Synthesis of substituted α,β-unsaturated δ-lactones from vinyl tellurides

A new approach for the synthesis of α,β-unsaturated δ-lactones, a unit present in many natural products with interesting biological activities is described. The approach was based on the use of a vinyl telluride, and it is complementary to the methods using ring-closing metathesis. The sequence was performed in good overall yield with retention of the Z-double bond geometry.     

Efficient synthesis of α,β-unsaturated γ-lactones linked to sugars

A series of structurally diverse unsaturated sugar-derived lactones has been prepared. α,β-Butenolides were introduced to the sugar moiety starting from epoxides, while α-methylene-γ-lactones were constructed from a carbonyl precursor, either an aldehyde, a ketone or a lactone. In the last case, an unprecedented Reformatsky-type reaction has been developed.     

Three-component and nonclassical reaction of phosphines with enynes and aldehydes: formation of γ-lactones featuring α-phosphorus ylides

Inverted carbenoid species, generated from attack of phosphines at the α(δ')-carbon of hex-2-en-4-ynedioic acid dialkyl esters, react with aldehydes to give γ-lactones possessing an α-phosphorus ylide moiety.     

Silylene transfer to α-keto esters and application to the synthesis of γ-lactones

Disubstituted α-hydroxy acids have been synthesized by metal-catalyzed silylene transfer to α-keto esters. A range of substituents are tolerated in the transformation with the exception of branched groups at the vinylic position. The α-hydroxy acid products can be converted into γ-lactones using a variety of lactonization conditions.     

Transition metal-catalyzed formation of CF3-substituted α,β-unsaturated alkene and the synthesis of α-trifluoromethyl substituted β-amino ester

A new transition metal-catalyzed formation of CF₃-substituted α,β-unsaturated alkenes through the ylide intermediate from the reaction between methyl 3,3,3-trifluoro-2-diazopropionate 1 and aryl aldehydes has been developed. Further transformation of the alkene affords the α-trifluoromethyl substituted β-amino ester, a valuable intermediate in the synthesis of fluorine-containing amino acids with potential biological application.     

Rhodium-catalyzed intramolecular formation of N-sulfamoyl 2,3-aziridino-γ-lactones and their use for the enantiospecific synthesis of α,β-diamino acid derivatives

4-Hydroxymethylbutenolide 4 was transformed into its sulfamoyl derivative 5, which upon treatment with iodosobenzene diacetate and magnesium oxide in the presence of a rhodium catalyst afforded the product of intramolecular aziridination 6. Reaction of 6 with primary or secondary amines in DMA led to regioselective opening of the aziridine ring at C2 to give the corresponding bicyclic derivatives 7a-7g in good to excellent yields. Methanolysis of the lactone ring of the N-benzyl-N-methyl derivative 7c followed by protection of the resulting secondary hydroxy group and treatment of the product with Boc anhydride provided the activated cyclic sulfamates 13 and 14. The latter then reacted with a second nucleophile (azide or thiophenol) to give the corresponding difunctionalized α,β-diamino methyl esters 15-18, 20.     

Metal-mediated allylation of mucohalic acids: facile formation of γ-allylic α,β-unsaturated γ-butyrolactones

Mucohalic acids {mucochloric acid (1, 3,4-dichloro-5-hydroxy-5H-furan-2-one and mucobromic acid (2, 3,4-dibromo-5-hydroxy-5H-furan-2-one)} were employed as aldehydes in the indium- and tin-mediated Barbier-type allylation reactions and afforded γ-allylic α,β-unsaturated γ-butyrolactones in good to excellent yield.     

Development of methods for the synthesis of libraries of substituted maleimides and α,β-unsaturated-γ-butyrolactams

Synthetic methods for the preparation of maleimide and α,β-unsaturated-γ-butyrolactam compound collections are described. These routes take advantage of Pd cross-coupling and conjugate addition/elimination reactions to permit the facile production of bisaryl-maleimides, anilinoaryl-maleimides, and bisanilino-maleimides while allowing control over the synthesis of symmetrical or nonsymmetrical derivatives. Similarly, the chemistry developed allows for the generation of bisaryl substituted α,β-unsaturated-γ-butyrolactams. The scope and limitations of the approaches are presented.     

Synthesis of (2,2,2-trifluoroethyl) substituted pyridazin-3(2H)-ones and 1,5-dihydropyrrol-2-ones from α,β-unsaturated γ-lactones and hydrazines

This paper presents the transformation of α,β-unsaturated γ-lactones into 2,2,2-trifluoroethyl substituted pyridazin-3(2H)-ones and 1,5-dihydropyrrol-2-ones starting from various hydrazines. The influence of the γ-lactone substitution (sulfanyl versus sulfonyl moiety) and the nature of the hydrazines (unsubstituted, alkyl- or aryl-substituted) on the outcome of the reaction were studied. All new heterocycles were characterized using 1D NMR, IR, MS and their data was compared with those of two reported X-ray diffraction structures. The two possible competitive pathways leading to pyridazin-3(2H)-ones and/or 1,5-dihydropyrrol-2-ones are discussed. Abinitio DFT calculations were also performed in order to rationalize several experimental results.     

