Total Synthesis of (±)-Boschnialactone and (±)-Tetrahydroanhydrodesoxyaucubigenin

A total synthesis of (±)-boschnialactone ( 1 ) and (±)-tertahydroanhydrodesoxyaucubigenin ( 2 ) is described and trisubstitued cyclopentenoid 3 is a key intermediate.     

Total Synthesis of (±)‐Boonein

A total synthesis of (±)‐boonein ( 8 ) from bicyclo[2.2.1]ketone 9 is described. Bicyclo[3.2.1]lactone 10 is the key intermediate.     

Sequential pericyclic reaction of ene-diallene: synthesis of (±)-estrone

The one-pot construction of perhydrophenanthrene from an acyclic substrate was achieved via a sequential pericyclic reaction, which involved the in situ generation of ene-diallene species due to Myers' propargyl alcohol-allene transformation. The resulting perhydrophenanthrene derivative could be successfully converted into (±)-estrone.     

Formal total synthesis of (±)-magellanine

Formal total synthesis of magellanine is described. Key features in the synthesis were stereoselective Ireland-Claisen rearrangement and intramolecular Pauson-Khand reaction of exo-cyclic enynes.     

Bicyclo[3.2.1]octenones as Building Blocks in Natural Product Synthesis (IV): Formal Synthesis of (±)-Hydroxyloganin Aglucone

A formal synthesis of (±)-hydroxyloganin aglucone from bicyclo[3.2.1]octenone 1 is described. Ring opening of syn-8-(methanesulfonyloxy)-1-phenylthiotricyclo[4.2.1.0^3,7]non-4-en-2-one 14 with potassium hydroxide is the key reaction.     

Formal synthesis of (±)-indolizidine 209B

A new method for the synthesis of cis-C-8 methylated indolizidines and quinolizidines has been developed. Straightforward transformations including an isomerization to the trans configuration led to a formal synthesis of (±)-indolizidine 209B.     

Preparation and Structure of di-<Emphasis Type="Italic">exo</Emphasis>-Condensed Norbornane Heterocycles

Summary. Cyclization of di-exo-aroylnorbornanecarboxylic acid with bidentate nucleophiles (hydrazine, o-phenylenediamine, o-aminophenol, alkylenediamines, and amino alcohols) yielded heterotri-, tetra-, and pentacycles. Their structures were established by means of NMR spectroscopy, with the application of HMQC, HMBC, DEPT, DIFFNOE, and COSY methods.     

Zur Synthese vonendo-konfigurierten Isocamphanderivaten

The syntheses of 46endo-configurated isocamphane derivatives starting from camphenilanic acid (1) are described. Theendo-configuration of the new compounds at position 2 of the bicyclus was retained throughout as has been established by¹H-NMR spectroscopy.

     

Rh(I)-catalyzed ring-closing reaction of allenynes: selective construction of cycloheptene, bicyclo[5.3.0]decadienone, and bicyclo[5.2.0]nonene frameworks

Highly selective formation of cycloheptene, bicyclo[5.3.0]decadienone, and bicyclo[5.2.0]nonene skeletons from tri- and tetrasubstituted allenynes has been achieved via a Rh(I)-catalyzed ring-closing reaction and proper choice of substrate and/or reaction conditions.     

Total synthesis of (±)-tangutorine and chiral HPLC separation of enantiomers

The first total synthesis of racemic tangutorine, a novel indole alkaloid, was performed in 7 steps. The key reactions, dithionite reduction and acidic cyclization provided easy access with good yields to the tangutorine skeleton. Comprehensive NMR spectroscopic data of new compounds are given. Chiral HPLC separation of enantiomers is reported.     

Formal synthesis of (±)-cladoniamide G

The formal synthesis of (±)-cladoniamide G, a natural product that exhibits cytotoxicity against human breast cancer MCF-7 cells, is presented. Our strategy employed a Suzuki–Miyaura coupling to join the two indole subunits of this natural product.     

The total synthesis of (±)-arisugacin A

A 20-step total synthesis of (±)-arisugacin A with an overall yield of 2.1% is described here in detail. This synthesis features a formal [3+3] cycloaddition reaction of α,β-unsaturated iminium salts with 6-aryl-4-hydroxy-2-pyrones through a highly stereoselective 6π-electron electrocyclic ring-closure of 1-oxatriene. A strategic dihydroxylation-deoxygenation protocol leading to the desired angular C12a-OH was developed to serve as a critical step in leading to the final total syntheses of arisugacin A. This synthetic endeavor also led to an interesting and unexpected retro-aldol-aldol sequence in the AB-ring.     

