Intramolecular formal aza-[3 + 3] cycloaddition approach to indoloquinolizidine alkaloids. A stereoselective total synthesis of (+/-)-tangutorine

[reaction: see text] A 19-step stereoselective total synthesis of (+/-)-tangutorine is described here. The total synthesis features an intramolecular aza-[3 + 3] formal cycloaddition strategy and also a Heck coupling for constructing the C2-C3 bond. This work provides a novel approach toward the indoloquinolizidine family of alkaloids.     

A fast assembly of pentacyclic benz[f]indolo[2,3-a]quinolizidine core by tandem intermolecular formal aza-[3 + 3] cycloaddition/Pictet-Spengler cyclization: a formal synthesis of (+/-)-tangutorine

We have described a concise construction of the pentacyclic benz[f]indolo[2,3-a]quinolizidine intermediate 3 (with an overall yield of 54% for three steps), featuring a tandem intermolecular formal aza-[3 + 3] cycloaddition/Pictet-Spengler cyclization. The present work can be considered as a formal synthesis of beta-carboline alkaloid (+/-)-tangutorine. Our strategy disclosed herein constitutes a new effective general synthetic approach toward the indoloquinolizidine family of alkaloids.     

A Novel Synthesis of Berbines- Condensation of 2-(3,4-Dimethoxyphenyl) Ethyl Bromide with 1,4-Dihydro-6,7-Dimethoxy-3 (2H) Isoquinolone-Synthesis of (+)-Xylopinine

Recently we reported an efficient synthesis of the berbine alkaloids^3,4 by the use of the bromo esters⁵ prepared from 3-isochromanones. Now a new general synthetic route to the berbine alkaloids beginning with the condensation of the phenethylbromide 3 and 3-(2H) isoquinolone 2 is being described. The method gains added advantage of placing desired substitution on both rings A and D of the berbine, emerging from the easy availability of the starting compounds. In conclusion, the present results have not only added one more efficient example to more than a dozen successful procedures of the berbine synthesis⁶ but also offer a potential route to the structurally parallel indoloquinolizidine alkaloids.     

Structure and total synthesis of deplancheine,a novel indoloquinolizidine alkaloid

The structure of deplancheine $\text{5}$, an indoloquinolizidine alkaloid of a novel type, has been established from its spectral properties and also by an orginal synthesis.     

A Novel Synthesis of the Yohimbane Skeleton-Course of the Synthesis of 15,16,17,18,19,20-Hexadehydroyohimbane by Use of Palladium Catalyzed Insertion of Carbon Monoxide

In the course of our continuing synthetic experiments on benzoquinolizidine² and indoloquinolizidine alkaloids³, we have recently utilized palladium catalyzed amidation⁴ for the synthesis of the berbine alkaloids⁵. In this present paper we wish to report, what we believe is the first successful utilization of the palladium catalyzed amidation for the synthesis of the hexadehydroyohimbane skeleton.     

Vallesiachotamine Models

A general synthesis of the indoloquinolizidine nucleus of the indole alkaloids of the yohimboid and corynanthoid types is based on the partial hydrogenation of the β-(3-indolyl-) ethyl salt of a nicotinic ester (e.g. 1a) and the decarboalkoxylative cyclization of the resultant 1, 4, 5, 6-tetrahydropyridine derivative.³ This scheme necessitates the prior preparation of a nicotinic acid with proper C(4) or C(4)/C(5) substituents and limits the last step to carbon-carbon bond formation between the indole a site and the nicotinic ester C(2) position. The following two-step reaction sequence represents a conceptually alternate strategy of indole alkaloid synthesis, designed especially for the construction of vallesiachotamine (2)⁴ and involving introduction of a C(4) pyridine substituent in the first step and cyclization at the C(6) pyridine site in the second step of the two-stage operation.     

