A new approach to the synthesis of cyclic ethers via the intermolecular allylation of α-acetoxy ethers and ring-closing metathesis

A concise synthesis of the isolaurepinnacin skeleton 6 was achieved via the intermolecular allylation of the α-acetoxy ether 3 followed by ring-closing metathesis. This methodology was successfully applied to the convergent synthesis of the oxocene 15, an advanced synthetic intermediate for the total synthesis of laurencin.     

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.     

A chemoenzymatic approach to the synthesis of the stereoisomers of a β-adrenergic receptor antagonist

The four stereoisomers of Δ²-isoxazoline 2, a β-adrenergic receptor antagonist structurally related to Falintolol 1, were prepared by an enzyme-catalyzed kinetic resolution of the unsaturated secondary alcohol (±)-7 followed by its cycloaddition to pyruvonitrile oxide. Through this strategy, diastereomeric aminoalcohols (+)-2a/(−)-2b and (−)-2a/(+)-2b were obtained in 99 and 92% enantiomeric excess, respectively. The absolute configuration to the target compounds was assigned via chemical correlation to the enantiomers of epoxides 4a and 4b, whose stereochemistry had been previously established.     

Catalytic enantioselective synthesis of azacycloalkenes via intermolecular rhodium carbenoid C–H insertion/ring-closing metathesis sequence

Enantiomerically enriched cyclopropanes and products of C–H insertion reactions were obtained in excellent combined yields and enantioselectivities as a consequence of rhodium-catalyzed decomposition of vinyl diazoacetate in the presence of tert-butoxycarbonyl-(Boc)-protected amines as trapping agents. A series of enantiomerically enriched six- to eight-membered nitrogen-containing heterocycles were subsequently prepared via ring-closing metathesis of the dienes catalyzed by ruthenium benzylidene complex.     

Syntheses of the four stereoisomers of Phytophthora mating hormone α2 and a concise synthesis of mating hormone α1

Four stereoisomers of Phytophthora mating hormone α2 were synthesized using both enantiomers of citronellol as starting materials. The absolute configuration of the natural product was determined to be 7S,11R,15R by oospore-inducing assays of the synthetic isomers. A concise synthetic procedure of α1 was also established using a common synthetic intermediate of α2.     

A new approach to the synthesis of α-chlorocycloalkanones

α-Chlorocycloalkanones(Ⅳ) were synthesized from cycloalkanones via potassiumα-oxocycloalkylsulfonates(Ⅱ).A two-step mechanism was proposed to explain the formation ofⅣfromⅡ.     

A modular approach to α,β-unsaturated N-aryl ketonitrones

A modular approach to α,β-unsaturated N-aryl ketonitrones has been developed. Specifically, condensation of anilines and enals followed by alkylation of the resulting α,β-unsaturated imines provided N-allyl anilines, which were subjected to oxidation with Oxone® to form α,β-unsaturated N-aryl ketonitrones. This modular approach is general and provides rapid access to diversely substituted α,β-unsaturated N-aryl ketonitrones with a single purification step in good yields.     

A biomimetic approach to sporidesmins. synthesis of an α,β-epoxytryptophan derivative

The reaction of 19 - prepared efficiently from 16 - with DDQ affords 22. This epoxide may serve as a model compound to investigate the biosynthesis of sporidesmins, e.g. 1 and 2.     

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.     

An approach to the synthesis of α-l-fucopyranosyl phosphoric mono- and diesters via phosphite intermediates

The reagent chloro-β-cyanoethyl-N,N-diisopropylamino-phosphoramidite reacts smoothly with the anomeric hydroxyl group of a properly protected (benzyl) α-L-fucopyranose to afford a relatively stable phosphite intermediate in high yield. The latter can easily be converted into valuable α-L-fucopyranosyl phosphoric mono- and diesters.     

Novel approach to the synthesis of aliphatic and aromatic α-keto acids

A new practical and efficient synthesis of α-keto acids was accomplished starting from the synthon 1,4-diacetylpiperazine-2,5-dione. The synthesis encompasses both aromatic and aliphatic substrates proving to be versatile and innovative with excellent carbon economy and recycling of the glycine by-product.     

Asymmetric synthesis of allylic secondary alcohols: a new general approach for the preparation of α-amino acids

A new general approach for the synthesis of optically active α-amino acids has been developed. The key steps involve a ruthenium catalysed cross-coupling reaction to give a range of α,β-unsaturated ketones, which were then reduced to allylic secondary alcohols in the presence of a chiral CBS oxazaborolidine. A thermal Overman rearrangement was used to prepare a series of allylic trichloroacetimidates and these were converted under standard conditions to the target α-amino acids in good overall yields.     

A stereocontrolled synthesis of a novel prostacyclin analog “allene-carbacyclin”. Application of molecular mechanics calculations to organic synthesis.

The synthesis of a novel Prostacyclin/Carbacyclin analog 1a has been achieved in a stereocontrolled manner starting from the readily available bicyclic ketone 3. A key strategic feature of the synthesis is a nucleophilic acetylide anion addition to 3, the stereochemistry of which is predicted by MM2 calculations.     

Asymmetric halogenation of chiral imide enolates. A general approach to the synthesis of enantiomerically pure α-amino acids.

The chiral N-acyl oxazolidones 2, as the derived dibutyl boron enolates, have been demonstrated to undergo diastereoselective bromination and subsequent azide displacement to give the α-azido carboximides 4a (5 cases). These adducts may be hydrolyzed under mild conditions to the enantiomerically pure α-azido carboxylic acids 5a.     

Synthesis of a new fluorescent macrocyclic α-amino acid derivative via tandem cross-enyne/ring-closing metathesis cascade catalyzed by ruthenium based catalysts

A simple methodology to a unique macrocyclic α-amino acid (AAA) derivative involving three step synthetic sequence has been reported. In addition, various ruthenium based catalysts were studied to enhance the selectivity of the desired macrocyclic AAA derivative 6. The fluorescence behavior of these AAA derivatives 5 and 6 indicate their potential applications in biological sciences as biomarkers, ion sensors and peptidomimetics.     

Efficient three-step sequence for the deamination of α-aminoesters. Application to the synthesis of CysLT1 antagonists

A practical and efficient three-step sequence for the deamination of α-aminoesters is reported. This method is based on the NaBH₄-mediated selective reduction of α-diazoesters to α-hydrazonoesters and has been successfully applied to the deamination of several representative α-aminoesters including some l-cysteine ethyl ester derivatives, key intermediates in the synthesis of a series of CysLT1 antagonists.