Regioselective Synthesis of Coumarin‐Annulated Polyheterocycles by [3,3] Sigmatropic Rearrangement

Several coumarin‐annulated polyheterocycles have been regioselectively synthesized in 82–90% yield by anhydrous AlCl₃‐catalyzed charge‐accelerated Claisen rearrangement of 4‐aryloxymethyl [3,2‐c] pyrano benzopyran‐5‐ones in dichloromethane at rt for 0.5 h.     

Efficient One‐Step Synthesis of a Key Intermediate for the Synthesis of Azole Antifungals Using the Mitsunobu Protocol

A simple and single‐step process for coupling (2R,1S)‐1‐[2‐(2,4‐difluorophenyl)‐2‐oxiranyl]ethanol and various 1,2,4‐triazolones utilizing the Mitsunobu protocol is described. The product so formed is a key intermediate in the synthesis of azole antifungals with potent and broad‐spectrum activity against yeast and filamentous fungi.     

Catalytic Asymmetric [2, 3]－Sigmatropic Rearrangement of Sulfur Ylides Generated from Carbenoids and Allenic 2－Methylphenyl Sulfide

The first investigation on catalytic asymmetric [2,3]-sigmatropic rearrangement of sulfur ylides generated from carbenoids and allenic phenyl sulfide was carried out. Up to 55% ee value was obtained.     

Sequential [3,3]Sigmatropic Rearrangement: Regioselective Synthesis of Dimedone‐Annulated Heterocycles

The [3,3]sigmatropic rearrangement in the 3‐(4′‐aryloxybut‐2′‐ynyl)mercapto‐5,5‐dimethyl cyclohex‐2‐enones afforded a number of 4‐aryloxymethyl‐7,7‐dimethyl‐6,7,8‐trihydrothiochrom‐3‐en‐5‐ones (70–80%), which underwent second [3,3]sigmatropic rearrangement to furnish benzofuro[3,2‐c][1]‐2,3,4,6,6a,11a‐hexahydro‐3,3,11a‐trimethylthiobenzopyran‐2‐ones (60–70%).     

Regioselective Synthesis of α‐Iodoacetates from Alkenes/Ammonium Acetate/I2 by Woodward's Reaction

Abstract

Regioselective synthesis of α‐iodoacetates from alkenes, ammonium acetate, and iodine in acetic acid is reported. The reaction is facile, fast, environmentally, friendly, and cost effective. α‐Iodoacetates are obtained from both acyclic and cyclic alkenes in high yields ranging from 80–95% within 10–20 min.     

Chiral Synthesis of the Key Intermediate of Diterpenoids

(-)-Methyl(4R,5SloR)-l4-methoxyPodocmpa-8,ll,l3-triene-l9-oate(I)isthekeyintermediateforsynthesesofditerpenoidssuchaskaurenoicacid(3),kaur-l6-en-l9-ol(4),monoginol(5)('),aswellasC,,-diterpenealkaloidssuchasveachine(6),garryine(7)andatisine(8)(=).TheracemicsynthesisofthisintermediatewasdonebyK.Morietar'),butthechiralsynthesishasnotbeenreported.Herewepresentthechiralsynthesisofthiskeyintermediatefrom(R)-(+)-2-methyl-2-(2'-nitrovinyl)-5-vaierolactone(2).2wassynthesizedaccordingtoliterattirmeth…     

Novel Synthesis of N‐Methyl Spiropyrrolidines by 1,3‐Dipolar Cycloaddition Reaction of Azomethine Ylides

A series of novel N‐methyl spiropyrrolidines have been synthesized in good yield by the cycloaddition reaction of azomethine ylides generated by a decarboxylative route from sarcosine and paraformaldehyde with conformationally locked s‐trans enone functionality present in the (E)‐3‐arylidene‐4‐chromanone as dipolarophiles. The structure of the title compound was established by spectroscopic techniques.     

Electroreduction of Mo(VI) Compounds in Ammonium–Acetate Solutions

The kinetics of cathodic reactions in ammonium acetate solutions proposed for electrodeposition of metallic molybdenum was studied. The reduction of molybdenum compounds in the oxidation state +6 was found to occur stepwise according to the scheme Mo(VI) → Mo(V) → Mo(III). The waves observed on the polarograms are complicated by adsorption effects. The reduction of molybdenum to the metallic state is possible only at high negative potentials of the cathode; under the polarographic analysis conditions, this wave was not recorded. The deposit that formed on the surface of the solid cathode during cathodic polarization (i = 0.5 A cm^–2) contains both molybdenum in the metallic state and molybdenum oxides. The ratio between the electrolysis products depends on the temperature of solution: a decrease in the temperature leads to an increase in the amount of metallic molybdenum.

