Chiral aziridine-2-carboxylates: versatile precursors for functionalized tetrahydroisoquinoline (THIQ) containing heterocycles

Preparation of functionalized 3,4-dihydroisoquinolines 17a–j from (S)-N-methoxy-N-methyl-1-[(R)-1-phenylethyl]aziridine-2-carboxamide 4 is an effective route for the synthesis of 3-(hydroxymethyl)-1,2,3,4-tetrahydroisoquinolin-4-ols. Stereoselective reduction of the cyclic imines 17a–j resulted in (1S,3S,4R)-4-(tert-butyldimethylsilyl-oxy)-3-[(tert-butyldimethylsilyloxy)methyl]-6,7-dimethoxy-1,2-disubstituted-1,2,3,4-tetrahydroisoquinolines and the desilylation of the TBS groups afforded (1S,3S,4R)-3-(hydroxymethyl)-6,7-dimethoxy-1,2-disubstituted-1,2,3,4-tetrahydroisoquinolin-4-ols 19a–i in good yields. Also, an asymmetric synthesis of novel tetracyclic 3-(hydroxymethyl)-1,2,3,4-tetrahydroisoquinolin-4-ols 23 and 25 was successfully achieved via Pd-catalyzed N-arylation and C–C coupling reaction.     

Synthesis of 6,7-dimethoxy-1-[(halophenoxy)-methyl]-1,2,3,4-tetrahydroisoquinolines

Some 6,7-dimethoxy-1-[(halophenoxy)methyl]-1,2,3,4-tetrahydroisoquinolines were synthesized from N-[2-(3,4-dimethoxyphenyl)ethyl]-2-chloroacetamide via three steps in good yield.     

Synthesis of 2,3,10,11 -tetraalkoxy-substituted tetrahydrobenzo [a] naphtho [1,2-g] quinolizines

2 Four3,10,11-tetraalkoxy-substituted 5,6,15,15a-tetrahydro-8H-benzo[a]naphtho[1,2-g]-quinolizines were prepared by the Pictet-Spengler cyclization of the respective 1-(6,7-dialkoxy-2-naphthylmethyl)-6,7-dialkoxy-1,2,3,4-tetrahydroisoquinolines. The latter compounds were obtained by a chemical reduction of the corresponding dihydro compounds, which, in turn, were formed by a Bischler-Napieralski cyclization of the appropriate amides.     

Saturated heterocycles. 57. Synthesis of 4-substituted-9,10-dialkoxy-1,6,7,11b-tetrahydro-2H-pyrimido[6,1-a]isoquinolin-2-ones

A large number of 4-substituted-9,10-dialkoxy-1,6,7,11b-tetrahydropyrimido[6,1-a]isoquinolin-2-ones were prepared by the reaction of 1-(ethoxycarbonylmethyl)-6,7-dialkoxy-1,2,3,4-tetrahydroisoquinolines with iminoethers. Reaction of the corresponding isoquinoline-1-acetic acid derivatives with iminoethers led to the formation of N-acyl-1,2,3,4-tetrahydroisoquinolin-1-acetamides. In the hydrolysis of the prepared 4-substituted-pyrimido[6,1-a]isoquinolin-2-ones, the corresponding N-acyl-1,2,3,4-tetrahydroisoquinolin-1-acetamides were obtained. While reduction of the 4-phenyl derivative resulted in the corresponding 1,3,4,6,7,11b-hexahydropyrimidinone. The steric structures of the tetrahydro- and hexahydropyrimido[6,1-a]isoquinolines were determined by nmr spectroscopy.     

PREPARATION OF 1,7-DISUBSTITUTED-1,2,3,4-TETRAHYDROISOQUINOLINES

ABSTRACT

A simple procedure for the preparation of 1,7-disubstituted-1,2,3,4-tetrahydroisoquinolines from 3,4-dihydroisoquinoline (2) is presented. This strategy overcomes the limitation of cyclisation approaches which generally require electron rich ring systems. A variety of 1-substituents has been incorporated using the appropriate organometallic or activated methylene nucleophile to prepare both electron rich (7a–f) and electron deficient 1,7-disubstituted-1,2,3,4-tetrahydroisoquinolines (16, 17).     

