Silica Chloride–Catalyzed Synthesis of Thiiranes from Oxiranes Under Solvent-Free Conditions

A mild, simple, and efficient method for the synthesis of thiiranes from epoxides using a catalytic amount of silica chloride under solvent-free conditions has been developed. Experimental simplicity, simple work-up procedure, and solvent-free reaction conditions are important features of the present protocol.     

Ammonium Chloride–Catalyzed One-Pot Synthesis of 4(3H)-Quinazolinones Under Solvent-Free Conditions

Ammonium chloride, which is a very inexpensive and readily available reagent, can efficiently catalyze three-component, one-pot condensation reactions of 2-amino-benzoic acid esters, ortho esters, and aromatic amines to afford the corresponding 4(3H)-quinazolinones in good to excellent yields under solvent-free conditions.     

Stannous Chloride–Promoted Synthesis of S-Allyl-N-aryl Dithiocarbamates under Solvent-Free Conditions

Abstract

A highly efficient method of synthesis of S-allyl-N-aryl dithiocarbamates using SnCl₂ as a catalyst under solvent-free conditions is described. The mild reaction conditions, high yields, and shorter reaction period illustrate the good synthetic utility of this method.     

Convenient In-Flow Preparation of Cr(II) Chloride for Nozaki–Hiyama–Kishi Reaction

A flow preparation of chromous chloride has been introduced as a viable alternative to the batch protocol. Activity of the prepared reagent has been demonstrated in the traditional Nozaki–Hiyama–Kishi reaction.     

Cobalt(II) Chloride Complex Formation in Acetamide–Calcium Nitrate Tetrahydrate Melts

The absorption spectra of Co(II) chloride complexes, containing variable concentrations of chloride ligand, in a molten mixture of 80 mol% acetamide–20 mol% calcium nitrate tetrahydrate, were studied at 313, 333, 353, and 363 K, in the wavelength range 400-800 nm. The melt contains three possible ligands (CH₃CONH₂, H₂O, and NO₃ ^-) for competition with added chloride ligand. Addition of chloride caused a shift of the absorption maximum of octahedral cobalt(II) nitrate towards lower energies and pronounced changes in the shape of the initial spectrum of cobalt(II) nitrate. The effect of temperature changes on the molar absorption coefficient of the Co(II) species was dependent on the chloride concentration and was attributed to the structural changes occurring in the cobalt(II) species. The STAR and STAR FA programs were applied to identify the complex ionic species and to calculate the stability constants of Co(II) complexes formed in this solvent. The results indicate the highest probability of formation of the following complex species: Co(NO₃)₄ ^2-, Co(NO₃)₂Cl₂ ^2-, and CoCl₄ ^2-. Stability constants of each complex were presented for the equilibria occurring at 313, 333, 353, and 363 K. Distribution of the Co(II) species was also calculated over the ranges of chloride concentration and temperature investigated.     

Convenient Preparation of 2-Deoxy-3,5-di-O-p-toluoyl-α-D-erythro-pentofuranosyl Chloride

By using acetyl chloride as HCl generator, the procedure for the Hoffer preparation of the α-chloro sugar 4a was significantly improved. The α-configuration of the chloro atom was confirmed by using NOE measurement. Sequential transformation of 4a to the β-anomer and to the furfuryl derivative 6 was studied.     

Ammonium Chloride–Catalyzed One-Pot Synthesis of Tetrahydrobenzo[α]xanthen-11-one Derivatives Under Solvent-Free Conditions

A one-pot, multicomponent reaction of aldehydes, dimedone, and β-naphthols is described for the preparation of 12-aryl- or 12-alkyl-8,9,10,12-tetrahydrobenzo[α]xanthen-11-one derivatives using ammonium chloride as a mild, inexpensive, and environmentally benign catalyst under solvent-free conditions. Different types of aldehyde and β-naphthol derivatives are used in the reaction, and in all cases the products were synthesized successfully.