New alkaloids from Phoebe grandis (Nees) Merr

The alkaloidal extract of the leaves of Phoebe grandis (nees) merr. have provided two new minor alkaloids; phoebegrandine D (1), a proaporphine-tryptamine dimer, and phoebegrandine E (2), an indoloquinolizidine. This is the first report on the occurrence of an indoloquinolizidine in the Phoebe species. The crude extract also exhibited antiplasmodial activity (IC50<8 microg mL-1). The structures of the novel compounds were elucidated by spectroscopic methods, notably 2D NMR and HRMS.     

Scandium(III)-zeolites as new heterogeneous catalysts for imino-Diels-Alder reactions

This study demonstrates the first zeolite-catalyzed synthesis of piperidine derivatives, including peptidomimetics and indoloquinolizidine alkaloids. The approach developed utilizes a highly effective one-pot reaction cascade, through imine formation and imino-Diels-Alder reactions, promoted by scandium-loaded zeolites as a heterogeneous catalyst. The methodology described benefits from very low catalyst loadings (≤5?mol?% of Sc(III) ), commercially and readily available starting materials, and mild reaction conditions. Furthermore, the Sc(III) -zeolite catalyst can be readily reused more than 10 times without any loss in efficiency.     

Chemistry of 3-(1H-Indol-3-yl)-3-oxopropanenitrile

This review highlighted the methods used for the synthesis of different heterocyclic compounds derived from 3-(1H-indol-3-yl)-3-oxopropanenitrile. The reactivity and their synthetic importance were investigated. In this context, recent progress in the synthesis and use of 3-(1H-indol-3-yl)-3-oxopropanenitrile as precursors for heterocyclic compounds is reviewed.     

Solution-phase synthesis of a combinatorial library of 3-[4-(coumarin-3-yl)-1,3-thiazol-2-ylcarbamoyl]propanoic acid amides

The parallel solution-phase synthesis of a new combinatorial library of 3-[4-(R1-coumarin-3-yl)-1,3-thiazol-2-ylcarbamoyl]propanoic acid amides 9 has been developed. The synthesis involves two steps: 1) the synthesis of core building blocks - 3- [4-(coumarin-3-yl)-1,3-thiazol-2-ylcarbamoyl]propanoic acids, 6 - by the reaction of 3-(omega-bromacetyl)coumarins 1 with 3-amino(thioxo)methylcarbamoylpropanoic acid (5); 2) the synthesis of the corresponding 3-[4-(coumarin-3-yl)-1,3-thiazol-2-yl- carbamoyl]propanoic acids amides 9 using 1,1'-carbonyldimidazole as a coupling reagent. The advantages of the method compared to existing ones are discussed.     

Synthesis and absolute configuration of (-)-meridinol and (-)-3-epimeridinol

The first synthesis of (-)-meridinol and (-)-3-epimeridinol was accomplished from (S)-malic acid. This synthesis unambiguously established the absolute stereochemistry of meridinol.     

Scandium(III)‐Zeolites as New Heterogeneous Catalysts for Imino‐Diels–Alder Reactions

This study demonstrates the first zeolite‐catalyzed synthesis of piperidine derivatives, including peptidomimetics and indoloquinolizidine alkaloids. The approach developed utilizes a highly effective one‐pot reaction cascade, through imine formation and imino‐Diels–Alder reactions, promoted by scandium‐loaded zeolites as a heterogeneous catalyst. The methodology described benefits from very low catalyst loadings (≤5 mol % of Sc^III), commercially and readily available starting materials, and mild reaction conditions. Furthermore, the Sc^III‐zeolite catalyst can be readily reused more than 10 times without any loss in efficiency.     

Synthesis of Conjugated Systems Based on 3-(5-Methylfur-2-yl)-2-(3-oxobutyl)benzofurans

Methods were developed for the synthesis of 3-butyl-2-(3-oxobutenyl)benzofurans and 3-(3-furylbenzofuran-2-yl)acrylic acids on the basis of 3-furyl-2-(3-oxobutyl)benzofurans.     