4,5-Dibenzyloxybenzyne as a synthon for diels-alder reactions. The synthesis of 6,7-dihydroxy-1,4-ethano-1,2,3,4-tetrahydroisoquinolines as rigid analogs of adrenergic agents. Assignment of proton and carbon-13 NMR parameters using homonuclear and heteronuclear two-dimensional chemical shift correlation NMR spectroscopy

The synthesis of several rigid analogs of catecholamine type of adrenergic agents is reported. Their synthesis began with a Diels-Alder cycloaddition of 4,5-dibenzyloxybenzyne (generated from 4,5-dibenzyloxyan-thranilic acid) to 1-(2-trans-phenylvinyl)-2-pyridone and 1-benzyl-3-benzyloxy-2-pyridone. The unsaturated amides so produced were reduced first with hydrogen and palladium and then with lithium aluminum hydride to provide 6,7-dihydroxy-1,4-ethano-1,2,3,4-tetrahydroisoquinolines. Homonuclear and heteronuclear two-dimensional chemical shift correlation nmr spectroscopy confirmed the structure of the bridged tetra-hydroisoquinolines and led to the unambiguous assignment of the ¹H and ¹³C nmr chemical shifts of key compounds.     

Microwave-assisted, solvent-free synthesis of 1-(α- or β-hydroxynaphthyl)-1,2,3,4-tetrahydroisoquinolines by the Mannich reaction

As a new extension of the Mannich reaction of naphthols, 1-(hydroxynaphthyl)-substituted 1,2,3,4-tetrahydroisoquinolines were synthesized by the nucleophilic addition of 1- or 2-naphthol to 3,4-dihydroisoquinolines under solvent-free conditions, using microwave irradiation. The additions to 3-methyl-6,7-dimethoxy-3,4-dihydroisoquinoline proved to be a highly diastereoselective processes, resulting in the cis isomers as the main or the only products.     

Studies on Debenzylation and Photolysis of 1-Benzyl- and 1-(β-Phenethyl)-1,2,3,4-tetrahydroisoquinolines

Debenzylation of 1-(3-benzyloxybenzyl)-1,2,3,4-tetrahydroisoquinolines 1 , 6 , 7 with hydrochloric acid and ethanol gave the corresponding phenolic isoquinolines 2 , 8 , 9 and tetrahydroprotoberberines 4 , 12 , 13 . Compounds 2 , 8 , 9 on photolysis also gave, besides the expected noraporphines 3 , 10 , 11 , the tetrahydroprotoberberines 4 , 12 , 13 [1–4] (Schemes 1 and 2). 6-Benzyloxy-1-(5-benzyloxy-2-bromo-benzyl)-1,2,3,4-tetrahydroisoquinoline (27a) containing no methoxy or methylenedioxy groups either in ring A or C does not give protoberberine during debenzylation; but 28 , the debenzylation product of 27a , on photolysis gives both the noraporphine 29 and the tetrahydroprotoberberine 30 (Scheme 6), proving that during debenzylation of 1-(3-benzyloxybenzyl)-1,2,3,4-tetrahydroisoquinolines containing additional methoxy or methylenedioxy groups, the necessary formaldehyde comes from the latter groups. During photolysis both the methoxy groups (methylenedioxy groups) and the C(3) atom of the tetrahydroisoquinoline moiety provide the formaldehyde. Veratrole under debenzylation and photolytic conditions and tetrahydroisoquinoline under the latter condition also give rise to formaldehyde (Schemes 8 and 10). The novel bromohomoprotoberberine 43 along with 42 was formed during debenzylation of the 1-phenethyl-1,2,3,4-tetrahydroisoquinoline 41 . Photolysis of 42 yielded the novel nor-homoaporphine 44 , in addition to 43 ; the latter was debrominated to give the homoberbine 45 .     

Synthesis of 6,7-dimethoxy-1-halobenzyl-1,2,3,4-tetrahydroisoquinolines

Some 6,7-dimethoxy-1-halobenzyl-1,2,3,4-tetrahydroisoquinolines were synthesized from 2-(3,4-dimethoxyphenyl)ethylamine and halophenylacetic acids in three steps in good yield.     