Stereoselective total synthesis of (±)-α-vetispirene, (±)-hinesol, and (±)-β-vetivone based on a Claisen rearrangement

The stereoselective total syntheses of (±)-α-vetispirene, (±)-hinesol, and (±)-β-vetivone were accomplished based on a Claisen rearrangement in an alkenyl bicyclic dihydropyran system. The most striking feature of this approach is that the Claisen rearrangement of bicyclic dihydropyran proceeds stereoselectively to provide a multi-functionalized spiro[4.5]decane, which is an efficient precursor for the synthesis of the vetivane sesquiterpenes.     

Concise synthesis of the core bicyclo[2.2.2]diazaoctane ring common to asperparaline, paraherquamide, and stephacidin alkaloids

A versatile synthesis of the bicyclo[2.2.2]diazaoctane core structure of asperparaline, brevianamide, paraherquamide, and stephacidin natural products is demonstrated. This convergent synthesis relies on an intramolecular hetero Diels-Alder reaction to construct the key tetracycle from a diketopiperazine derived azadiene; which in turn was formed from prolinamide and a pyruvic acid derivative. The stereochemical outcome of the Diels-Alder reaction was found to favor the brevianamide stereochemistry.     

Formal synthesis of (±)-brazilin and total synthesis of (±)-brazilane

A convergent synthesis towards (±)-brazilin and (±)-brazilane has been reported from 3,4-dimethoxy benzaldehyde in <15 reaction steps. Palladium(II)-catalysed intramolecular Friedel–Crafts cyclisation and Lewis acid supported intermolecular Friedel–Crafts alkylation reactions have been demonstrated. A tetracyclic substituted indane common key intermediate is employed to furnish the desired two molecules in good to excellent yield. Pd(OH)₂ has played a crucial role in the total synthesis of (±)-brazilane.     

Unusual reactivity of bicyclo[2.2.1]heptene derivatives during the ozonolysis. Part 2

The ozonation of four bornene derivatives, prepared from (R)-(+)-pulegone, which possess a particularly hindered double bond, led to the formation of unexpected products depending on the nature of the solvent. The formation of the corresponding epoxides, ketones with the same skeleton, various lactones and even an allyl alcohol and an allyl chloride (allylic functionalisation) was observed. In two cases, products presenting a pulegone modified skeleton resulting from a Wagner-Meerwein rearrangement were obtained. The structure of three products was confirmed by crystallographic X-ray analysis. Mechanisms taking into account the rigid and congested structure of the reactants explain these results. The most striking steps were backed up by theoretical calculations.     

Synthesis of (±)-cartorimine

Heating pyranulose 4 and cinnamate 2 in the presence of 2,6-di-t-butylpyridine in CH₃CN afforded the [5+2] cycloadduct, which was hydrolyzed to give 13% of cartorimine (1).     

Formal total synthesis of (±)-cortistatin A

A second-generation synthesis of the pentacyclic core of the cortistatins, a family of rearranged steroidal alkaloids that have recently attracted much attention, is reported. The improved sequence provides access to significant quantities of this key compound, which enabled a formal total synthesis of (±)-cortistatin A by conversion to the key Nicolaou/Hirama dienone. It is anticipated that this new, robust route to the pentacyclic core will facilitate the total synthesis of a range of natural products in the cortistatin family, as well as the construction of key structural analogs to probe the promising biological activity of these important compounds.     

Formal total synthesis of (±)-martinellic acid

A concise formal total synthesis of the pyrrolo[3,2-c]quinoline containing natural product, martinellic acid, has been achieved from a pyrroloquinol-2-one through addition of a copper acetylide to an iminium ion. Global deprotection and alkyne reduction then provides the tricyclic triamine, which can be converted to martinelline and martinellic acid.     

Formal and total synthesis of (±)-cycloclavine

A ring fragmentation and intramolecular azomethine ylide 1,3-dipolar cycloaddition sequence of reactions was successfully used in the preparation of a known (±)-cycloclavine precursor in good overall yield. Results of efforts to incorporate the tetrasubstituted cyclopropane ring present in cycloclavine are also discussed.