(R)-2-{[4-(3-甲氧基丙氧基)-3-甲基吡啶-2-基]甲基亚硫酰基}- 1H-苯并咪唑的合成

以2,3-二甲基吡啶为起始原料, 经过11步反应, 不对称合成了质子泵抑制剂的关键中间体: (R)-2-{[4-(3-甲氧基丙氧基)-3-甲基吡啶-2-基]甲基亚硫酰基}-1H-苯并咪唑. 研究了用手性高效液相色谱拆分对映体、测定产品光学纯度的方法, 结果表明目标产品的ee值达到99%. 通过IR, UV, MS以及1H NMR分析对重要中间体和目标产品进行了结构鉴定.     

19-失碳-1α, 25-二羟基维生素D~3A环合成子的合成

报道以价廉、易得的D-(-)-奎尼酸为手性源,经9步反应,有效地合成光学活性的19-失碳-1α,25-二羟基维生素D~3A环合成子4的合成方法。     

Novel Synthesis of 5-Amino-3-bromo-1-(tert-butyl)-1H-pyrazole-4-carbonitrile: A Versatile Intermediate for the Preparation of 5-Amino-3-aryl-1-(tert-butyl)-1H-pyrazole-4-carboxamides

A simple, novel, and efficient route for the synthesis of 5-amino-3-aryl-1-(tert-butyl)-1H-pyrazole-4-carboxamides 1 has been devised. Preparation of pyrazole bromide 3 from potassium tricyanomethanide can be accomplished in only two steps in good yield and features a selective Sandmeyer reaction on the corresponding diaminopyrazole. This allows for a more versatile synthesis of 5-amino-3-aryl-1-(tert-butyl)-1H-pyrazole-4-carboxamides 1 than was previously possible.     

DIASTEREOSELECTIVE SYNTHESIS AND STEREOCHEMISTRY OF (Z)-1-[3-ARYL-2-(PHENYLSULFANYL)-2-OXIRANYL]-1-ETHANONES

Diastereoselective synthesis of a series of (Z)-1-[3-aryl-2-(phenylsulfanyl)-2-oxiranyl]-1-ethanones was effected from the reaction of (Z)-4-aryl-3-(phenylsulfanyl)-3-buten-2-ones with alkaline hydrogen peroxide in tetrahydrofuran. The stereochemistry of the oxiranes has been deduced from two-dimensional NOESY spectrum.     

Pd-catalyzed synthesis of 3-(diarylmethylene)-2-oxindoles and 3-(arylmethylene)-2-oxindoles

An efficient method for the stereoselective synthesis of 3-(diarylmethylene)-2-oxindoles and 3-(arylmethylene)-2-oxindoles via carbopalladation is described. In this approach, an Ugi-4-component reaction (4-CR) adduct was used as the starting material. A one-pot sequence involving intermolecular carbopalladation C-H activation/C-C bond formation efficiently afforded the oxindole derivatives.     

The efficient synthesis of 3-[6-(substituted)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazol-3-yl]-1H-indazole

This study presents an efficient synthesis of 3-[6-(substituted-phenyl)-[1,2,4]triazolo[3,4-b][1,3,4] thiadiazol-3-yl]-1H-indazole via dehydrative condensation with cyclization of 4-amino-5-(1H-indazol-3-yl)-4H-[1,2,4]triazole-3-thiol and fluorinated or nonfluorinated carboxylic acids in presence of phosphorous oxychloride. The multistep reaction pathway proceeds through different compounds. Present synthesis has the advantages of easily accessible starting materials, convenient synthesis, simple reaction condition, wider substrate scope, and higher yield (75% to 90% isolated).     

Enantioselective Syntheses of Heteroyohimbine Natural Products: A Unified Approach through Cooperative Catalysis

Alstonine and serpentine are pentacyclic indoloquinolizidine alkaloids (referred to as “anhydronium bases”) containing three contiguous stereocenters. Each possesses interesting biological activity, with alstonine being the major component of a plant‐based remedy to treat psychosis and other nervous system disorders. This work describes the enantioselective total syntheses of these natural products with a cooperative hydrogen bonding/enamine‐catalyzed Michael addition as the key step.