Templated scaffolds of cis- and trans-tetrahydrofuran γ-amino acids: γ-azido-β-hydroxy-tetrahydrofuran-2-carboxylates from pentono-δ-lactones

Short syntheses of enantiomeric templated scaffolds of cis- and trans-tetrahydrofuran γ-amino acids from pentono-δ-lactones derived from arabinose and ribose are reported; an unexpectedly efficient synthesis of a templated tetrahydrofuran β-amino acid by azide displacement of a triflate β to an ester function proceeds with remarkably little elimination. These materials should allow evaluation of such peptidomimetics to induce predisposition towards secondary structures.     

Kinetic and thermodynamic aspects in the 1,3-dipolar cycloaddition of five-membered cyclic nitrones to α,β-unsaturated γ- and δ-lactones

The 1,3-dipolar cycloaddition of five-membered ring nitrones to the α,β-unsaturated δ-lactones is kinetically controlled, whereas the same reactions involving γ-lactones, upon heating and prolonged reaction times, display visible reversibility of the reaction and as the consequence, the formation of the more stable, thermodynamic products can be observed. Owing to this and to the high stereoselectivity of the cycloaddition, δ-lactones can be used for kinetic resolution of racemic nitrones whereas γ-ones cannot. In addition the reversibility of the cycloaddition, as well as racemization of 5-substituted 2-(5H)-furanones (γ-lactones), complicates the composition of the post-reaction mixtures and may lead to the formation of partially racemic adducts. The possible asymmetric transformation of cycloaddition involving γ-lactones, which eventually provide the most stable thermodynamic products in high yield, cannot be performed due to the low stability of cyclic nitrones which undergo decomposition.     

氮杂环卡宾催化α,β-不饱和酰氯与亚硝基化合物的[4+2]环化反应

报道氮杂环卡宾催化的α,β-不饱和酰氯与亚硝基化合物的形式[4+2]环化反应合成氮杂-δ-内酯([1,2]嗪-6-酮)化合物.反应机理推测可能是卡宾进攻现场生成的烯基烯酮,得到烯基烯醇负离子,然后与取代的亚硝基苯发生[4+2]环合反应,从而得到的氮杂-δ-内酯产物.     

Copper-catalyzed intermolecular oxidative [3 + 2] cycloaddition between alkenes and anhydrides: a new synthetic approach to γ-lactones

A new copper-catalyzed oxidative [3 + 2] cycloaddition of alkenes with anhydrides using oxygen as the sole oxidant to afford γ-lactones has been developed. This catalyzed cyclization process has a broad substrate scope and affords γ-lactones in good to excellent yields.     

Decarbonylative cycloaddition of phthalic anhydrides with allenes

The decarbonylative cycloadditions of phthalic anhydrides with allenes were performed by using nickel catalyst. The asymmetric variant of the cycloaddition was also achieved by using chiral phosphine ligands to provide δ-lactones enantioselectively.     

Electron-transfer processes : New synthesis of γ-lactones by peroxydisulfate oxidation of isopropylbenzenes and aliphatic carboxylic acids

A new synthesis of γ-lactones by peroxydisulfate oxidation of isopropylbenzenes is described. Evidence concerning the free-radical mechanism is reported; the intermediate formation of alkyl and benzyl radicals is evidenced by trapping them with quinoxaline. The role of the iron catalyst is discussed.     

Synthesis of Spirocyclic and Fused Isoxazoline Building Blocks

A highly efficient multigram synthesis of spirocyclic and fused isoxazoline building blocks is described. Isoxazoline-3-carboxylates were synthesized via a regioselective 1,3-dipolar cycloaddition reaction of 2-chloro-2-(hydroxyimino)acetate and carbo- or heterocyclic alkenes bearing endo- or exocyclic C=C double bonds, resulting in fused or spirocyclic isoxazolines, respectively. The preparation of up to 300 g of these compounds was achieved in a single run. The ester group of isoxazolines was then subjected to common synthetic transformations for the synthesis of corresponding building blocks, including alcohols, chlorides, azides, amines, aldehydes, carboxylic acids, amino acids and their derivatives, difluoromethyl-substituted compounds, and bicyclic γ-lactones. Additionally, a direct cycloaddition-based approach to the synthesis of aminoalkyl- and chloromethyl-substituted isoxazolines was proposed to improve their preparation. The described isoxazoline building blocks are expected to be valuable tools for drug discovery.     

Stereoselective synthesis of 3,4-di-substituted mercaptolactones via photoredox-catalyzed radical addition of thiophenols

A visible light mediated radical addition of thiophenols on 4-phenylbut-3-enoic acids to give diastereoselective synthesis of 3,4-disubstituted γ-lactones is reported. The reaction precludes the conventional prerequisite of conjugate addition. Furthermore, the lactones were successfully utilized in the synthesis of γ-ketoamides.     

Intramolekulare [2+2]-cycloadditionen von γ-oxoketenen

The γ-oxoketenes, which are accessible from methyl 1,3,4-oxadiazin-6-one-2-carboxylate-1 and cycloalkenes, are shown to undergo an intramolecular [2+2] cycloaddition either on heating or on photolysis to give different stereoisomers of β-lactones of the 3-oxo-2-oxabicyclo[2.2.0]hexane-type.     

γ-Lactones as templates in ring-closing metathesis: Enantioselective synthesis of medium sized carbocycles fused to butyrolactones

A methodology for accessing enantiomerically enriched carbocyclic systems fused to γ-lactones is described. Key steps are the stereoselective synthesis of highly substituted γ-lactones and ring-closing metathesis of the suitable ramifications. The process permits the choice of stereochemistry, regioselectivity and ring size of the fused compounds.     

