Application of copper(i) iodide/diorganoyl dichalcogenides to the synthesis of 4-organochalcogen isoquinolines by regioselective cn and cchalcogen bond formation

A copper-catalyzed cyclization of (ortho-alkynyl)benzaldimines with diorganoyl dichalcogenides allowed the synthesis of 4-organochalcogen isoquinolines, whereas the presence of base in the reaction medium inhibited the product formation producing the undesirable isoquinoline without the organochalcogen atom at the 4-position. The cyclization reaction was carried out by using CuI (20?%) as a catalyst with diorganoyl dichalcogenides (1.5?equiv) in the presence of DMF at 100?°C. Furthermore, the reaction did not require an argon atmosphere and was carried out in an open flask. The cyclization reaction tolerated a variety of functional groups both in ortho-alkynylbenzaldimines and diorganoyl dichalcogenides, such as trifluoromethyl, chloro, fluorine, and methoxyl, to give the six-membered heterocyclic ring exclusively through a 6-endo-dig cyclization process. The organochalcogen group present at the 4-position of the isoquinoline ring was further subjected to a selective chalcogen-lithium exchange reaction followed by the addition of aldehydes to afford the desired secondary alcohols in good yields. The obtained isoquinolines also proved to be suitable substrates for the Suzuki and Sonogashira coupling conditions affording the corresponding products through C?C bond formation.     

Aryl radical cyclizations of 1-(2'-bromobenzyl)isoquinolines with AIBN-Bu3SnH: formation of aporphines and indolo

[reaction: see text] Radical cyclization of alkoxy-substituted 1-(2'-bromobenzyl)-3,4-dihydroisoquinolines 1 with AIBN-Bu3SnH gave 6a,7-dehydroaporphines 2 preferentially. A steric repulsion between the respective alkoxy groups at the 7- and 3'-positions gave 5,6-dihydroindolo[2,1-a]isoquinolines 3 in a "disfavored" 5-endo cyclization mode. Radical cyclizations of the related substrates, such as 1-(2'-bromobenzoyl)isoquinolines or 1-(2'-bromo-alpha-hydroxybenzyl)isoquinolines, were also found to give the corresponding oxoaporphines or oxyaporphines.     

Application of Copper(I) Iodide/Diorganoyl Dichalcogenides to the Synthesis of 4‐Organochalcogen Isoquinolines by Regioselective C?N and C?Chalcogen Bond Formation

A copper‐catalyzed cyclization of (ortho‐alkynyl)benzaldimines with diorganoyl dichalcogenides allowed the synthesis of 4‐organochalcogen isoquinolines, whereas the presence of base in the reaction medium inhibited the product formation producing the undesirable isoquinoline without the organochalcogen atom at the 4‐position. The cyclization reaction was carried out by using CuI (20 %) as a catalyst with diorganoyl dichalcogenides (1.5 equiv) in the presence of DMF at 100 °C. Furthermore, the reaction did not require an argon atmosphere and was carried out in an open flask. The cyclization reaction tolerated a variety of functional groups both in ortho‐alkynylbenzaldimines and diorganoyl dichalcogenides, such as trifluoromethyl, chloro, fluorine, and methoxyl, to give the six‐membered heterocyclic ring exclusively through a 6‐endo‐dig cyclization process. The organochalcogen group present at the 4‐position of the isoquinoline ring was further subjected to a selective chalcogen–lithium exchange reaction followed by the addition of aldehydes to afford the desired secondary alcohols in good yields. The obtained isoquinolines also proved to be suitable substrates for the Suzuki and Sonogashira coupling conditions affording the corresponding products through C? C bond formation.     

