Concise synthesis of anhydrovinblastine from leurosine

[reaction: see text] The Cp(2)TiCl-mediated deoxygenation of leurosine (1) afforded anhydrovinblastine (4) in good yield. Furthermore, as the reaction proceeded via a carbon-centered radical intermediate, this transient was also trapped by a hydrogen-atom donor to afford selectively reduced alkaloid 10.     

Straightforward access to new vinca-alkaloids via selective reduction of a nitrile containing anhydrovinblastine derivative

A procedure to exclusively obtain 3′S-cyanoanhydrovinblastine 12 from two naturally occurring vinca-alkaloids (catharanthine and vindoline) in one step with good yield is described. Stereoselective reductions of 12, providing straightforward access to three new vinca-alkaloids, including two diastereomers 3′S-cyano-(4′R,5′-dihydro)-anhydrovinblastine and 3′S-cyano-(4′S,5′-dihydro)-anhydrovinblastine as well as (3′S-aminomethyl)-(4′S,5′-dihydro)-anhydrovinblastine in good yields is also reported.     

Selective deoxygenation of allylic alcohol: stereocontrolled synthesis of lavandulol

Selective deoxygenation of allylic alcohol can be successfully carried out by the formation of alkoxyalkyl ether (EE or MOM), followed by Pd(dppe)Cl(2)-catalyzed reduction with LiBHEt(3). (+)-S-Lavandulol has been efficiently synthesized by the application of this protocol to the diol derived from the Pb(OAc)(4)-promoted oxidative ring-opening of (-)-R-carvone. This deoxygenation method is general and selective for allylic alcohols.     

Selective deoxygenation of gibberellic acid with fluoroarylborane catalysts

Reductive late-stage functionalization of gibberellic acid is reported using three fluoroarylborane Lewis acids; (B(C₆F₅)₃, B(3,5-C₆H₃(CF₃)₂), and B(2,4,6-C₆H₂F₃)₃) in combination with a tertiary silane and a borane (HBCat) reductant. In each case, C–O bond activation occurs, and different products are obtained depending on the reductant and catalyst employed.     

Selective deoxygenation of sulfoxides with thexylchloroborane-methyl sulfide complex

Thexylchloroborane-methyl sulfide complex selectively deoxygenated both aromatic and aliphatic sulfoxides to the corresponding sulfides in high yield and purity at 0° C without affecting some other reducible structures.     

Photoacylations of 2-substituted 1,4-naphthoquinones: a concise access to biologically active quinonoid compounds

Photochemical acylations of 2-substituted-1,4-naphthoquinones with various aldehydes furnished acylated hydroquinones and acylated quinones in moderate to good combined yields. All reactions are easily performed and open a rapid access to biologically active compounds. For the 2-methyl-1,4-naphthoquinone/butyraldehyde pair, a novel tri-keto compound has been additionally isolated.     

A novel and concise synthetic access to chiral 2-substituted-4-piperidone

A novel and concise synthetic access to enantiopure chiral 2-aryl/alkyl substituted 4-piperidone has been demonstrated.This new route features two key steps:the highly diastereoselective conjugate addition of homochiral lithium amides to trans-β-substituted-α,β-unsaturated methyl esters guaranteed the enantiopurity at 2 position(de19:1)and the intramolecular attacking of carbanions to methyl esters led to the formation of the piperidone ring.A wide range of substrates,including chiral2-aryl and 2-alkyl-4-piperidones,were successfully synthesized with modest to high yield.Moreover,some non-chiral3-substituted-4-piperidones were also synthesized with enhanced ring-formation yield,implicating the versatility of this method in construction of various piperidine rings.     

Asymmetric cyclization via memory of chirality: a concise access to cyclic amino acids with a quaternary stereocenter

N-(omega-Bromoalkyl)-amino acid derivatives, readily prepared from natural alpha-amino acids, gave cyclic amino acids with a quaternary stereocenter by treatment with potassium hexamethyldisilazaide in DMF. The chirality of parent amino acids was almost completely preserved during an enolate-formation and cyclization process, giving aza-cyclic amino acids in up to 98% ee in retention of configuration. This method is applicable to the asymmetric synthesis of azetidine, pyrrolidine, piperidine, and azepane derivatives. The asymmetric cyclization seems to proceed via an axially chiral enolate intermediate and not through a concerted SEi process.     

Selective deoxygenation of styrene oxides under a CO atmosphere using silver nanoparticle catalyst

Deoxygenation of styrene oxide derivatives into the corresponding alkenes was efficiently catalyzed by inorganic materials of hydrotalcite-supported silver nanoparticles (Ag/HT) using CO/H₂O as a reductant. The Ag/HT catalyst was reusable without loss of activity or selectivity.     