Preparation of l-Nα-Fmoc-4-[di-(tert-butyl)phosphonomethyl]phenylalanine from l-tyrosine

The unnatural amino acid analogue, 4-(phosphonomethyl)phenylalanine (Pmp, 2), has proven to be a valuable tool for studying protein-tyrosine kinase dependent signal transduction, where it is most often incorporated into peptides or peptide mimetics as a phosphatase-stable phosphotyrosyl mimetic. Although Pmp has been prepared previously bearing a number of protection strategies, the N^α-Fmoc 4-[di-(tert-butyl)phosphonomethyl] phenylalanine form [(N^α-Fmoc-l-Pmp(^tBu₂)-OH, 3] is particularly attractive since it can be cleanly introduced into peptides using standard Fmoc protocols. Synthesis of 3 was first reported as its (d/l)-racemate, and subsequently as its l-3 enantiomer, with the latter synthesis having relied on induction of chirality using a camphor sultam auxillary. Reported herein is an alternate enantioselective synthesis of l-3 in high enantiomeric purity by procedures which derive the stereochemistry of the final product directly from the starting amino acid, without the need for chiral induction. A key feature of the route is the racemization-free nucleophilic substitution of lithium di-tert-butyl phosphite onto protected 4-bromomethylphenylalanine (17).     

Chlorodimethylsulfonium Chloride–Mediated Formation of Phenyl-α-chloroazoalkanes

Phenylhydrazones (1) are efficiently converted into phenyl-α-chloroazoalkanes (2) upon treatment with chlorodimethylsulfonium chloride. Pendent olefins, silyl ethers, and the phenyl ring of the hydrazone are stable to these reaction conditions.     

A Convenient One-Step Synthesis of 5-(α-alkanonyl) and 5-(α-Cyclanonyl)-4-Pentanolides

The thermolysis of t-butyl perpent-4-enoate in ketones leads to the formation of 5-(α-alkanonyl) and 5-(α-cyclanonyl)-4-pentanolides with fairly good yields.     

The Preparation of New C(α)-Dianions

For more than a decade, Hauser et. al. carried out rather extensive investigations on the preparation and reactions of the multiple anions of β -diketones and related materials. Once the conditions for the preparation of a particular multiple anion seemed established, three reactions were usually attempted with the new multiple anion: alkylations with reagents such as benzyl chloride², Aldol-type condensations with aldehydes or ketones³ such as benzaldehyde and benzophenone, and Claisen-type condensations with esters such as methyl benzoate⁴. Other electrophilic reagents, such as nitriles⁵ and isocyanates⁶, were also condensed with certain of these multiple anions in selective situations; however, the alkylations, acylations, and carbonyl additions received the greatest amount of attention⁷. In some cases only one of the three types of reactions (Aldol) worked well⁸; however this did not mean that conditions could not be found for the other two reaction types. In addition, the synthetic potential of these multiple anion reactions was quite extensive (Scheme 1).     

Preparation of (±)-α-alkylated amino acid derivatives via imidazoles

Photooxidatlon of N-methoxy-2,4-disubstituted imidazoles, readily available by way of a three component cyclization followed by O-alkylation, leads to stable acyl Imines which react with various organometallics to afford α,α-disubstituted amino acid bis-amides in good yields.     

Synthesis of an analog of ( )-goniopypyrone from 3- O- benzyl-1,2- O-isopropylidene-5- C-phenyl-α-D-gluco-pentofuranose

8,9-Dimethoxy-7-epi-goniopypyrone, an analog of ( )-go-niopypyrone, was synthesized from 3-O-benzyl-1, 2-O-iso-propylidene-5-C-phenyl-α-D-gluco-pentofuranose (3).     