Synthesis of 1-hydroxy-substituted pyrazolo[3,4-c]- and pyrazolo[4, 3-c]quinolines and -isoquinolines from 4- and 5-aryl-substituted 1-benzyloxypyrazoles

1-Hydroxypyrazolo[3,4-c]quinoline (22), 1-hydroxypyrazolo[4, 3-c]quinoline (21), 1-hydroxypyrazolo[3,4-c]isoquinoline (20), and 1-hydroxypyrazolo[4,3-c]isoquinoline (19) were prepared from 1-benzyloxypyrazole (6), establishing the pyridine B-ring in the terminal step. The pyridine ring of pyrazoloquinolines 14 and 18 was formed via cyclization of a formyl group at C-4 or C-5 and an amino group of a 2-aminophenyl substituent at C-5 or C-4 in 1-benzyloxypyrazole. The pyridine ring of pyrazoloisoquinolines 5 and 9 was created via cyclization of a formyl group in a 2-formylphenyl substituent at C-4 or C-5 with an iminophosphorane group installed at C-5 or C-4 of 1-benzyloxypyrazole by lithiation followed by reaction with tosyl azide and then with tributylphoshine utilizing the Staudinger/aza-Wittig protocol. The 2-aminophenyl and the 2-formylphenyl substituent were introduced at C-5 or C-4 by regioselective metalation followed by transmetalation to the pyrazolylzinc halide and subsequent palladium-catalyzed cross-coupling with 2-iodoaniline or 2-bromobenzaldehyde. The order of reactions and use of protecting groups in the individual sequences have been optimized. The 1-benzyloxy-substituted pyrazoloquinolines and isoquinolines thus obtained were debenzylated by strong acid to the corresponding 1-hydroxy-substituted pyrazoloquinolines and isoquinolines 19-22.     

Synthesis of 3-substituted 4-aroylisoquinolines via Pd-catalyzed carbonylative cyclization of 2-(1-alkynyl)benzaldimines

A number of 3-substituted 4-aroylisoquinolines have been prepared in good yields by treating N-tert-butyl-2-(1-alkynyl)benzaldimines with aryl halides in the presence of CO and a palladium catalyst. Synthetically the methodology provides a simple and convenient route to isoquinolines containing an aryl, alkyl, or vinylic group at C-3 and an aroyl group at C-4 of the isoquinoline ring. The reaction is believed to proceed via cyclization of the alkyne containing a proximate nucleophilic center promoted by an acylpalladium complex.     

Synthesis of H-pyrazolo[5,1-a]isoquinolines via copper(II)-catalyzed oxidation of an aliphatic C-H bond of tertiary amine in air

A multicomponent reaction of 2-alkynylbenzaldehyde, sulfonohydrazide, and tertiary amine is discovered, which generates the unexpected H-pyrazolo[5,1-a]isoquinolines in good yields under mild conditions. In the reaction process, silver(I)-catalyzed intramolecular cyclization and copper(II)-catalyzed oxidation of an aliphatic C-H bond of tertiary amine in air are involved.     

Coinage metals-catalyzed cascade reactions of aryl alkynylaziridines: silver(I)-single vs gold(I)-double cyclizations

Alkynylaziridines carrying an aryl group could be efficiently converted into aminoallenylidene isochromans, isoquinolines, or tetrahydronaphtalenes with silver(I) salts and into 1-azaspiro[4.5]decane derivatives with gold(I) complexes. Mechanistic investigations revealed that both Ag- and Au-catalyzed reactions involved a Friedel-Crafts type intramolecular reaction leading to an allene and that Au also rapidly promoted a second intramolecular cyclization of the aminoallene intermediate to the corresponding spiro derivative. Stereochemical investigations suggested an anti-SN(2)'-type pathway for the first cyclization leading to a stereodefined allene, which could then be cyclized to the corresponding stereodefined spiro product. These results highlight the duality between oxo- or azaphilicity and alkynophilicity of Ag and Au as well as their complementarity in terms of reactivity.     

New approaches to the synthesis of benzo[h]pyrroloisoquinoline derivatives

An effective strategy for the synthesis of benzo[h]pyrrolo[2,1-a]isoquinoline derivatives has been developed. The process can be described as a one-pot domino reaction that consists of an initial Michael addition, intramolecular cyclization, and subsequent transformations leading to the formation of the desired products. A wide range of structurally diverse hydrogenated benzo[h]pyrrolo[2,1-a]isoquinolines were obtained in 34–98% yield. This strategy represents an efficient catalyst-free procedure that allows the synthesis of previously inaccessible compounds.     

