Investigation of a flexible enantiospecific approach to aziridines

A flexible approach to functionalized and enantioenriched aziridines has been developed from an intermediate aziridinylmethyl tosylate. This protocol features a Cu-catalyzed Grignard substitution reaction that allows a range of functionalized organic fragments to be incorporated. Moreover, a convenient one-pot procedure is outlined that allows the trityl group to be exchanged for a range of common N-protecting groups.     

Zizaane sesquiterpenes. Synthesis of the coates-sowerby tricyclic ketone

The cycloadduct (5) , which is conveniently prepared by irradiation of (4), is converted $\text{via}$ a 4-step sequence, into the tricyclic ketone (2$\text{a}$) and its epimer (2$\text{b}$); the sequence formally completes a new total synthesis of (±)-zizaene (1) and its Me-epimer.     

An approach to forskolin an efficient synthesis of a tricyclic lactone intermediate

Tricyclic lactone 10, a potential intermediate for the synthesis of forskolin, was prepared from (±)-3-hydroxycyclocitral employing an intramolecular Michael addition as the key step.     

An enantiospecific synthesis of estrone

Efficient ring cleavage of 9,10-dibromocamphor (3) provides a monocyclic hydroxyacid (5) which can serve as an intermediate in a new enantiospecific synthesis of estrone.     

An approach to the tricyclic core of madangamines based upon a biogenetic scheme

[reaction: see text] A short synthesis of intermediates possessing the tricyclic core of natural madangamines, bioactive alkaloids found in marine sponges, is described. The key reaction entails the condensation of the sodium salt of diethylacetonedicarboxylate with a dihydropyridinium salt derivative. This new approach is modeled on a biogenetic proposal linking madangamines to ircinals, related alkaloids occurring in sponges of the same order.     

An enantiospecific synthesis of a komarovispirane

The enantiospecific total synthesis of a komarovispirane, containing the complete carbon framework, trans-bicyclo[4.3.0]nonanespiro[8.1′]cyclohexane, of the spiroditerpene komarovispirone, starting from the readily available campholenaldehyde is described.     

General and efficient synthetic approach to novel tricyclic spiroketones

A general and efficient synthetic approach to tricyclic spiroketones of interest as useful scaffolds in drug discovery was developed. Starting from commercially available benzyl 4-oxo-1-piperidinecarboxylate (5), spirocyclic tetralone 4, spirocyclic indanone 14, and spirocyclic benzocycloheptanone 15 were synthesized via six reaction steps in excellent overall yield.     

A novel approach to synthesis of tricyclic diterpenoid

A novel approach has been found and the first total synthesis of (±)-Salvirecognine was accomplished by using it. In which intramolecular cyclization and Friedel-Crafts alkylation took place simultaneously to afford key intermediates for synthesis of aromatic tricyclic diterpenoids.     

The structure of isobarbatene,the stable tricyclic end-point of the bazzanene-barbatene sesquiterpenes

The barbatenes (e.g. 3) and a number of other sesquiterpenes afford a novel rearrangement product on treatment with CF₃CO₂H. This substance, designated isobarbatene, is shown to have structure 6, the result of a bicyclo-[3.2.1]→[2.2.2]→[3.2.1] rearrangement followed by an exo Me shift and deprotonation. The structure assignment is based on spectral and chiroptical data for olefin 6 and its degradation products 8,9 and 10.     

An efficient stereoselective route to the construction of tricyclic core structure towards the synthesis of the sesquiterpenes of the seco-prezizaane family

An efficient stereoselective approach to the construction of a hydrindane derivative having a bridged lactone is described toward the synthesis of the sesquiterpenes of the seco-prezizaane family. The key step involves RO-RCM of a norbornene derivative.     

Development of a flexible approach to Nuphar alkaloids via two enantiospecific piperidine-forming reactions

In this paper we describe the stereoselective synthesis of functionalized lactam 7 via two enantiospecific piperidine-forming techniques and its employment in a general synthetic approach to Nuphar alkaloids. Specifically, the formation of piperidine 18 by formal [3 + 3] cycloaddition and stepwise annelation processes is described; the latter technique was found to be significantly more efficient than the Pd-catalyzed TMM addition process. Finally, exploitation of the exocyclic alkene installed in the piperidine-forming reaction in the transformation of 18 to (-)-deoxynupharidine ((-)-2), (-)-castoramine ((-)-3), and (-)-nupharolutine ((-)-4) via intermediate lactam 7 is delineated.     