Enantioselective α- and γ-alkylation of α,β-unsaturated aldehydes using dienamine activation

The enantioselective alkylation of α,β-unsaturated aldehydes with stabilized carbocations as electrophiles via the activation as dienamine intermediates is described. This unique application of dienamine catalysis allows for the first enantioselective γ-alkylation of linear α,β-unsubstituted enals.     

Chemoenzymatic synthesis of chiral substituted acrylate and acrylonitrile precursors for the synthesis of 3-deoxy-2-ulosonic acids and α-methylene-γ-lactones

Substituted acrylonitrile and ethyl acrylate bearing a masked α-hydroxyaldehyde were easily synthesised by a Barbier type reaction between the monoacetal of glyoxal and bromomethyl acrylonitrile or ethyl bromomethyl acrylate. We prepared these interesting synthons in an enantiomerically pure form by enzymatic resolution with Candida rugosa lipase, or by microbial reduction of the corresponding ketones using Aspergillus niger and Lactobacillus kefir.     

Synthesis of α,β-unsaturated γ-lactones via photooxygenation of 2,3-dihydrofurans followed by ferrous ion-catalyzed gem-dehydration

Several alkyl and aryl substituted 2,3-dihydrofurans 1a-1e were synthesized and their reactions with singlet oxygen were investigated. Photooxygenation of 1a-1e in carbon tetrachloride at ambient temperature exclusively yields allylic hydroperoxides 4a-4e. Treatment of these hydroperoxides with aqueous ferrous sulfate solution affords the corresponding α,β-unsaturated γ-lactones 6a-6e with high yields. This work provides an efficient route to the preparation of butenolide moiety, an important functionality in the structures of many natural products that exhibit biological properties.     

Asymmetric synthesis of γ-lactones through reaction of sulfoxonium ylides,aldehydes, and ketenes

A method for the enantioselective synthesis of γ-lactones through the reaction of enantioenriched sulfoxonium ylides, aldehydes, and ketenes was developed. Enantioenriched (98% ee) aminosulfoxonium ylide was subjected to reaction with a variety of aldehydes (both aromatic and aliphatic) and disubstituted ketenes, leading to the formation of α,β-substituted γ-lactones in moderate to very good diastereoselectivity (dr up to 95:5) and with enantiomeric excesses of up to 79% ee. Best levels of enantioselectivity were observed in the reactions of enantioenriched aminosulfoxonium ylide with isobutyraldehyde and various alkylarylketenes.     

Synthesis and reactions of sulfur-substituted α,β-unsaturated δ- and γ-lactones

A new synthetic method for the preparation of sulfur-substituted α,β-unsaturated δ- and γ-lactones has been developed by reaction of the allylic bromides of 5,6-dihydro-2-pyridinones with NaOH in refluxing MeOH or t-BuOH. The substituents at C5 and C6 of these substrates are very important for the success of this reaction. Some synthetic transformations of the α,β-unsaturated δ-lactones have also been carried out.     

Direct formation of α,β-unsaturated dithioacetals from diarylpropynols

The acid-catalysed condensation of a series of 1,1-diarylprop-2-yn-1-ols with 2-thionaphthol unexpectedly gave 3,3-diaryl-1,1-bis(2-naphthylthio)prop-2-enes in good yields via a Meyer-Schuster-type rearrangement.     

Selective carbometallation of α,β-unsaturated carbonyl compounds and substituted oxacyclopropanes with zirconium-diene complexes

The reactions of zirconium-dience complexes, ZrCp₂(s-cis-diene), with bifunctional electrophiles, i.e. α,β-unsaturated ketones, unsaturated esters and substituted oxacyclopropanes, were investigated. Reaction of ZrCp₂(s-cis-isoprene) with an equivalent of 3-buten-2-one or alkyl acrylates, selectively gives 1,2-addition products. CC bond formation occured at the C(1) atom of the isoprene moiety whereas 1,3-pentadiene-, 2-methyl-1,3-pentadiene- and 2,4-dimethyl-1,3-pentadiene complexes induced the regioselective 1,2-addition at the C(4) position of the diene moiety. Phenyloxacyclopropane and 2-methyl-3-phenyl-oxacyclopropane also react with ZrCp₂(isoprene) leading to CC bond formation from the C(1) atom of isoprene to the oxirane carbon bearing the phenyl group. The corresponding reactions of 2-methyl-2-butene-1,4-diylmagnesium with α,β-unsaturated carbonyl compounds were also studied and found to give quite different products.     

Steric effects in the catalytic amination of γ-, δ-, and ε-glycols

The amination of butane-1,4-diol, isomeric dipropylene glycols, and cyclohexane-1,4-diyldimethanol in the presence of nickel/copper/chromium catalysts has been studied. The effect of the initial glycol structure on the reaction selectivity has been estimated.