Stereoselective synthesis of β-(hydroxymethylaryl/alkyl)-α-methylene-γ-butyrolactones

Zinc or a chromium(II) source with 3-(bromomethyl)furan-2(5H)-one (3) and an aldehyde gives β-(hydroxymethylaryl/alkyl)-α-methylene-γ-butyrolactones 5 in good yields and high diastereoselectivities. The methodology is demonstrated in concise syntheses of (±)-hydroxymatairesinol (8) and (±)-methylenolactocin (10) by subsequent arylboronate conjugate addition and translactonization, respectively.     

Stereospecific interconversion of cis- and trans-γ,δ-epoxy α,β-unsaturated ester systems

The unprecedented, stereospecific interconversion of cis- and trans-γ,δ-epoxy α,β-unsaturated ester systems has been realized, which involves the palladium-catalyzed stereospecific alkoxy or hydroxy substitution reaction with double inversion of configuration at the γ-position as the key step. The new methodology is not only applicable to various disubstituted and trisubstituted epoxy unsaturated esters, but also these interconversions proceed with an extremely high degree of stereoselectivity and efficiency.     

Synthesis of cis-3,4-diaryl α-methylene-γ-butyrolactams via sonochemical Barbier-type reaction

A series of cis-3,4-diaryl α-methylene-γ-butyrolactams were synthesized by the addition reaction of 3-phenylallyl bromide with N-tosyl aldimine via sonochemical Barbier-type reaction condition and then followed by the in situ intramolecular amidation. The cis-3,4-diaryl α-methylene-γ-butyrolactam was obtained as the sole regio- and stereoisomeric product when N-tosyl aldimine was used as the substrate whereas the monoaryl α-methylene-γ-butyrolactam was also generated when N-phenyl aldimine was used.     

Asymmetric Synthesis of β, γ-β-Hydroxyl-γ-butyrolactones

Chiral β-hydroxyl-γ-butyrolactones have attracted substantial interest in recent years due to their presence inmany strongly active natural products having antitumor, fungicidal, anti-inflammatory activity, and their use as important precursors in natural product synthesis. [1] In the course of the total synthesis of the natural product Tuxpano lide ,[2] we found a concise and efficient strategy on the stereocontrolled synthesis of β-hydroxyl-γ-butyrolactonederivatives from cheap and achiral starting material.     

Efficient synthesis of 3-hydroxymethylated cis- and trans-cyclobutane β-amino acids using an intramolecular photocycloaddition strategy

Uracil bearing a tethered allyl alcohol appendage at N1 undergoes a [2+2] photocycloaddition reaction to provide a single tricyclic adduct in high yield. This compound is transformed in one step into a cis-cyclobutane β-amino acid bearing a 3-hydroxymethyl group. Through appropriate functionalization and epimerization, the trans isomer is obtained therefrom in only three further steps.     

Synthesis of cis- and trans-(±)-3-mercaptoproline and pipecolic acid derivatives via thio-Michael addition

The reactivity of 2,3-dehydroproline and 2,3-dehydropipecolic acid methyl ester derivatives with S-nucleophiles in the thio-Michael addition reaction has been explored. The addition of triphenylmethanethiol and subsequent trityl cleavage led to the corresponding cis- and trans-(±)-3-mercaptoproline and pipecolic acid derivatives in good yields.     

Silver-catalyzed spirolactonization: first synthesis of spiroisoindole-γ-methylene-γ-butyrolactones

γ-Acetylenic carboxylic acids are cyclized to spirolactones under mild conditions, in the presence of Ag₂CO₃ catalyst. The corresponding spiro-5-alkylidene-γ-butyrolactones were isolated in high yields, and this process constitutes an easy and efficient route to analogous structures of natural products of biological interest.     

Intramolecular allylboration of γ-(ω-formylalkoxy)allylboronates for syntheses of trans- or cis-2-(ethenyl)tetrahydropyran-3-ol and 2-(ethenyl)oxepan-3-ol

3-Alkoxy-1-alkynes 4 were hydroborated with pinacolborane (HBpin) to give 3-alkoxy-1-alkenylboronates 5. The latter gave (E)-3-alkoxyallylboronates (8: (E)-(MeO)₂CHCH₂(CH₂)_nCH₂OCHCHCH₂Bpin, n=1-3) when they were subjected to iridium-catalyzed isomerization of the double bond. The corresponding (Z)-isomers 10 were synthesized by nickel-catalyzed isomerization of 5. Both allylboronates underwent intramolecular allylboration leading to the formation of trans-2-(ethenyl)tetrahydropyran-3-ol or 2-(ethenyl)oxepan-3-ol from 8 and the corresponding cis-isomers from 10 in the presence of Yb(OTf)₃ (20 mol%) in aqueous acetonitrile at 90°C.     