The β-lactone route to α,β-unsaturated δ-lactones. Total syntheses of (±)-goniothalamin and (−)-massoialactone

The HF-induced translactonization of 2′-silyloxy-3-trimethylsilyl-2-oxetanones, obtained through Lewis acid-promoted [2+2] cycloaddition between β-silyloxyaldehydes and trimethylsilylsilylketene, into α,β-unsaturated δ-lactones is applied to the syntheses of (±)-goniothalamin and (−)-massoialactone.     

γ-Lactones from δ-lactones: total synthesis of the biosynthetic derailment product mupirocin H

Two different strategies for the synthesis of functionalised γ-lactones from δ-lactones are described and used in a convergent synthesis of (+)-mupirocin H. The total synthesis is versatile and may be readily adapted for the preparation of further truncated metabolites from Pseudomonas fluorescens.     

Dramatic enhancement of antagonistic activity on vitamin D receptor: a double functionalization of 1alpha-hydroxyvitamin D3 26,23-lactones

The synthesis of novel vitamin D receptor antagonists, 24-methyl-1alpha-hydroxyvitamin D(3) 26,23-lactones, is reported. We found that the biological activities of the vitamin D(3) lactones were affected by the structure of the lactone part. Furthermore, introduction of a 2alpha-methyl group into the 24-methylvitamin D(3) lactones dramatically enhanced their anti-vitamin D activity. [reaction: see text]     

Synthesis of δ-Lactones from Glutaraldehyde

A novel and general synthesis of δ-lactones from glutaraldehyde is described. The dialdehyde is first reacted with an alkyl or substituted alkyl Grignard reagent to afford a δ-hydroxyaldehyde in good yield. These aldehydes exist preferentially in the cyclic hemiacetal form (δ-lactols). Oxidation of the latter compounds to give δ-lactones is readily achieved with silver oxide or bromine. The δ-lactols and δ-lactones serve as intermediates for the total synthesis of steroids.     

Manganese(III)-mediated oxidative free-radical cyclisations of allenyl malonates

The regioselective synthesis of alkenylcyclanones by the oxidative radical cyclisation of malonyl radicals onto both allenes and an allylsilane is reported, along with the diastereoselective formation of [3.3.0]-bicyclic γ-lactones from two of these alkenylcyclanones. Furthermore, the cyclisation of 3-, 4- and 5-allenyl malonates on exposure to manganese(III) acetate under both oxidative and reductive termination conditions is reported.     

Highly Enantioselective Intramolecular 1,3‐Dipolar Cycloaddition: A Route to Piperidino‐Pyrrolizidines

Enantioselective catalytic intermolecular 1,3‐dipolar cycloadditions are powerful methods for the synthesis of heterocycles. In contrast, intramolecular enantioselective 1,3‐dipolar cycloadditions are virtually unexplored. A highly enantioselective synthesis of natural‐product‐inspired pyrrolidino‐piperidines by means of an intramolecular 1,3‐dipolar cycloaddition with azomethine ylides is now reported. The method has a wide scope and yields the desired cycloadducts with four tertiary stereogenic centers with up to 99 % ee. Combining the enantioselective catalytic intramolecular 1,3‐dipolar cycloaddition with a subsequent diastereoselective intermolecular 1,3‐dipolar cycloaddition yielded complex piperidino‐pyrrolizidines with very high stereoselectivity in a one‐pot tandem reaction.     

Bifunctional cinchona alkaloids-catalyzed asymmetric [4+2] cycloaddition reaction of β,γ-unsaturated α-keto esters with oxazolones

A highly enantioselective [4+2] cycloaddition reaction of β,γ-unsaturated α-keto esters with oxazolones was realized with readily available cinchona alkaloids as the catalysts. Using this reaction, a series of highly functionalized δ-lactones with adjacent α-quaternary-β-tertiary stereocenters were obtained in high yields (up to 97%) and with good-to-excellent enantioselectivities (up to 97% ee).     

General synthesis of pyrroloquinolizidines: synthesis of an unnatural homologue of the pyrroloindolizidine myrmicarin alkaloid 215B

A general synthesis approach to pyrroloquinolizidines (3,4,5,5a,6,7,8-heptahydropyrrolo[2,1,5-de]quinolizines) via a münchnone 1,3-dipolar cycloaddition is reported. The approach was applied to the synthesis of an unnatural pyrroloquinolizidine homologue of myrmicarin 215B.     

Regio- and diastereoselectivity studies on the photocycloaddition of ketene diethyl acetal to chiral 2(5H)-furanones

The photochemical [2+2] cycloaddition of 1,1-diethoxyethylene to chiral 2(5H)-furanones is investigated. The effect of the substituents of the lactone and the polarity of the solvents on the chemical yield, regioselectivity, and facial diastereoselectivity is evaluated. The reactions in ether proceed with excellent regioselectivity and good yields. Hydrolysis of the ketal group of the major cycloadducts afforded enantiopure cyclobutanones fused to γ-lactones.     

Efficient synthetic access to the hetisine C20-diterpenoid alkaloids. A concise synthesis of nominine via oxidoisoquinolinium-1,3-dipolar and dienamine-Diels-Alder cycloadditions

A concise synthetic approach to the hetisine C20-diterpenoid alkaloids is reported. The total synthesis of (+/-)-nominine was accomplished in a 15-step sequence employing a dual cycloaddition strategy. Key features of the synthesis include a reversible intramolecular 4-oxidoisoquinolinium betaine dipolar cycloaddition in conjunction with a pyrrolidine-induced dienamine isomerization/Diels-Alder cascade.