Enantioselective syntheses of diquinane and (cis,anti, cis)-linear triquinanes

The enantioselective syntheses of diquinane and cis, anti, cis-linear triquinanes, starting from the readily available (S)-campholenaldehyde, employing an intramolecular rhodium carbenoid CH insertion reaction, are described.     

Chiral ring a synthons for vitamin d synthesis

A unique approach to vitamin d compounds via chiral bicyclo-[3.1.0]-hexane derivatives is described.     

Enantiospecific synthesis of angular triquinanes

The enantiospecific synthesis of angular triquinanes has been developed starting from the readily available (S)-campholenaldehyde. Two alternate strategies have been used, one employing a Johnson’s orthoester Claisen rearrangement followed by an intramolecular cyclopropanation and regioselective cyclopropane ring cleavage, and a second one based on a RCM reaction.     

Formation of linear triquinanes by serial homolytic cyclisation

Treatment of the trienyl bromide (2) with tributylgermane affords the two stereo-isomers of 4-methyl-$\text{cis,anti,cis}$-tricyclo[6,3,0,0²,⁶] undecane 9 (27%) and related tricyclic compounds by processes involving three consecutive radical ring closures     

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.     

Dilithiated synthons: synthesis of cyclic ethers

Recent advances in the generation of dilithiated synthons by arene-catalyzed lithiation of the corresponding dichloro compounds in the presence of carbonyl compounds (Barbier-type reaction conditions) as the key step are described. Further cyclization of the generated diols under different reaction conditions affords a variety of mono-, bi-, and spirocyclic ethers.     

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.     

System oriented design of triquinanes: stereocontrolled synthesis of pentalenic acid and pentalenene

Pentalenic acid, 5, and pentalenene, 4, and their C-9 epimers 5a and 4a, respectively, were synthesized using [4+1] and [2+3] cyclopentene annulation methodology. The key steps involved internal cyc1opropanation of dienes 23 or cyc1opropanation of enone 25 followed by the thermolytic rearrangements of cyclopropanes 24, 39, 42, 45, and 48 to furnish triquinanes 26 and 40. An investigation of electronic effects affecting the diradical cleavage of viny1cyclopropanes was performed. The triquinanes 26 or 40 were transformed to the title compounds by reductive operations at C-9. The equilibration of esters 60 at C-9 was briefly addressed in the context of molecular mechanics predictions regarding the thermodynamic stabilities of conformations at C-9 in the natural vs. the epi series. The stereoselectivities in approaches to natural hydrocarbons and their C-9 epimers were evaluated as better than 9:1 in each series.     

Phosphafluorenyl lithiums:direct synthesis from white phosphorus,structure and diversified synthons

While rich chemistry of phospholyl anions is discovered,phosphafluorenyl anions are only proposed as the critical intermediates for the synthesis of phosphafluorenes.In this article,we reported the direct synthesis of phosphafluorenyl lithiums from white phosphorus(P₄)through direct P-C bond formation.The reaction between P4 and biphenyl dilithio reagents efficiently afforded phosphafluorenyl lithiums,which were further used to synthesize different kinds of organophosphorus compounds.The aggregation states of phosphafluorenyl lithiums were investigated for the first time.Mechanistic studies by DFT calculations revealed a cooperative nucleophilic attack of two C?Li bonds on P₄molecule.     

Chiral nanopatterned surfaces as versatile enantiospecific adsorbents: a Monte Carlo model

This paper deals with the application of the Monte Carlo simulation method for modeling of adsorption of chiral molecules on a planar surface patterned with active binding sites. The enantiomers are assumed to be rigid chains composed of four identical segments, each occupying one binding site. The energy of interaction between a segment and a binding site is characterized by epsilon(a) and epsilon(b) depending whether the site is active or it is inert. We demonstrate that epsilon(a)>epsilon(b) imposed in our previous work [J. Chem. Phys. 126, 144709 (2007)] is not a necessary condition for the separation of enantiomers form their racemate. The obtained results suggest that the major source of enantioselectivity of the surface lies in its geometrical properties. The active adsorption sites which form the chiral pattern do not have to interact stronger with the adsorbing molecules to ensure enantioseparation. In this context, the proposed chiral surface offers more flexibility in selection of the energetic properties of the binding sites. This, in practice, means wider possibilities of manipulating chemical composition of the surface.     