Synthesis of 11-aza-5H-benzophenoxazin-5-one and 11-Aza-5H-pyridophenoxazin-5-one derivatives

The 1,6-disubstituted- and 4,6-disubstituted-11-aza-5H-benzo[a]phenoxazin-5-one as well as 6-substituted-11-aza-5H-pyrido[a]phenoxazin-5-one derivatives were prepared by the condensation of 2-amino-3-hydroxypyridine with 5-substituted-2,3-dihalogeno-1,4-naphthoquinones and 6,7-dibromo-5,8-quinolinequinone respectively. The resulting compounds were subjected to reduction, acetylation, dehalogenation and reaction with aniline.     

A Concise Synthesis of 2‐Amino‐1,2,3,4‐tetrahydronaphthalene‐6,7‐diol (‘6,7‐ADTN’) from Naphthalene‐2,3‐diol

2‐Amino‐1,2,3,4‐tetrahydronaphthalene‐6,7‐diol ( 2 ; 6,7‐ADTN) was synthesized starting from naphthalene‐2,3‐diol in seven steps and with an overall yield of 44%. Methylation of naphthalene‐2,3‐diol with dimethyl sulfate, followed by Friedel? Crafts acylation with AcCl, gave 2‐acetyl‐6,7‐dimethoxynaphthalene. 2‐Acetyl‐6,7‐dimethoxynaphthalene was converted to 6,7‐dimethoxynaphthalene‐2‐carboxylic acid by a haloform reaction. Birch reduction of the carboxylic acid with 4 mol‐equiv. of Na in liquid ammonia afforded 1,2,3,4‐tetrahydro‐6,7‐dimethoxynaphthalene‐2‐carboxylic acid, from which 2 was obtained by a Curtius reaction, followed by hydrogenolysis and demethylation.     

A New Convenient Approach to Preparation of 5 or 6 or 7-Nitro-1,2,3,4-Tetrahydrisoquinolines and 2-Alkylsulfonyl-5 or 6 or 7-Nitro-1,2,3,4-Tetrahydroisoquinolines

N-alkylsulfonyl-p or m or o -nitrophenylethylamines were treated with (HCHO)n in 60% H₂SO₄/HOAc to give N-alkylsulfonyl-5 or 6 or 7-nitro-1,2,3,4-tetrahydroisoquinolines, then hydrolyzed with 40% HBr to give 5 or 6 or 7-nitro-1,2,3,4-tetrahydroisoquinolines     

Alkylation of N-boc-1,2,3,4-tetrahydroisoquinolines in the 1-position and its application to the synthesis of isoquinoline alkaloids

Boc-protected 1,2,3,4-tetrahydroisoquinolines 2 can be lithiated with t-butyllithium in the presence of N,N,N',N',-tetramethylethylenediamine. Reaction of the anion with alkyl halides provides 1-alkyl N-Boc-1,2,3,4-tetrahydroisoquinolines in 67–71% yield. The protecting group is easily removed in high yield with trifluoroacetic acid. The alkaloids salsolidine ( 8 ) and laudanosine ( 11 ) were synthesized in racemic form using this method.     

Synthesis of 7H-tetrazolo[1,5-c]pyrrolo[3,2-e]pyrimidines and their reductive ring cleavage to 4-aminopyrrolo[2,3-d]pyrimidines

Some new 7,9-disubstituted 7H-1,2,3,4-tetrazolo[1,5-c]pyrrolo[3,2-e]pyrimidines 5 have been synthesized either by diazotization of 4-hydrazino-5,7-disubstituted-7H-pyrrolo[2,3-d]pyrimidines 4 obtained by hydrazinolysis of 4-chloro-5,7-disubstituted-7H-pyrrolo[2,3-d]pyrimidines 3 or via a substitution reaction between 3 and sodium azide. 5,7-Disubstituted-7H-pyrrolo[2,3-d]pyrimidin-4(3H)-ones 2 were obtained by cyclocondensation of 2-amino-3-cyano-1,4-disubstituted pyrroles 1 with formic acid which on chlorination using phosphorus oxychloride afforded 3 . A novel route for the synthesis of 4-amino-5,7-disubstituted-7H-pyrrolo[2,3-d]pyrimidines 6 by the reductive ring cleavage of 5 has been reported.     