Indium(III) Triflate–Mediated One-Step Preparation of Glycosyl Halides from Free Sugars

In(OTf)₃ has been found to be an efficient catalyst for the direct conversion of reducing sugars to their respective acylated glycosyl halides in good yields under mild conditions. The glycosyl halides so obtained can be converted to alkyl glycosides in the same pot by reacting them with the respective alcohols in good yield.     

Synthesis of ( )-5α-Hydroxy-β-selinene and (-)-5β-Hydroxy-β-selinene

Eudesmanederivativeshavebeendrawingconsiderableattentionduetotheirwidespectrumofbiologicalproperties,particularlyantifeedant,cellgroWthinhibitoryandplantgroWthregulatingactivitiesl'2.Recently,twoepimericeudesmanederivatives( )-5a-hydroxy-6-selinene1and(-)-56-hydroxy-6-selinene2wereisolated3fromtheaerialpartsofCSubtraPicaFMell.,andtheirstructuresweredeterminedbyspectroscopicmethods.Herein,wereportafacilesynthesisofbothtwodiastereomers1and2from( )-dihydrocarvone3infivesteps,usingtheregioselect…     

Polyfluorophenylaminosilane–Titanium (IV) Chloride Adducts

Si(NHC₆H_5-nF_n)₄.xTiCl₄ [n = 2–5; x = 3,4] are obtained from the disproportionation reactions between (CF₃CH₂O)₃SiNHC₆H_5-nF_n (n = 2–5) and TiCl₄ in petroleum ether (40–60°C) at 0°–10°C. These complexes are characterized by elemental analyses and IR, ¹H, and ¹⁹F NMR spectroscopy. Unlike the reported⁵ complex Si(NHC₆H₄F-o)₄.3TiCl₄, these are non-ionic in nature. All complexes give double adducts with CH₃NO₂ and CH₃CN within 24 h.     

Polystyrene and Silica Gel–Supported,AlCl3-Catalyzed Preparation of Diaryl Sulfoxides from Arenes and Thionyl Chloride

A simple, chemoselective, and efficient method has been developed for direct conversion of arenes to symmetrical diaryl sulfoxides using thionyl chloride in the presence of a catalytic amount of cross-linked polystyrene-supported aluminium chloride (Ps-AlCl₃) and silica gel–supported aluminium chloride (SiO₂-AlCl₃). These solid acid catalysts are stable and can be easily recovered and reused without appreciable change in their efficiency.     

Preparation and Characterization of 61,6n-DI-O-(α-D-Galactopyranosyl)Cyclomaltooctaoses

ABSTRACT

Four positional isomers of 6¹,6ⁿ-di-O-(D-galactopyranosyl)cyclomaltooctaoses (cG₈s, γ-cyclodextrins) (n = 2?5) were chemically synthesized using the trichloroacetimidate method. The desired compounds having two α-(1→6)-linkages were isolated from a mixture of configurational isomers by HPLC, and their structures were confirmed by ¹³C NMR spectroscopy and FAB-high resolution mass spectra (HRMS). The elution behavior of their four positional isomers on an ODS column by HPLC is discussed.     

A short synthesis of (S)-α-(diphenylmethyl)alkyl amines from amino acids

A range of (S)-α-(diphenylmethyl)alkyl amines were prepared from the corresponding (S)-α-amino acid ester hydrochlorides. These amines were derived by direct hydrogenation of their precursor oxazolidinones.     

A New (–)-5′,6-dimethoxyisolariciresinol-(3″,4″-dimethoxy)-3α-O-β-D-glucopyranoside from the bark of Aglaia eximia (Meliaceae)

New (–)-5′,6-dimethoxyisolariciresinol-(3″,4″-dimethoxy)-3α-O-β-d-glucopyranoside compound was isolated from the methanol extract of the bark of Aglaia eximia (Meliaceae). The chemical structure of the new compound were elucidated on the basis of spectroscopic data including, UV, IR, HR-ESI-TOFMS, 1D-NMR, 2D-NMR and comparison with those related compounds previously reported.