Rhodium(III)-catalyzed cyclization-olefination of N-acetoxyl ketoimine-alkynes

N-Acetoxyl ketoimine-alkynes undergo Rh(III)-catalyzed oxidative olefination to afford (2-acetoxymethyl)isoquinolines bearing an ortho-olefinated aryl group via a sequence that involves (1) Rh(III)-catalyzed alkyne cyclization with intramolecular 1,3-acetoxyl migration and (2) isoquinoline-directed ortho C-H olefination.     

A simplified isoquinoline synthesis

A simple variation of the Pomeranz-Fritsch cyclization provides a short, efficient route to isoquinolines. Treatment of benzylic halides or mesylates 1 with the sodium anion of N-tosyl aminoacetaldehyde dimethyl acetal (2) followed by acid-catalyzed cyclization provides an effective, two-step preparation of isoquinolines 4.     

Reaction of 1-alkylthioisoquinolinium salts with active methylene compounds

2-Alkyl-1-alkylthioisoquinolinium salts were readily prepared from 2-alkyl-1(2H)-isoquinolones via 2-alkyl1(2H)-thioisoquinolones in two steps. Under mild conditions, the reaction of 2-alkyl-1-alkylthioisoquinolinium salts with active methylene compounds in the presence of sodium hydride afforded 2-alkyl-1-(substituted methylene)iso-quinolines in good yields. Pyrrolo[2,1-a]isoquinolines were synthesized by the cyclization of 2-benzyl-1-(substituted methylene)isoquinolines using acetic anhydride.     

New strategy for the synthesis of tetrahydroisoquinoline alkaloids

[reaction: see text] A general strategy for the formation of 1,3-cis-substituted tetrahydroisoquinolines is described from ortho-iodo imines involving Larock isoquinoline synthesis, addition of organolithium compounds to unactivated isoquinolines, and ionic hydrogenation. In addition, a new synthesis of lactams via an unprecedented azide cyclization in the presence of a sulfonium ion is described.     

A versatile synthesis of pyrazolo[3,4-c]isoquinoline derivatives by reaction of 4-aryl-5-aminopyrazoles with aryl/heteroaryl aldehydes: the effect of the heterocycle on the reaction pathways

The reaction of 4-(3,4-dimethoxyphenyl)-5-aminopyrazoles 7A-D with aromatic and heterocyclic aldehydes in strong acidic media (trifluoroacetic or formic acid) has been studied. The initial azomethine derivatives 8 undergo cyclization similar to the Pictet-Spengler condensation to form the intermediate 4,5-dihydroisoquinolines 9 which readily dehydrogenate giving 5-aryl(heteroaryl)-pyrazolo[3,4-c]isoquinoline derivatives 10 as the final products. Whereas for benzaldehyde and its derivatives this one-pot synthesis presents a convenient general route to 5-aryl-pyrazolo[3,4-c]isoquinolines 10, in the case of heterocyclic aldehydes the product structure varies markedly with the structure of the aldehyde used: (i) 3-pyridyl-, 3-quinolyl-, 3-thienyl-, and 1,2,3-thiadiazolyl-5-carboxaldehydes give 5-heteroarylpyrazolo[3,4-c]isoquinolines; (ii) 1-methylbenzimidazolyl-2-carboxaldehyde gives only intermediate azomethine 8Dh, which does not cyclize; (iii) 1-R-3-indolylcarboxaldehydes (R = H, CH3, CH2Ph) eliminate the heteroaryl fragment resulting in 5-unsubstituted pyrazolo[3,4-c]isoquinolines 11. Thienyl-2-carboxaldehyde reacts by both pathways (i) and (iii) depending on the reaction conditions. The single crystal X-ray structures for 10Dj, 10Cd and 11D provide confirmation of the different types of products formed in these reactions. Mechanisms which explain these transformations are presented.     

An efficient route to diverse H-pyrazolo[5,1-a]isoquinolines via sequential multi-component/cross-coupling reactions

Multi-component reaction of 2-alkynylbenzaldehyde, sulfonohydrazide, electrophile (bromine or iodine), and ketone or aldehyde under mild conditions proceeds smoothly to afford the functionalized H-pyrazolo[5,1-a]isoquinolines in good yields. This one-pot process involves intermolecular condensation, electrophilic cyclization, nucleophilic addition, intramolecular condensation, and aromatization. The resulting halo-containing H-pyrazolo[5,1-a]isoquinolines could be further elaborated via palladium-catalyzed cross-coupling reactions.     

