A synthesis of pyrrolo[2,1-a]isoquinolines through the reaction of activated acetylenes and isoquinoline in the presence of ethyl bromopyruvate

Isoquinoline reacts with ethyl bromopyruvate in the presence of dialkyl acetylenedicarboxylates or diaryloylacetylenes to produce dialkyl 1-(2-ethoxy-2-oxoacetyl)pyrrolo[2,1-a]isoquinoline-2,3-dicarboxylates or ethyl 2-[2,3-diaryloylpyrrolo[2,1-a]isoquinoline-1-yl]-2-oxoacetates in good yields.     

Exploratory studies towards a total synthesis of the unusual bridged tetracyclic Lycopodium alkaloid lycopladine H

A strategy for a total synthesis of the structurally novel Lycopodium alkaloid lycopladine H has been investigated. Key steps that have been tested include: 1. a regioselective Diels-Alder cycloaddition of nitroethylene with an o-quinone ketal to produce the bicyclo[2.2.2]octane moiety of the alkaloid; 2. a stereoselective Henry reaction to generate the requisite functionality and configuration at C-5; 3. a stereoselective catalytic hydrogenation of a trisubstituted alkene to set the C-15 methyl configuration.     

Expedient synthesis of the tetracyclic core of ent-nakadomarin A

An efficient eight-step assembly of the tetracyclic core (ABCD rings) of ent-(+)-nakadomarin A, a bioactive hexacyclic marine alkaloid, has been realized with Sonogashira coupling, platinum(II)-promoted cascade cyclizations, and saturation of a challenging carbon-carbon double bond through a hydroboration/oxidation/xanthate formation/Barton-McCombie deoxygenation sequence as key transformations.     

A short synthesis of (+)-hygrine

The synthesis of the alkaloid hygrine in a series of six steps starting from readily available proline N-methyl derivative (5) is described.     

A facile one-pot synthesis of N-substituted tetrahydroquinolines

An uncatalyzed one-pot synthesis of N-substituted tetrahydroquinolines was achieved in good yields by the reaction of quinoline and alkyl/acyl halides with Hantzsch dihydropyridine ester under mild reaction conditions.     

One-pot multistep synthesis of 3-aminoindolizine derivatives

We have developed an efficient one-pot multistep sequence to the synthesis of 3-aminoindolizine derivatives by using Hantzsch ester (9) as a mild hydride transfer agent. The reaction scope was investigated and the effect of substrates on reaction outcomes was discussed.     

A practical formal synthesis of camptothecin

The synthesis of the DE ring of camptothecin using simple and inexpensive starting materials, employing an addition elimination reaction and selective esterification of an aliphatic carboxylic acid as key steps is described.     

A convenient synthesis of a novel fused tetracyclic heterocoumarin

New tetracyclic 6H‐[1]benzopyrano[3,4‐e]pyrazolo[1,5‐a]pyrimidin‐6‐ones ( 4a‐e ) have been synthesized through the condensation under acidic conditions of [1]benzopyrano[4,3‐c][1,5]‐benzodiazepin‐7(8H)‐one ( 1 ) and a series of 3,4‐disubsituted 5‐amino‐1H‐pyrazoles 3a‐e .     

A chemoenzymatic total synthesis of the Amaryllidaceae alkaloid narseronine

A 15-step and fully stereocontrolled total synthesis of the title alkaloid 1 has been accomplished using the enantiomerically pure and enzymatically-derived cis-1,2-dihydrocatechol 2 as starting material. The final and pivotal step involved the intramolecular hetero-Michael addition of secondary amine 16 to a tethered enone moiety followed by trapping of the resulting enolate through its reaction with an adjacent ester residue.     

Preparation of a functionalized tetracyclic intermediate for the synthesis of rhodexin A

An efficient synthesis of the tetracyclic steroid core, 19, of rhodexin A and sarmentogenin is reported. An initial inverse-electron-demand Diels-Alder reaction of the acyldiene 6 with the silyl enol ether 7a gave the cycloadduct 8 with the required four contiguous stereocenters in a single step. This compound was then transformed into the methylated enedione 13 which afforded after a reductive alkylation and annulation sequence the tetracycle 19.     

