A facile two-step chemoenzymatic access to natural germination inhibitor (+)-erigeronic acid A

A facile two-step synthesis of natural germination inhibitor 5-butyl-3-oxo-2,3-dihydrofuran-2-yl-acetic acid [(+)-erigeronic acid A, 1] has been described via highly regioselective ring opening of (R)-acetoxysuccinic anhydride with the primary enolate of butyl methyl ketone, followed by an enzymatic hydrolysis and an in situ dehydrative cyclization pathway with 77% overall yield. On the basis of the present chemoenzymatic approach, (R)-configuration has been assigned to the C-2 chiral centre of the natural erigeronic acid.     

An unexpected reaction of pyridine with acetyl chloride to give dihydropyridine and piperidine derivatives

An unexpected reaction of pyridine with acetyl chloride to give N-acetyl-1,2 and 1,4-dihydropyridyl acetic acid (1, 2) in high yield and regioselectivity has been reported. The key step is the formation of a zwitterionic pyridinium ketene enolate. The effect of different activating agents on the reaction yield and selectivity has been studied. Platinum(IV) mediated hydrogenation of the corresponding methyl esters (7, 8) gave piperidine derivatives (9, 10).     

Mannich‐Type Reaction Catalyzed by Silica‐Supported Fluoroboric Acid under Solvent‐Free Conditions

Three‐component Mannich‐type reaction of aldehydes, aromatic amines, and silyl enolate proceeded smoothly to afford β‐amino carbonyl compounds with good yields in the presence of a catalytic amount of HBF₄‐SiO₂.     

Synthesis of 1-Acyl-3-Piperidones

The 1-acyl-3-piperidones ( 5 and 8 ) have been synthesised from N-benzylpiperidine-3,5-dione ( 1 ) via a reaction sequence, which is shown to be of general utility for the preparation of 1-acyl-3-piperidones. The total yields of 5 and 8 obtained from 1 are 35% and 31% respectively.     

Design,synthesis and crystallographic study of novel indole‐based cyano derivatives as key building blocks for heteropolycyclic compounds of major complexity

A four‐stage reaction sequence has been designed and developed for the synthesis of highly functionalized enolate esters as key building blocks for the synthesis of novel heteropolycyclic compounds of potential pharmaceutical value. The sequence starts with simple commercially available indoles and proceeds via 3‐(indol‐3‐yl)‐3‐oxopropanenitriles, which react with 2‐bromobenzaldehyde to form the corresponding chalcones; these are readily reduced to dihydrochalcones, which are in turn acylated to form the enolate esters. The compounds in this sequence have been characterized by IR and ¹H and ¹³C NMR spectroscopy, by mass spectrometry and by elemental analysis. The molecular and supramolecular structures are reported for representative examples, namely (E )‐3‐(2‐bromophenyl)‐2‐(1‐methyl‐1H‐indole‐3‐carbonyl)acrylonitrile, C₁₉H₁₃BrN₂O, (Ib ), (2RS )‐2‐(2‐bromobenzyl)‐3‐(1‐methyl‐1H‐indol‐3‐yl)‐3‐oxopropanenitrile, C₁₉H₁₅BrN₂O, (IIb ), and (2RS )‐3‐(1‐benzyl‐1H‐indol‐3‐yl)‐2‐(2‐bromobenzyl)‐3‐oxopropanenitrile, C₂₅H₁₉BrN₂O, (IIc ), the latter two of which crystallize with Z ′ = 2, and (E )‐1‐(1‐acetyl‐1H‐indol‐3‐yl)‐3‐(2‐bromophenyl)‐2‐cyanoprop‐1‐en‐1‐yl acetate, C₂₂H₁₇BrN₂O, (III), and (E )‐1‐(1‐benzyl‐1H‐indol‐3‐yl)‐3‐(2‐bromophenyl)‐2‐cyanoprop‐1‐en‐1‐yl benzoate, C₃₂H₂₃BrN₂O, (IV). The structure of the related chalcone (E )‐2‐benzoyl‐3‐(2‐bromophenyl)prop‐2‐enenitrile, (V), has been redetermined at 100 K, where it is monoclinic, as opposed to the triclinic form reported at ambient temperature.     

Palladium-catalyzed asymmetric allylic alkylation of acyclic ketones for synthesis of 2,2-disubsituted pyrrolidine derivatives

Palladium-catalyzed asymmetric allylic alkylation of acyclic ketones represents a significant challenge in organic synthesis. We report herein that the synthesis of chiral 2,2-disubsituted pyrrolidines from acyclic ketones has been accomplished by using catalytic asymmetric method in the presence of Pd(dba)₂ and (R)-binap ligand. Theses reactions occur between allyl methyl carbonate and unstabilized acyclic lithium enolates to provide the products in moderate to good enantioselectivity (up to 81% ee).     

Photoinitiated Reaction of β-Bromonaphthalene with Pinacolone Ion in DMSO

The radical nucleophilic substitution reaction (SRN1) has been studied widely. The reaction has constituted an important synthetic possibility to achieve substitution of different substrates with different nucleophiles1-3. The main steps of the reaction process are presented in Scheme 1.Scheme 1. Pinacolone enolate ions are widely used as nucleophiles within SRN1reaction 4-6 because it can introduce six carbon atoms into substitution products. In the paper, the photoinitiated reaction of …     

Indium(III)-catalyzed intramolecular addition of silyl enolates to alkynes

In the presence of water and a catalytic amount of InBr₃, intramolecular trans-addition of silyl enolates derived from ketones and an aldehyde to alkynes proceeded smoothly to give 4 to 7-membered carbocycles bearing an acyl group. When carboxylic anhydrides were used as electrophiles instead of water, the cyclized products could be functionalized with an additional acyl group.     

First Isolation and Characterization of the Highly Coordinated Group 14 Enolates: Effects of the Coordination Controls on the Geometry and Tautomerization of Germyl Enolates

The Group 14 enolates play an important part in many organic reactions. Herein, the reduction of an α‐bromo ketone with germanium(II) salts cleanly afforded the corresponding germyl enolate as an isolatable species. This experimental reductive generation of a germyl enolate enabled us to characterize both C‐ and O‐bound tautomers derived from an identical precursor and to unveil the tautomeric mechanisms, including the kinetic parameters and the relative stability of these tautomers, along with confirmation from DFT calculations. Moreover, the highly coordinated germyl enolates were isolated by a stabilization process induced by adding ligands. All products were characterized by NMR spectroscopy and X‐ray crystallography.