Laccase-catalyzed coupling of catharanthine and vindoline: an efficient approach to the bisindole alkaloid anhydrovinblastine

The efficient enzyme-catalyzed coupling of the indolic alkaloids catharanthine and vindoline was carried out by exploiting the oxidoreductases laccases and atmospheric oxygen. Following NaBH₄ reduction of the eniminium cationic intermediate, the synthetically useful dimer anhydrovinblastine (AVBL) was isolated and characterized. Several reaction parameters were investigated in detail and, under the optimized reaction conditions, AVBL was isolated in 56% yield. The practicability of this bioconversion was further confirmed through the condensation of catharanthine with the vindoline analogue 11-methoxy-dihydrotabersonine.     

Reaction of oxiranes with lithium: deoxygenation leading to olefins

Mono-, di-, tri- and tetra-substituted epoxides undergo facile deoxygenation yielding olefins when treated with lithium in tetrahydrofuran. Aliphatic epoxides yield olefins with the same stereochemistry as the parent compound.     

Selective deoxygenation of aryl selenoxides by triaryl phosphites. Evidence for a concerted transformation

Triaryl phosphites selectively reduce aryl selenoxides to selenides. The Hammett plot of the reactions of para-phenyl substituted triaryl phosphites with diphenyl selenoxide gave ρ=+2.3, whereas with bis(p-methoxyphenyl) selenoxide, ρ=−2.1. The results are consistent with a concerted mechanism for the oxygen transfer from Se to P.     

Stereospecific deoxygenation of 1,2-diols to olefins

The 2-dimethylamino-1,3-dioxolane derivatives of 1,2-diols when treated with trifluoromethane sulfonic anhydride and diisopropylethylamine in toluene give the corresponding olefins stereospecifically under mild experimental conditions.     

Effective synthesis of negatively charged cyclodextrins. Selective access to phosphate cyclodextrins

We report the selective preparation of α- and β-cyclodextrins bearing one and two phosphate moieties on the primary rim. These compounds were prepared by selective O-debenzylation of fully protected derivatives, followed by phosphorylation and deprotection. The synthesis of an α-cyclodextrin with both, a carboxylic group and a phosphate moiety on primary positions is also described. Title compounds are examples of negatively charged cyclodextrins that might be of interest in studying the complexation of cationic guests.     

Heterogeneous deoxygenation of ketones

Relatively unhindered ketones are converted directly to the corresponding hydrocarbons in the presence of hydrogen at normal pressures and a Ni/Al₂O₃ catalyst in a simple gas-phase reactor.     

Enzyme-catalysed oxygenation and deoxygenation routes to chiral thiosulfinates

Enantioenriched thiosulfinates have been obtained by dioxygenase- and chloroperoxidase-catalysed oxidation of 1,2-disulfides and dimethyl sulfoxide reductase-catalysed deoxygenation.     

A concise route to benzofused macrolactones via ynolides: cycloproparadicicol

A new facile synthesis has been developed for nanomolar Hsp90 inhibitor, cycloproparadicicol (2). Our approach relied on cobalt-complexation promoted RCM, in combination with tandem Diels-Alder/retro-Diels-Alder reactions to assemble the resorcycinylic macrolactone.     

Selective deoxygenation of sugar polyols to alpha,omega-diols and other oxygen content reduced materials--a new challenge to homogeneous ionic hydrogenation and hydrogenolysis catalysis

An oxygen atom on every carbon--this is the problem! While nature provides linear C(3) to C(6) building blocks in the form of sugar alcohols in large and renewable abundance, they are overfunctionalized for the purpose of most chemical applications. Selective deoxygenation by anthropogenic catalyst systems may be one answer to this challenge.     

Gold nanoparticle-catalyzed environmentally benign deoxygenation of epoxides to alkenes

We have developed a highly efficient and green catalytic deoxygenation of epoxides to alkenes using gold nanoparticles (NPs) supported on hydrotalcite [HT: Mg(6)Al(2)CO(3)(OH)(16)] (Au/HT) with alcohols, CO/H(2)O or H(2) as the reducing reagent. Various epoxides were selectively converted to the corresponding alkenes. Among the novel metal NPs on HT, Au/HT was found to exhibit outstanding catalytic activity for the deoxygenation reaction. Moreover, Au/HT can be separated from the reaction mixture and reused with retention of its catalytic activity and selectivity. The high catalytic performance of Au/HT was attributed to the selective formation of Au-hydride species by the cooperative effect between Au NPs and HT.