Reductive cyclization of 1-(2-nitroaryl)isoquinoline derivatives

Isoquinoline derivatives 3b and 3c were prepared and their triethyl phosphite mediated reductive cyclization reactions investigated. Only the indazolo[3,2-a]isoquinolines 4b and 4c were formed.     

Synthesis of isoquinolines and pyridines by the palladium/copper-catalyzed coupling and cyclization of terminal acetylenes and unsaturated imines: the total synthesis of decumbenine B.

Monosubstituted isoquinolines and pyridines have been prepared in good to excellent yields via coupling of terminal acetylenes with the tert-butylimines of o-iodobenzaldehydes and 3-halo-2-alkenals in the presence of a palladium catalyst and subsequent copper-catalyzed cyclization of the intermediate iminoalkynes. In addition, isoquinoline heterocycles have been prepared in excellent yields via copper-catalyzed cyclization of iminoalkynes. The choice of cyclization conditions is dependent upon the nature of the terminal acetylene that is employed, as only aryl and alkenyl acetylenes cyclize under the palladium-catalyzed reaction conditions that have been developed. However, aryl-, vinylic-, and alkyl-substituted acetylenes undergo palladium-catalyzed coupling and subsequent copper-catalyzed cyclization in excellent yields. The total synthesis of the isoquinoline natural product decumbenine B has been accomplished in seven steps and 20% overall yield by employing this palladium-catalyzed coupling and cyclization methodology.     

Silver triflate and palladium acetate co-catalyzed reaction of N'-(2-alkynylbenzylidene)hydrazide with N-allyl ynamide

A silver triflate and palladium acetate co-catalyzed reaction of N'-(2-alkynylbenzylidene)hydrazide with N-allyl ynamide is described, which generates 2-amino-H-pyrazolo[5,1-a]isoquinolines in good to excellent yield. The transformation proceeds with high efficiency through 6-endo cyclization, [3 + 2] cycloaddition, 3,3-sigmatropic rearrangement, and aromatization.     

A Facile method to transform trans-4-carboxy-3,4-dihydro-3-phenyl- 1(2H)-isoquinolones to indeno[1,2-c]isoquinolines

The indeno[1,2-c]isoquinolines are an important class of topoisomerase I inhibitors with anticancer activity. The condensation of Schiff bases with homophthalic anhydrides provides a mixture of cis- and trans-4-carboxy-3,4-dihydro-3-phenyl-1(2H)isoquinolones. Although the cis products can be readily converted to indeno[1,2-c]isoquinolines with thionyl chloride, the trans products do not afford indeno[1,2-c]isoquinolines using this method. The present report describes a route for conversion of the trans diastereomers to indeno[1,2-c]isoquinolines using selenoxide elimination and Friedel-Crafts cyclization chemistry.     

Synthesis of 4-(1-alkenyl)isoquinolines by palladium(II)-catalyzed cyclization/olefination

A variety of 4-(1-alkenyl)-3-arylisoquinolines have been prepared in moderate to excellent yields by the Pd(II)-catalyzed cyclization of 2-(1-alkynyl)arylaldimines in the presence of various alkenes. The introduction of an o-methoxy group on the arylaldimine promotes the Pd-catalyzed cyclization and stabilizes the resulting Pd(II) intermediate, improving the yields of the isoquinoline products. Ketone-containing isoquinolines 36 and 49-51 have also been prepared by this process when unsaturated alcohols are employed as the alkenes.     

Palladium and copper cocatalyzed tandem N-H/C-H Bond functionalization: synthesis of CF3-containing indolo- and pyrrolo[2,1-a]isoquinolines

A palladium- and copper-catalyzed tandem N-H/C-H bond functionalization reaction of ortho-(2-chlorovinyl)bromobenzenes with indoles and pyrroles has been developed. A variety of CF(3)-containing indolo- and pyrrolo[2,1-a]isoquinolines were prepared in moderate to good yields via the cyclization of 1-bromo-2-(2-chloro-3,3,3-trifluoroprop-1-enyl)benzenes with indoles and pyrroles.