Stereoselective syntheses of γ-alkyl (aryl)-α,β-dihydroxy-γ-butyrolactones and naturally occurring lipid guggultetrol

γ-Oxo-butyramides derived from tartaric acid serve as excellent precursors for the synthesis of γ-alkyl (aryl)-α,β-dihydroxy-γ-butyrolactones and for the synthesis of tetrols containing three contiguous stereogenic centres. The methodology presented here is general for the synthesis of γ-alkyl (aryl)-α,β-dihydroxy-γ-butyrolactones. Utility of the chiral building block was demonstrated by the synthesis of naturally occurring lipid guggultetrol.     

Syntheses and structures of tetraphenylantimony γ-phenyl-and γ-thiobutylacetylacetonates

Tetraphenylantimony γ-phenylacetylacetonate (I) and tetraphenylstibium γ-thiobutylacetylacetonate (II) are synthesized by the reaction of pentaphenylantimony with γ-phenylacetylacetone or γ-thiobutylacetylacetone in toluene. According to the X-ray diffraction data, the antimony atoms in complexes I and II have a distorted octahedral coordination. In complex I, the Sb-C bond lengths are 2.155(2)–2.170(1) Å, and the Sb-O(1), Sb-O(2) and O(1)-C(2), O(2)-C(4) in the heterocycle are 2.215(1), 2.227(1) and 1.282(2), 1.277(2) Å, respectively. In complex II, the bond lengths are the following: Sb-C 2.147(3)–2.161(3), Sb-O(1, 2) 2.281(2), 2.215(2), and O-C 1.267(3)–1.278(3) Å.     

Macrocyclic cis- and trans-bis(α-amino acids) and their intraannular Cu(II) complexes. Conformational in-out dichotomy and crystal packing

Macrocyclic bis(α-amino acids) cis- and trans-2a-b were prepared from the selectively protected tris(hydroxymethyl)aminomethane 3. The X-ray structures of the free bis(amino acids) and/or of the corresponding Cu(II) complexes have been determined allowing an unambiguous configurational assessment. At the same time, conformational in-out dichotomy of the functional groups has been demonstrated in the bis(amino acids) as well as in their Cu(II) complexes.     

Asymmetric synthesis of α-alkyl-α-hydroxy-γ-butyrolactones

A new enantioselective approach to α-alkyl-α-hydroxy-γ-butyrolactones employing (1R,2S)-ephedrine-derived chiral allyl morpholinones as starting materials is described.     

The hydrocyanation route to β- and γ-amino acids. A synthesis of α-methylene-β-alanine

Hydrocyanation of several phthalimidoalkynes proceeds with good regioselection yielding products which were easily converted into unsaturated and saturated β- and γ-amino acids.     

Synthesis of cis-3-hydroxypipecolic acid via SmI2-mediated cyclization of aldehydo β-aminovinyl sulfoxides

Stereoselective synthesis of cis-3-hydroxypipecolic acid was achieved via chirality transfer in the SmI₂-mediated cyclization reactions of aldehydo β-aminovinyl sulfoxides.     

Syntheses and Structure-Odor Relationship of Some γ-Lactones

A lot of norbornene derivatives and lactones are widely used as fragrant components in food or cosmetics. We expected that a series of new compounds with better odor character could be obtained when these two skeleton structures were combined. Thus, a series of endoand exo-5,5-disubstituted-3-oxo-4-oxatricyclo[5,2,1,0~(2,6)]dec-8-enes(Ⅰ) were synthesized.     

Highly stereoselective synthesis of trans-4-trifluoromethylsulfonyl-2,3-dihydrofurans from arsonium ylides and (E)-α-trifluoromethylsulfonyl-α,β-unsaturated ketones

The reactions of arsonium bromides with (E)-α-trifluoromethylsulfonyl-α,β-unsaturated ketones in the presence of Cs₂CO₃ or K₂CO₃ proceeded smoothly under refluxing condition in dichloromethane (DCM) to give the corresponding trifluoromethylated trans-2,3-dihydrofurans in good to excellent yields with high stereoselectivity.     

α- and β-Mercaptoalkanoic Acids: Versatile Synthons in the Syntheses of Thiasteroid Analogues and Selenathiadiazoles

This review describes the reactions of α/β-mercaptoalkanoic acids as building blocks for the synthesis of heterosteroids, polyfunctional heterocycles with pharmacological interest. Annelated heterocycles have been prepared by the cyclocondensation reaction of α- and β-mercaptoalkanoic acids with carbonyl compounds. This reaction takes place by nucleophilic addition, followed by cyclization with elimination of water. The main objective of this survey is to provide a comprehensive account of this reaction type in building various heterocycles, and examining their potential in developing better chemotherapeutic agents.     

Study of the mechanism of base induced dehydrobromination of trans-β-bromostyrene

Observation that rates of dehydrobromination of trans-β-bromostyrene (1) and the Hofmann degradation of tetrabutyl ammonium cation depend on strength of base in different ways and that treatment of 1 with base results in fast abstraction of the β-proton imply the possibility that the dehydrobromination of 1 could proceed via α-elimination and Ph migration. In order to clarify this question, β-¹³C-labeled 1 was obtained and subjected to PTC dehydrobromination which proceeds without migration of Ph. The obtained results are consistent with an irreversible E1cB mechanism.