The synthesis of 1,4-ethano-1,2,3,4-tetrahydroisoquinolines as rigid analogues of adrenergic agents

The Diels-Alder addition of benzyne and 4,5-dimethoxybenzyne to 1-(2-trans-phenylvinyl)-2-pyridone and 1-benzyl-3-benzyloxy-2-pyridones provided members of the 1,4-etheno-3-oxo-1,2,3,4-tetrahydroisoquinoline system. Catalytic reduction of these adducts yielded the corresponding tricyclic lactams. Lithium aluminum hydride reduction of these lactams produced a number of 1,4-ethano-1,2,3,4-tetrahydroisoquinolines.     

A Convenient Synthesis of 3-Aryl-2-Methyl-3,4-Dihydro-1(2H)-Isoquinolones and -1,2,3,4-Tetrahydroisoquinolines

A new methodology for the synthesis of 3-aryl-2-methyl-3,4-dihydro-2H-isoquinolin-l-ones and 3-aryl-2-methyl-1,2,3,4-tetrahydroisoquinolines is reported.     

Synthese einiger 8-substituierter 2-Methyl-1,2,3,4-tetrahydroisochinoline

Synthesis of Some 8-Substituted 2-Methyl-1,2,3,4-tetrahydroisoquinolines A general route to 8-substituted tetrahydroisoquinolines is exemplified by the preparation of the 2-methyl-1,2,3,4-tetrahydroisoquinolin-8-ol ( 11 ), the -8-carbaldehyde oxime ( 12 ) and the -8-carbonitrile ( 13 ). It involves the conversion of isoquinoline ( 1 ) by partially modified Steps 1, 2, 3, and 5 (see the Scheme) into the 5-bromo-8-nitro derivative 5 , reduction of the latter to the 8-amino derivative 8 and replacement of the NH₂-group with an appropriate substituent by a Sandmeyer-like reaction. The selective reductions of the N-containing ring in 6 (Steps 5, 6, and 8) and of the NO₂-group in 5 (Steps 4 and 7) were also studied.     

Synthesis of stable azomethine ylides by the rearrangement of 1,3-dipolar cycloadducts of 3,4-dihydroisoquinoline-2-oxides with DMAD

1-Aryl-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolines were prepared according to a one-pot procedure involving the reaction of 2-(3,4-dimethoxyphenyl)-ethylamine with aromatic aldehydes in TFA at reflux. The tetrahydroisoquinolines were treated with H₂O₂-WO₄²⁻ in methanol at room temperature to give the corresponding 3,4-dihydroisoquinoline-2-oxides. Treatment of these cyclic nitrones with DMAD in toluene at room temperature gave the corresponding isoxazolo[3,2-a]isoquinolines. These compounds were heated in toluene at reflux to give the corresponding ylides in high yields (Method A). The effect of the substituents on the rate of the rearrangement of such compounds prompted us to discuss a new mechanism involving consecutive C-C bond heterolysis and 1,3-sigmatropic shift. A one-pot reaction involving the treatment of the nitrones with equimolar amounts of DMAD in refluxing toluene also gave the ylides (Method B). The structures of the prepared compounds were elucidated by spectral means and elemental analyses.     

Tungstophosphoric acid catalyzed synthesis of N-sulfonyl-1,2,3,4-tetrahydroisoquinoline analogs

An operationally simple and eco-friendly protocol has been developed for the synthesis of N-sulfonyl-1,2,3,4-tetrahydroisoquinolines 3 using the modified Pictet-Spengler reaction of N-sulfonylphenylethylamines 1 and various aldehydes 2 in the presence of tungstophosphoric acid hydrate.     

Synthesis and structure-active relationship of 1-aryl-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline anticonvulsants

We have previously disclosed that some 6,7-dimethoxyisoquinoline derivatives are able to produce anticonvulsant effects in different animal models of epilepsy. Following these studies this paper describes the synthesis of a small series of new 1-aryl-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolines strictly related to previously reported analogues. This novel series of isoquinolines was designed on the basis of well defined structure-active relationship (SAR) information already acquired for this class of anticonvulsant agents. The pharmacological effects of the new synthesized compounds were evaluated against audiogenic seizures in Dilute Brown non-Agouti (DBA/2) mice. The preliminary pharmacological screening led to the identification of a new active molecule the 2-acetyl-1-(4'-methylphenyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline (6d) that displayed significant anticonvulsant activity. Computational studies helped to rationalize these obtained pharmacological results.