Oxidative dearomatization/intramolecular Diels-Alder cycloaddition cascade for the syntheses of (±)-atisine and (±)-isoazitine

A convergent and efficient formal synthesis of (±)-atisine has been accomplished. The synthetic strategy is to efficiently construct the bicyclo[2.2.2]octane ring moiety by an oxidative dearomatization/intramolecular Diels-Alder cycloaddition cascade. The first total synthesis of another atisine-type C(20)-diterpenoid alkaloid, (±)-isoazitine, has also been achieved employing the same strategy.     

A concise total synthesis of (±)-minfiensine

A concise total synthesis of (±)-minfiensine using all conventional methods and starting from commercial materials has been completed. The synthesis features a Fischer indole synthesis, a Heck alkylation of an intermediate ketone enolate, conversion of a ketone carbonyl into an epoxide, and transformation of the latter into an allylic alcohol.     

Transannular Claisen rearrangement reactions for the synthesis of vinylcyclobutanes: formal synthesis of (±)-grandisol

Unsaturated eight-membered lactones undergo decarboxylative and non-decarboxylative transannular Ireland-Claisen rearrangement reactions, to give substituted vinylcyclobutanes. A formal synthesis of (±)-grandisol is described.     

(±)Modhephene and (±)isocomene via cascade rearrangement

Dispiro[3.0.4.2] undecane 1 has been synthesized and rearranged to (±)modhephene 2 and triquinane 3 under kinetic control, and to (±)isocomene 4 and triquinane 5 under thermodynamic control. Molecular mechanics calculations (MM2) support the mechanism proposed.     

Total synthesis of (±)-trigonoliimine C via oxidative rearrangement of an unsymmetrical bis-tryptamine

We report the first total synthesis of (±)-trigonoliimine C, a member of a family of structurally complex alkaloids, in 10 steps from tryptamine and 6-methoxytryptamine. Our convergent synthetic strategy relies on a selective oxidative rearrangement of an unsymmetrical 2,2'-bis-tryptamine.     

Intramolecular condensation via an o-quinone methide: total synthesis of (±)-heliol

An acid-catalyzed intramolecular [4 + 2] cycloaddition of a non-natural bisabolene is reported. The key cyclocondensation was developed to access cyclic sesquiterpenes from linear phenolic precursors by generating a reactive o-quinone methide intermediate to initiate a cascade reaction. The new method was applied to the first total synthesis of (±)-heliol.     

An IMDAF cycloaddition approach toward the synthesis of the lycopodium alkaloid (±)-fawcettidine

Using an intramolecular [4 + 2] cycloaddition/rearrangement cascade of 3-(1,4-dioxaspiro[4.4]non-7-en-7-yl)-N-furan-2-ylpropionamide (23) as the key step, the BCD core of the lycopodium alkaloid fawcettidine was constructed. Heating the initially formed Diels-Alder cycloadduct at 180 °C results in a nitrogen-assisted ring opening followed by a deprotonation/reprotonation of the ensuing zwitterion to give a rearranged hexahydroindolinone. Our attempts to induce a related intramolecular furan Diels-Alder reaction (IMDAF) from the corresponding ketone of 23 failed to give any cycloaddition product. Instead, the only product obtained corresponded to a cyclopentenone derivative derived by isomerization of the double bond into the thermodynamically more stable α,β-position. Efforts toward construction of the final skeleton of fawcettidine by ring A closure of the rearranged cycloadduct derived from furanyl amide 23 are discussed.     

General approach for the stereocontrolled synthesis of tricyclic lactones via allene intramolecular cycloaddition. An application to the synthesis of (±)-platyphyllide

A new synthesis of tricyclic lactones via allene intramolecular cycloaddition and its application to synthesis of (±)-platyphyllide are described.     

Allenyl azide cycloaddition chemistry: application to the total synthesis of (±)-meloscine

The pentacyclic alkaloid (±)-meloscine was prepared in 19 steps through a reaction sequence that features a putative azatrimethylenemethane intermediate, generated through cascade cyclization of an allenyl azide substrate, to deliver the core azabicyclo[3.3.0]octadiene substructure. Subsequent manipulation of the peripheral functionality then delivered (±)-meloscine.     

Towards a synthesis of (±)modhephene via cascade rearrangement: Synthesis and rearrangement of dispiro[3.0.4.2]undecanes to [3.3.3]propellanes

The dispiro [3.0.4.2] undecanes 2 and 6 undergo cascade rearrangements yielding the [3.3.3]propellanes 3 and 7, respectively. The rearrangement of 6 proceeds regiospecifically and renders 9 a promising candidate for a direct conversion to (±)modhephene 10.     

A ring-closing metathesis approach for the synthesis of (±)-pregabalin

Abstract  

Efficient utilization of a Mannich-type reaction and the ring-closing metathesis (RCM) approach that leads to a convenient synthesis of 3-(aminomethyl)-5-methylhexanoic acid (pregabalin) is described.     

The ester enolate claisen rearrangement. Total synthesis of (±)-ethisolide

A total synthesis of the mold metabolite ethisolide (1a) is described, wherein a glycolate ester enolate Claisen rearrangement and an acid-induced intramolecular bis-transesterification are key steps.     

Multisubstituted pyrazole synthesis via[3+2]cycloaddition/rearrangement/N-H insertion cascade reaction of α-diazoesters and ynones

The cascade reactions of alkyl α-diazoesters and ynones using Al(OTf)₃ as the catalyst are described.A series of 4-substituted pyrazoles were obtained via [3+2] cycloaddition,1,5-ester shift,1,3-H shift,and N-H insertion process.Deuterium labelling experiments,kinetic studies and control experiments were carried out for the rationalization of the mechanism.     

Total synthesis of the antiviral (±) virantmycin

A total synthesis of the antiviral metabolite virantmycin is described.     

Stereocontrolled synthesis of substituted bicyclic ethers through oxy-Favorskii rearrangement: total synthesis of (±)-communiol E

The potential of the oxy-Favorskii rearrangement to form branched cis-fused bicyclic ethers was explored. Both tertiary and quaternary centers were constructed in highly stereospecific manners. Methanol and primary amines were effective nucleophiles for the rearrangement. The total synthesis of (±)-communiol E was achieved based on this method.     

β-Silyl styrene as a dienophile in the cycloaddition with 3,5-dibromo-2-pyrone for the total synthesis of (±)-pancratistatin

A new synthetic route to (±)-pancratistatin was devised utilizing β-silyl styrene as a dienophile in the cycloaddition with 3,5-dibromo-2-pyrone. The TMS group incorporated in the cycloadduct permitted a facile elimination process for the eventual installation of the C(1)-OH function. Subsequent transformations including Curtius rearrangement and Bischler-Napieralski reactions completed the total synthesis of (±)-pancratistatin.     

First synthesis of (±)-pseudohygrophorone A12, an anti-fungal cyclohexenone derivative isolated from Hygrophorus abieticola

Pseudohygrophorones A¹² and B¹² are cyclohexenone derivatives isolated from Hygrophorus abieticola (Basidiomycete) as anti-phytopathogenic compounds. In this study, the first synthesis of (±)-pseudohygrophorones A¹² is reported, utilizing Michael–aldol cascade reaction for constructing the 3,3-dimethyl-2,4-dioxabicyclo[3.1.1]nonan-9-one skeleton and the diastereoselective addition of alkyllithium to the one-side blocked ketone as the key steps.