Microwave‐Promoted Beller's Synthesis of Substituted Phthalates

A rapid and efficient synthesis of substituted phthalates via microwave‐promoted Beller's reaction of aldehydes, amides, and dimethyl acetylenedicarboxylate is described. This one‐pot, multicomponent reaction was performed under acetic anhydride–free and solvent‐free conditions.     

Controlled Synthesis of meso‐Veratrylporphyrins under Acid‐Catalyzed Scrambling Conditions

5,15‐Bis(veratryl)porphyrin (1), 5,10,15‐tris(veratryl)porphyrin (2), and 5,10,15,20‐tetrakis(veratryl)porphyrin (3), C₃₆H₃₀N₄O₄, C₄₄H₃₈N₄O_6, and C₅₂H₄₆N₄O₈ were synthesized by an acid‐catalyzed, one‐pot reaction of meso‐dipyrromethane, 3,4‐di‐OCH₃‐benzaldehyde (veratraldehyde), and trifluoroacetic acid (TFA). These three different products were obtained as a result of scrambling reactions. The molecular structures have been characterized by elemental analysis, ESI mass spectra, 1D and 2D NMR techniques (¹H and ¹³C), and UV‐visible spectroscopy.     

A Mild and Efficient Synthesis of bis‐Indolylmethanes Catalyzed by Sulfamic Acid

A mild and efficient electrophilic substitution reaction of indoles with various aldehydes under catalysis of sulfamic acid afforded biologically important bis‐indolymethanes in good yields.     

Synthesis of (−)‐Isofagomine

Abstract

1,3‐Dipolar cycloaddition of N‐benzyl nitrone 2 to D‐threo δ‐lactone 15 proceeded with excellent stereoselectivity to provide only one adduct 16. Cycloadduct 16 was subsequently subjected to a sequence of reactions involving rearrangement to γ‐lactone, glycolic cleavage/reduction, protection of the terminal hydroxymethyl group, reduction of the lactone, desilylation/mesylation, and hydrogenolysis of the N‐O bond providing (?)‐isofagomine and its N‐substituted derivatives. The biologic activity of N‐substituted (?)‐isofagomines toward commercially available α‐ and β‐glucosidases, α‐D‐mannosidase, α‐L‐fucosidase, β‐D‐glucuronidase, and β‐D‐galactosidase was tested.     

Alternative,High‐Yield Synthesis of (E)‐4‐Oxonon‐2‐enoic Acid from 2‐Methoxyfuran

Alkylation of 2‐methoxyfuran, followed by in situ TPP‐sensitized photooxygenation of 2‐methoxy‐5‐pentylfuran in the presence of Me₂S, gave methyl (Z)‐4‐oxonon‐2‐enoate. Hydrolysis of methyl (Z)‐4‐oxonon‐2‐enoate afforded (E)‐4‐oxonon‐2‐enoic acid in three steps and in 79% overall yield.     

Microwave‐Assisted Synthesis of Azocalixarenes

Five new water‐soluble and two water‐insoluble azocalixarenes have been synthesized by coupling reaction of different substituted anilines and terta hydroxylcalix[4]arene. These dyes have been characterized by ¹H NMR, ¹³C NMR, FAB mass, and elemental analysis.     

Microwave‐Assisted Beckmann Rearrangement: Convenient Synthesis of 1,3‐Diaza‐bicyclo[3.2.2]nonane

Small heterocyclic amines such as 1,3‐diaza‐bicyclo[3.2.2]nonane are known to be key components of biologically active molecules. A convenient synthesis of this compound utilizing a key Beckmann rearrangement of (Z)‐1‐aza‐bicyclo[2.2.2]octan‐3‐one oxime (6) with conc. H₂SO₄ under microwave irradiation was achieved. The desired compound (1) was obtained in 20% yield overall.     

Perchloric Acid Supported on Silica Catalyzed Efficient Synthesis of 1,5‐Benzodiazepines

Perchloric acid adsorbed on silica gel efficiently catalyzed the condensation of o‐phenylenediamines (OPDA) with cyclic and acyclic ketones at ambient temperature to afford 1,5‐benzodiazepines in good yields under solvent‐free conditions.     

Microwave‐Assisted NiCl2 Promoted Acylation of Alcohols

Abstract

A microwave oven acylation of alcohols by carboxylic acid anhydrides has been developed. NiCl₂ has been proven an efficient catalyst for the acylation of primary, secondary, and tertiary alcohols and phenols under microwave conditions.     

Acid‐Promoted Ring Opening of α‐Hydroxyl Cyclobutanones: A Novel and Facile One‐Pot Synthesis of Nitrile Derivatives

A facile one‐pot synthesis of nitriles via a ring‐opening reaction of cyclobutanone adducts with hydroxylamine hydrochloride was developed.     