A facile approach to the synthesis of securinega alkaloids: stereoselective total synthesis of (−)-allonorsecurinine

A concise stereoselective total synthesis of alkaloid (−)-allonorsecurinine is described utilizing classical reactions such as Grignard, Aldol and Horner-Wittig reactions as the key steps.     

A new approach to the synthesis of indole-and benzofuran-containing tetracyclic condensed systems

A new method is described for the synthesis of the 1H-benzo[b]furoindole heterocyclic systems from the corresponding isomeric amino acids with amino groups at positions 2 and 3. By this method it is possible to obtain these tetracyclic systems not only in the form of one isomer but also to convert them from one to the other. From the tetracyclic systems with angular structure it is possible to obtain the corresponding linear isomers. On the other hand, from the isomer with the linear structure it is possible to change to the isomer with angular fusion of the pyrrole ring. The classical Fischer reaction served as model for such transformations. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1463–1471, October, 2007.     

Daphniglaucin C, a novel tetracyclic alkaloid from Daphniphyllum glaucescens

A novel Daphniphyllum alkaloid with an unprecedented tetracyclic ring system consisting of an octahydroindole and a hexahydroazulene rings, daphniglaucin C (1), has been isolated from the leaves of Daphniphyllum glaucescens and the structure and relative stereochemistry were elucidated on the basis of spectroscopic data. Daphniglaucin C (1) inhibited the polymerization of tubulin.     

A concise synthesis of meridianin F

A concise synthesis of the protein kinase inhibitor meridianin F has been achieved in good overall yield starting from 5,6-dibromoindole-3-carbaldehyde.     

A new and simple method for the synthesis of highly functionalised pyrrolizidines, indolizidines and pyrroloazepines

The reaction of 5-, 6- and 7-membered cyclic thioimidates with cyclopropenones gives access to highly functionalised pyrrolizidines, indolizidines and pyrroloazepines via a formal [3+2] cycloaddition process.     

A short synthesis of koniamborine, a naturally occurring pyrano[3,2-b]indole

An expedient synthesis of the alkaloid koniamborine, the only to date isolated naturally occurring pyrano[3,2-b]indole is presented. The key pyrano[3,2-b]indole forming step is a palladium-catalyzed reductive N-heteroannulation of 2-(4-methoxy-2-nitrophenyl)-(4H)-pyrane-4-one.     

A novel one-pot domino reaction for the synthesis of 2-acetyl-3-(phenylamino)indolizine-1-carboxamide derivatives

2-Acetyl-3-(phenylamino)indolizine-1-carboxamide derivatives were obtained via a one-pot domino reaction of alkyl or aryl isocyanides and pyridine-2-carbaldehyde in the presence of acetoacetanilide in toluene without any prior activation or modification.     

The enantioselective synthesis of tetracyclic methyllycaconitine analogues

A new enantioselective synthesis of ABEF ring analogues of methyllycaconitine has been developed using a chiral cobalt(III) salen-catalyzed Diels-Alder reaction to form the B ring. Subsequent elaboration to form the A, E and F rings was achieved by sequential Dieckmann, Mannich and Wacker-type cyclizations to afford tetracyclic analogues in 97.5% ee.     

Synthetic study of hetisine-type aconite alkaloids. Part 1: Preparation of tetracyclic intermediate containing the C14-C20 bond

Full details for the total synthesis of (±)-nominine, a hetisine-type aconite alkaloid, are presented in three parts. Here (part 1), we describe the preparation of the key tetracyclic intermediate 6. Our palladium-catalyzed intramolecular α-arylation was adopted for preparation of the intermediate 4 with an angular formyl group. An acetal-ene reaction was then employed for C14-C20 bond formation to secure 6 from 5. The reaction mechanism of the acetal-ene reaction is discussed, and a method for removal of the 2-hydroxyethyl group from 6 is developed.