Facile enantiospecific synthesis of (+)-iso-cladospolide B

Enantiospecific synthesis of bio-active butenolide (+)-iso-cladospolide B from d-(?)-tartaric acid in a short synthetic sequence is presented. Pivotal reaction sequence includes cross metathesis of an alkene and Wittig olefination.     

A biogenetically patterned enantiospecific synthesis of allopupukeanones

The first enantiospecific synthesis of allopupukeanones has been accomplished starting from 6-methylcarvone. A biogenetically patterned rearrangement of a pupukeanane to allopupukeanane was employed as the key step.     

Formal enantiospecific synthesis of (+)-FR900482

The enantiospecific synthesis of FK973, and thus a formal enantiospecific synthesis of the antitumor antibiotic (+)-FR900482, is reported. Addition of aniline 8 to chiral epoxide 9, prepared from l-vinylglycine, afforded amino alcohol 12. After protection of the aliphatic nitrogen with the 9-phenylfluoren-9-yl group, to preserve the acidic stereocenter from racemization, formation of the aziridine 14 and intramolecular condensation under basic conditions gave azocinone 15. Hydroxymethylation at the benzylic position was achieved by a process involving methylenation, epoxidation, and hydrogenolysis; the absolute stereochemistry of the resulting alcohol 23 was determined by X-ray crystallographic analysis. The hydroxyl group of 23 was carbamoylated, and the aromatic amine was deprotected electrochemically and then oxidized to give an unstable hydroxylamine that was immediately protected as acetate 26. Oxidation of 26 with DMP, followed by hydrazinolysis of the acetyl group led to spontaneous closure of the resulting N-hydroxyamino ketone to hemiketal 28, which can be considered as a fully protected precursor of FR900482 and derivatives. Acid treatment to remove the protecting groups and acetylation afforded the triacetate FK973.     

Chiral synthons from α-pinene: enantioselective syntheses of bicyclo[3.3.0] and [3.2.1]octanones

Enantioselective syntheses of bicyclo[3.3.0]octan-3-one, bicyclo[3.2.1]octan-3-one and bicyclo[3.2.1]octan-2-one derivatives were accomplished by employing a chiron based approach, using intramolecular rhodium carbenoid C–H insertion, acid catalysed cyclisation of α-diazo ketone and intramolecular type II carbonyl ene reactions as key steps.     

Aziridines derived from amino acids as synthons in pseudopeptide synthesis

The reactivity of the Z-protected aziridine derived from aspartic acid has been studied with various N- and O-nucleophiles. The optimized reaction conditions allow quick and easy access to 1, 2-diamines or amino alcohols. In the case of opening with N-nucleophiles, very good regioselectivity was observed. Use of an α-amino ester as the nucleophile yielded a methyleneamino pseudodipeptide.     

First enantiospecific synthesis of (+)-β-herbertenol

The first enantiospecific synthesis of (+)-β-herbertenol, from naturally occurring R-(+)-citronellal, employing Taber's diazo decomposition protocol as the key step, is described.     

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.     

The first enantiospecific total synthesis of (+)-seychellene

The first enantiospecific total synthesis of the tricyclic sesquiterpene (+)-seychellene, starting from (R)-carvone via (S)-3-methylcarvone, has been accomplished employing a combination of an intermolecular Michael addition-intramolecular Michael addition sequence and an intramolecular alkylation reaction for the generation of the two vicinal quaternary carbon atoms.     

One-pot synthesis of novel spiro-annelated pyrrole-containing heterocyclic systems from suitable synthons

New tetracyclic systems containing a pyrrolobenzodiazepine 5 or a pyrrolobenzotriazepine 6 moiety bounded by a spiro linkage to the piperidine nucleus are described. They have been synthesized by a simple reaction involving the interaction between proper aromatic amines and 4-oxopiperidines substituted or not at the 1-position in the presence of maleic acid as a catalyst. The synthesis of spiropyrrolo[1,2-a]quinoxaline-2,4′-piperidine 7 and its 1′-acyl derivatives by the same procedure is also reported.