     

Ramberg-Baecklund Rearrangement Approaches to the Synthesis of Natural Bibenzyls

The Ramberg-Baecklund rearrangement has been successfully utilized to convert readily available α-and α‘-hydrogen bearing substituted dibenzyl sulfones into corresponding stilbene derivatives, which is conveniently followed by hydrogenation in the presence of 10% Pd/C to afford the natural bibenzyls.     

[2,3]-Wittig Sigmatropic Rearrangement of Steroidal 16β-Propargyl Ethers for the Synthesis of 25-Hydroxyvitamin D Side Chain Analogues

An efficient [2,3]-Wittig sigmatropic rearrangement of the pregnadiene derivative 2b allowed the one-step introduction of a side chain with the natural (20R) chirality and the 25-hydroxy group of the principal metabolites of vitamin D.     

The Rearrangement of 2—Benzothiazolylthioacetyl Hydrazide in Synthesis of s—Triazolo[3,4—b]benzothiazole—3—thiol

The rearrangement reaction of 2-benzothiazolylthioacetyl hydrazide 1 with potassium hydroxide and carbon disulfide in ethanol to produce s-triazolo [3,4-b] benzothiazole-3-thiol 3 was described. 3 also can be obtained from 2-benzothiazolylhydazine 2 and the two methods for getting 3 were compared. Mannich reaction of compounds 3 was reported too.     

The Dimroth Rearrangement in the Synthesis of Condensed Pyrimidines – Structural Analogs of Antiviral Compounds

Chemistry of Heterocyclic Compounds - The review discusses the use of the Dimroth rearrangement in the synthesis of condensed pyrimidines which are key structural fragments of antiviral agents. The...     

Single-Pot Synthesis of Spiroannulated Dihydrofurans by Iodine–Ammonium Acetate–Mediated Reaction of Dimedone with Aldehydes

Iodine–ammonium acetate–mediated annealation of dimedone with aldehydes led to facile formation of spirodihydrofuran in good yields through tandem Knoevenagel–Michael iodonation and cyclodehydroiodonation reactions in a single pot.     

Synthesis of Methyl α-D-Kijanoside

Abstract

In 1981, Mallams and coworkers reported¹ the discovery of - D-kijanose 1, a branched-chain nitro sugar, isolated from the antitumor antibiotic kijanimicin by acid hydrolysis. The structure of this unusual carbohydrate was established ^1,2 as 2,3,4,6-tetadeo xy-4 - (methoxy carbony1 amino 1-3-c-methyl - 3 -nitro - D-xylo-hexopyranose by spectroscopic and crystallographic analysis, and comparison with D-rubranitrose 2, a carbohydrate found in the antibiotic rubradirin .³Two other nitro sugars, L-evernitrose 3 and - L-decilonitrose 4⁵, have been discoveredas components of antibiotics.     

Synthesis and Transesterification of the Complexes of Methyl 2-Methyl-3-trichlorostannylpropoinate with Benzylmethylsulfoxide

2-Methyl-3-trichlorostannylpropionate, Cl3SnCH2CH(CH3)CO2R, a novel type of mono- organotin compounds containing ester group, have received considerable attention since Hutton et al. reported their synthesis because of the variety of coordination geometry about tin atom1-4. Organotin compounds5 like organotin carboxylates or oxides were already used as transesterification catalysts, however, little attention was paid to transestrifications of 2-methyl-3-trichlorostannylpropionate complexe…     

Total Synthesis of Resorcylic Acid Lactone (−)-Neocosmosin A Using Palladium-Catalyzed α-Arylation of Enones as the Key Step

The total synthesis of the 14-membered resorcylic acid lactone neocosmosin A is described. The key step in the synthesis is the palladium-catalyzed α-arylation of TES-enol ethers of enones. The employment of the α-arylation approach to this class of resorcylic acid lactones is a new approach, which has the scope of being generalized into a unified approach for the synthesis of this class of natural products.     

One Step Synthesis of 2′-Thiobiotin From 2-Biotin

A one step synthesis of 2′-thiobiotin by direct sulfuration of 2′-biotin is described.