An Efficient One‐Pot Synthesis of 3,4‐Dihydropyrimidin‐2‐ones Catalyzed by Methanesulfonic Acid

Abstract

An efficient synthesis of 3,4‐dihydropyrimidin‐2‐ones (DHPMs) from the aldehydes, β‐ketoesters, and urea in ethanol using methanesulfonic acid (CH₃SO₃H) as the catalyst is described. Compared with the classical Biginelli reaction conditions, this method has the advantage of excellent yields and short reaction time.     

Synthesis of (+)- and (−)-Phaselic Acid

The syntheses of both enantiomers of phaselic acid (2-O-caffeoylmalate) are described. The previously unreported acetate-protected caffeic acid anhydride was used with appropriately protected malic acid derivatives as coupling partners to provide fully protected phaselic acid. Sequential unmasking of the protecting groups afforded phaselic acid in an acceptable overall yield.

Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file.     

A Regioselective Synthesis of Tetrahydrobenzodiazepin‐5‐ones via the Schmidt Rearrangement of Quinolones

Abstract

The regioselective synthesis of 2,3,4,5‐tetrahydro‐1H‐1,4‐benzodiazepin‐5‐ones by the Schmidt rearrangement of 1,2,3,4‐tetrahydro‐4‐quinolones with oxygen substituents at C‐8 is described.     

Comparison of Base‐Promoted and Self‐Catalyzed Conditions in the Synthesis of Isocyanates from Amines Using Triphosgene

Comparison of base‐promoted and self‐catalyzed conditions for the synthesis of isocyanates from amines and triphosgene shows no advantage in using an amine base in the majority of cases. The workup and isolation of the product is simplified under base‐free conditions. Yields of between 50 and 90% after distillation were common. Only acid‐sensitive substrates need a base catalyst.     

Lithium Tetrafluoborate Catalyzed Ferrier Rearrangement — Facile Synthesis of Alkyl 2,3-Unsaturated Glycopyranosides

Treatment of tri-O acetyl-D-galactal 1 and tri-O-acetyl-D-glucal 2 with diverse alcohols in the presence of LiBF₄ in CH₃CN, furnished alkyl 2,3-unsaturated glycopyranosides 3-18 (50-86%).     

Microwave‐Promoted Ullmann Condensation of 2‐Aminopyridines with 2‐Chlorobenzoic Acids

A new efficient synthetic method of microwave‐promoted Ullmann condensation of 2‐aminopyridines with 2‐chlorobenzoic acids to yield various substituted 11H‐pyrido[2,1‐b]quinazolin‐11‐ones in dry media is presented. Results were compared with those obtained following the classical heating.     

A Protecting-Group-Free Synthesis of (−)-Salvinorin A

A concise enantioselective total synthesis of the neoclerodane diterpene (−)-salvinorin A is reported. The stereogenic center at C-12 was installed by catalytic asymmetric propargylation with excellent enantioselectivity, and the remaining six stereogenic centers were set up highly diastereoselectively under substrate control. As for our previous synthesis of racemic salvinorin A, two intramolecular Diels-Alder reactions were applied to generate the tricyclic core. A chemoselective Mitsunobu inversion of a syn 1,2-diol allowed for further streamlining of the original reaction sequence by two steps. Overall, (−)-salvinorin A was synthesized in only 16 steps starting from 3-furaldehyde with 1.4 % total yield. Furthermore, an alternative intramolecular Diels-Alder strategy employing a 2-bromo-1,3-diene moiety was investigated.     

Microwave‐Assisted One‐Pot Synthesis of 1,2,3,4‐Tetrahydrocarbazoles

A series of 1,2,3,4‐tetrahydrocarbazoles 3a–m were synthesized by the reaction of substituted 2‐bromocyclohexanones 2a–c with appropriate anilines 1a–i under microwave irradiation without any other catalysts.     

A Stereoselective Synthesis of (−)-Endo-Brevicomin

A stereoselective synthesis of (1S,5R,7R) (-)-endo-brevicomin by employing Sharpless kinetic resolution method has been described.     

Total Synthesis of (−)-Glaucocalyxin A

A practically useful method for the formation of the highly oxygenated bicyclo[3.2.1]octane ring system through Mn(OAc)₃-mediated radical cyclization of alkynyl ketones was developed, which opens up a new avenue for the total synthesis of a number of highly oxidized diterpenoids. Application of this method enabled the first total synthesis of (−)-glaucocalyxin A. Other salient features of the synthesis include a highly enantioselective conjugate addition/acylation cascade reaction, a Yamamoto aldol reaction, and an intramolecular Diels–Alder reaction to assemble the A/B ring system.