New anti-bacterial halogenated tricyclic sesquiterpenes from Bornean Laurencia majuscula (Harvey) Lucas

Three new halogenated tricyclic sesquiterpenes, omphalaurediol (1), rhodolaurenones B (2) and C (3) were isolated together with nine known haloganated sesquiterpenes such as rhodolaurenone A (4), rhodolaureol (5), isorhodolaureol (6), (?)-laurencenone D (7), elatol (8), (+)-deschloroelatol (9), cartilagineol (10), (+)-laurencenone B (11) and 2-chloro-3-hydroxy-α-chamigren-9-one (12) from a population of Bornean red algae Laurencia majuscula. The structures of three new metabolites were determined based on their spectroscopic data (IR, 1D and 2D NMR, and MS). These compounds showed antibacterial activity against three human pathogenic bacteria (Escherichia coli, Salmonella typhi and Vibrio cholera).     

Key tricyclic synthetic intermediates for the preparation of the sesquiterpenes α- and β-cedrene

A completely novel and direct route towards the synthesis of the natural sesquiterpenes α-cedrene and β-cedrene delivered the compounds (3β,3aβ,7β)-(±)-6,6-ethyl­ene­dioxy-3,8,8-tri­methyl-2,3,3a,4,5,6,7,8-octa­hydro-3a,7-methano­azulen-2-one, C₁₆H₂₂O₃, and (3β,3aβ,7β,8aα)-(±)-6,6-ethyl­ene­dioxy-3,8,8-tri­methyl-1,2,3,3a,4,5,6,7,8,8a-deca­hydro-3a,7-methano­azulen-2-one, C₁₆H₂₄O₃, at key stages of the preparative programme. Structural elucidation showed the latter compound to have added an H atom to the same face of the cyclo­pentenone ring as that occupied by the methyl substituent, and also allowed correct isomer identification for further reaction.     

An approach to total synthesis of the cylindricine B pyridoquinoline subclass of tricyclic marine ascidian alkaloids

Employing an intramolecular N-acylketiminium ion/olefin hetero Diels-Alder reaction, and a ring closing metathesis of a vinyl chloride as pivotal steps, it is possible to directly access the pyridoquinoline tricyclic ring system of the marine alkaloids cylindrines B and J.     

An enantiospecific synthesis of (+)-hydroxy-exo-brevicomin

A concise enantiospecific synthesis of the pine beetle pheromone (+)-hydroxy-exo-brevicomin was achieved from l-(+)-tartaric acid in high yield. The key step involves the reduction of a keto-Weinreb amide derived from tartaric acid.     

A general, ring closure metathesis based enantiospecific approach to polyfunctional eudesmane, eremophilane and agarofuran sesquiterpenoids

An enantiospecific and stereo- and functional group diversity oriented approach to eudesmane, eremophilane and agarofuran sesquiterpenoids from (−)-carvone has been devised. RCM has been employed as the key reaction to generate the highly functionalized eudesmane framework. Further elaboration of the eudesmane framework to agarofurans and biogenetic-type rearrangement to eremophilanes is outlined.     

Simple approach to access tricyclic spiro dihydrofurans in a one-pot reaction

A simple and efficient one-pot protocol is accomplished to access tricyclic spiro dihydrofurans (4) by the reaction of β-enamino ketones (1) and dimedone (2) in ethanol followed by sequential addition of N-chlorosuccinimide at ambient temperature for the first time. The selectivity in desired product formation in good yields is the advantage of this protocol.     

Structure elucidation of some highly unusual tricyclic cis-caryophyllane sesquiterpenes from Marasmiellus troyanus

Three new unusual sesquiterpenes (1-3) were isolated from the tropical rainforest basidiomycete, Marasmiellus troyanus and their structure elucidation was achieved by NMR spectroscopy, single-crystal X-ray structural analysis and a modified Mosher’s ester method to determine the absolute stereochemistry of compound 1. These unusual metabolites are probably derived from the caryophyllane class of sesquiterpenes and a possible biosynthetic route to these compounds is proposed. These small natural products represent the best possible features of chemical diversity, being chiral and exhibiting extensive functional group chemistry highlighting the value of natural products as a screening resource for therapeutics discovery programmes.     

Revision of the absolute configuration of the tricyclic sesquiterpene (+)-kelsoene by chemical correlation and enantiospecific total synthesis of its enantiomer

The absolute configuration of the recently identified sesquiterpene (+)-kelsoene was revised by chemical correlation with (R)-(+)-pulegone; the correct structure is (1R,2S,5R,6R,7R,8S)-2,8-dimethyl-6-(1-methylethenyl)tricyclo[5.3.0.0 (2,5)]decane.