A contribution to the asymmetric synthesis of isoquinolines: Concise stereoselective approach to (3S,4S)-6,7-dimethoxy-4-hydroxy-3-phenyl-1,2,3,4-tetrahydroisoquinoline

A highly efficient stereoselective synthesis of (3S,4S)-6,7-dimethoxy-4-hydroxy-3-phenyl-1,2,3,4-tetrahydroisoquinoline 8 (e.e.=96%) starting from enantiomerically pure imine 3 is reported.     

R 和 s-1-(3'-溴-4'-甲氧基)苄基-2-甲基-6-甲氧基-7-羟基-1, 2,3,4-四氢异喹啉的合成

本文报道了R和S-1-(3'-溴-4'-甲氧基)苄基-2-甲基-6-甲氧基-7-羟基-1,2,3,4-四氢异喹啉的合成。     

Efficient enantioselective synthesis of (R)-2-acetyl-2-hydroxy-5,8-dimethoxy-1,2,3,4-tetrahydronaphthalene,the key intermediate in the synthesis of anthracycline antibiotics

A simple, efficient, enantioselective synthesis of (R)-2-acetyl-2-hydroxy-5,8-dimethoxy-1,2,3,4-tetrahydronaphthalene, the key intermediate in the synthesis of anthracycline antibiotics, is described. The synthetic procedure starts with the Sharpless asymmetric dihydroxylation of 2-acetyl-5,8-dimethoxy-3,4-dihydronaphthalene: the diol obtained is regioselectively transformed into the corresponding chloroacetate which is dehalogenated and saponified to give the desired title compound in four steps with satisfactory yield (52%). No separation step is necessary at any point of the synthetic process. An efficient procedure for the synthesis of the starting enone and the stereoselectivity of the methanolysis of the intermediate chloroacetate are also reported.     

Electrochemical oxidative substitution and dimerisation of 1-arylazo-2-naphthols,leading to a new synthesis of some unsymmetrical diarylamines

Some electron-rich 1-arylazo-2-naphthols undergo novel electrochemical oxidations, leading either to substitution by a nucleophilic aniline or to oxidative dimerisation. In the former case subsequent reduction of the azo bond provides a new route to unsymmetrical diarylamines.     

Oxazoline as a useful tool in organic synthesis: preparation of 4-aryl-1,2,3,4-tetrahydroisoquinoline alkaloid skeleton

New direct strategy for the synthesis of 4-aryl-1,2,3,4-tetrahydroisoquinolines. The key steps are based on oxazoline chemistry: nucleophilic substitution in an ortho-methoxyphenyloxazoline with a Grignard reagent and a 1,6-conjugate addition of a lithium amide to o-styrylphenyloxazoline.     

Expeditious One-Pot,Four-Step Preparation of 2-t-Butoxycarbonyl-6-hydroxy-1,2,3,4-tetrahydroisoquinoline and an Improved Conversion to Its 6-Cyano Derivative

3-Methoxy-phenethylamine was subjected to a sequential imination/Pictet–Spengler/demethylation/Boc protection sequence that allowed a one-pot preparation of N-Boc-6-hydroxy-1,2,3,4-tetrahydroisoquinoline 1. This intermediate was elaborated almost quantitatively via an improved triflation/cyanation procedure to its 6-cyano analog 2.     

Synthesis and oxidative aromatization of 5-acetyl-2-cyanoimino-6-methyl-4-phenyl-1,2,3,4-tetrahydropyrimidine with manganese dioxide

The synthesis of 5-acetyl-2-cyanoimino-6-methyl-4-phenyl-1,2,3,4-tetrahydropyrimidine has been carried out by reaction of N-[(tosyl)(phenyl)methyl]-N′-cyanoguanidine with acetylacetone in the presence of sodium hydride with subsequent acid catalyzed dehydration of the 4-hydroxy-2-imino-hexahydropyrimidine obtained. The oxidative aromatization of the tetrahydropyrimidine synthesized using manganese dioxide has been studied. It was found that the products formed depend on the reaction temperature and are either 5-acetyl-2-carbamoylamino-4-methyl-6-phenylpyrimidine or 5-acetyl-2-amino-4-methyl-6-phenylpyrimidine or a mixture of both.     

Isomerization-cyclization approach to the synthesis of 2-hydroxy-5-alkylidene-cyclopent-2-enones

[reaction: see text]. Propargyl vinyl ketones that are derived from the addition of 1-lithio-1-methoxymethoxy-2-ynes to morpholino enamides undergo isomerization followed by cyclization to alpha-methylene cyclopentenones upon exposure to silica gel.     

Various approaches to the use of 3-acetyl-2-amino-4-hydroxy-1,3-pentadienecarbonitrile in heterocyclic synthesis

Two approaches to the use of 3-acetyl-2-amino-4-hydroxy-1,3-pentadienecarbonitrile (1) in heterocyclic synthesis are considered. A method for preparing 3-acetyl-4-amino-5-cyano-2-methylpyridine directly from1 andN,N-dimethylformamide dimethylacetal (DMF DMA) was proposed, together with a synthetic route to 2-(2-amino-3-cyano-6-hydroxy-phenyl)-8-cyano-5-hydroxy-4-methylquinoline based on the transformation of hydroxyvinyl ketone1 into its diphenylboron chelate and condensation of the latter with DMF DMA. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 127–130, January, 1997.     

