been used to evaluate the reaction pathways of the cyclotrimerization of alkynes catalyzed by compound 2 . The reaction involves the formation of a ruthenacyclic intermediate and the subsequent alkyne‐insertion step is initiated by a [2+2] cycloaddition between this intermediate and an alkyne. The experimental and quantum‐chemical results also show that the stability of the metallacyclic intermediate is strongly dependent on the nature of the substituents that are present on the alkyne.