N-aryl-2-hydroxy-1,2,3,4-tetrahydropyridines and N-aryl-2-chloromethylene-1,2,3,4-tetrahydropyridines — successive intermediates in the Hantzsch synthesis of 1,4-dihydropyridines

Esters of 4-chloro-2-arylideneacetoacetic acid I and esters of N-arylaminocrotonic acid II form stable N-aryl-3,4-trans-2-hydroxy-1,2,3,4-tetrahydropyridines III. Their regio- and stereoselective dehydration results in N-aryl-2-chloromethylene-1,2,3,4-tetrahydropyridines with an exocyclic bond, IV. Compounds IV isomerize to the corresponding N-aryl-2-chloromethyl-1,4-dihydropyridines V in acid medium. Michael addition of compounds I and II in chloroform or benzene forms carbocyclic derivatives of cyclohexene VI.Latvian Institute of Organic Synthesis, Riga LV-1006. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 915–920, July, 1997.     

Total syntheses of conformationally constrained didemnin B analogues. replacements of N,O-dimethyltyrosine with L-1,2,3,4-tetrahydroisoquinoline and L-1,2,3,4-tetrahydro-7-methoxyisoquinoline.

The design and synthesis of two conformationally constrained analogues of didemnin B are described. The [N,O-Me(2)Tyr(5)]residue of didemnin B was replaced with L-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (Tic) and L-1,2,3,4-tetrahydro-7-methoxyisoquinoline-3-carboxylic acid (MeO-Tic), which mimic the N,O-dimethylated tyrosine while constraining the conformation of the molecule. Preliminary results indicate that the conformation of the [N,O-Me(2)Tyr(5)]residue closely matches the conformation imposed by the Tic replacement.     

A new method for the synthesis of 2-hydroxy-3-nitro-1,4-naphthoquinones: application to regiospecific preparation of unsymmetrical nitrobiquinones

Novel 2-hydroxy-3-nitro-1,4-naphthoquinones were synthesized by an improved method utilizing nitronium tetrafluoroborate in high yields. A subsequent conversion to 2-chloro-3-nitro-1,4-naphthoquinones and a substitution of the chlorine by hydroxyquinone anions yielded 3-nitro-2,2'-binaphthoquinones with a complete regiocontrol.     

The synthesis and transformation of ethyl 2-(2-acetyl-2-benzoyl-1-ethenyl)amino-3-dimethylaminopropenoate. A new synthesis of 2,3,4-trisubstituted pyrroles

The synthesis of ethyl 2-(2-acetyl-2-benzoyl-1-ethenyl)amino-3-dimethylarninopropenoate ( 4 ) from benzoylacetone ( 1 ) via 3-dimethylarninomethylenebenzoylacetone ( 2 ) and ethyl N-(2-acetyl-2-benzoyl-1-ethenyl)glycinate ( 3 ) and its transformation into 4-benzoyl-2-ethoxycarbonyl-3-methylpyrrole ( 9 ) is described. Cyclization of 4 into 9 represents a new synthesis of polysubstituted pyrroles.     

A chiral synthesis of four stereoisomers of 1,3-dimethyl-1,2,3,4-tetrahydroisoquinoline, an inducer of Parkinson-like syndrome

Four stereoisomers of 1,3-dimethyl-1,2,3,4-tetrahydroisoquinoline, an inducer of Parkinson-like syndrome, were synthesized by applying a new method of 1,2,3,4-tetrahydroisoquinoline (TIQ) synthesis utilizing the Pummerer reaction as a key step. The chiral centers at C-1 and C-3 were constructed by two routes starting from alaninol (3) and 1-phenylethylamine (4) as a chiral source. Enantiomerically pure 1,3-dimethyl-TIQs (1R,3S)-(2) [corrected], (1S,3R)-(ent-2) [corrected], (1S,3S)-(1) [corrected], and (1R,3R)-(ent-1) [corrected] were prepared in a stereochemically unambiguous manner from 3 in 11 steps (route I) and from 4 in 6 steps (route II). The conformations of tetrahydroisoquinoline ring in 1-methyl, 3-methyl, and 1,3-dimethyl-TIQs were discussed on the basis of their CD, 1H-NMR spectra, and steric energies.     

A novel synthesis of (±)-2-acetyl-5,8-dimethoxy-1,2,3,4-tetrahydro-2-naphthol,a key intermediate for the synthesis of anthracyclinones

The title compound((±)-3) was prepared from readily available 5,8-dimethoxy-3,4-dihydro-2-naphthoic acid(4), according to the novel synthetic route visualized in $\text{Scheme I}$.     

Reactions of 3-acetyl-2-aminotropones and 2-acetyl-7-aminotropones with hydrazine

3-Acetyl-2-aminotropone ( 1a ) reacted with hydrazine to afford its hydrazone ( 3a ) and 3-methyl-1,8-dihydrocycloheptapyrazol-8-one ( 4 ), while methylamino- and pyrrolidinyl-substituted compounds 1b and 1c gave only the cyclized compound ( 4 ). Reactions of 2-acetyl-7-aminotropones 2a-d gave their hydrazones 5a-d and the hydrazone 6 . The hydrazones 3a and 5b were heated in acetic acid to give 4 and 3-methyl-8-methylamino-1,2-diazaazulene ( 7 ), respectively. Several reactions of 4 and 6 were also described.