Highly Efficient InBr3 Catalyzed Michael Addition of Indoles to α, β-Unsaturated Esters

A highly efficient synthetic strategy toward Michael addition of indoles to α,β‐unsaturated esters has been developed using Lewis acid InBr₃ as catalyst. The reactions generated 3‐substituted indoles in high yields with excellent regio‐selectivity in the presence of catalytic amount of InBr₃ under mild reaction conditions. The method is simple, efficient and practical.     

Efficient Synthesis of Polyethylene Glycol Mono‐Carboxylate via Michael Conjugate Addition

Abstract

Poly(ethylene glycol) (PEG) with one carboxylate group, the very useful precursors for the synthesis of the PEG derived heterobifunctional linkers, are synthesized in high yield in one‐pot via Michael conjugate addition of acrylate esters with PEG and catalyst amount of sodium in THF.     

Generation of α-Boryl Radicals and Their Conjugate Addition to Enones: Transition-Metal-Free Alkylation of gem-Diborylalkanes

A transition-metal-free method for the alkylation of gem-diborylalkanes with α,β-unsaturated ketones has been developed. It is demonstrated that the α-boryl radicals can be generated efficiently from gem-diborylalkanes with the aid of catechol and oxidants. The α-boryl radicals formed through such process can be engaged in conjugate addition reaction with α,β-unsaturated ketones. This transformation is a straightforward method for the synthesis of γ-borylketones.     

Copper(II) Bromide–Catalyzed Conjugate Addition of Indoles to α,β‐Enones

Copper(II) bromide was found to be an efficient catalyst for the conjugate addition of indoles to α,β‐enones in acetonitrile at room temperature.     

Enantioselective Construction of 3-Hydroxy Oxindoles via Decarboxylative Addition of β-Ketoacids to Isatins

The first highly enantioselective decarboxylative addition of β-ketoacids to isatins mediated by a bifunctional tertiary amine-thiourea catalyst has been developed, allowing facile synthesis of biologically important 3-hydroxy oxindoles in good yields and excellent enantioselectivities. The method reported represents a valuable approach of utilizing β-ketoacids as synthetic equivalents of aryl/alkyl methyl ketone enolates.     

Charge-Directed Conjugate Addition Reactions of Salts of Unsaturated β-Keto-Esters

Strong nucleophiles undergo conjugate addition reactions with enolates of Nazarov-type reagents. Yields are strongly affected by substitution patterns and the metal cation employed.     

Enantioselective Addition of Diethylzinc to Aromatic Aldehydes Catalyzed by Pyrolidine and Piperidine β-Amino Alcohols

The enantioselective alkylation of aryl aldehydes by diethylzinc in the presence of catalytic amounts of several chiral pyrolidine- and piperidine-based amino alcohol ligands, synthesized from the reaction of (R)-2-amino-1-butanol and (S)-2-amino-3-phenylpropan-1-ol with appropriate dibromoalkanes, was studied. The influence of temperature and ligand structure has been investigated. Addition of diethylzinc to aromatic aldehydes under the optimized condition gave the corresponding products in excellent yields with ee values of up to 77%.     

Conjugate Addition of Anions of Protected Cyanohydrins to β-Nitro-Styrene and Some Synthetic Applications of the Resulting Adducts

Some time ago one of us participated in the development of the acyl anion equivalent: the anions of protected cyanohydrins¹. Looking for new possibilities for these reagents, we have now examined their reaction with β-nitro-styrene and found that the resulting adducts are versatile intermediates, useful for a number of conversions of synthetic importance².     

Atom Economic and Highly Syn‐selective Prolinamide‐Catalyzed Cross‐aldol Addition of Hydroxyacetone to Aromatic Aldehydes

The highly selective cross‐aldol addition of hydroxyacetone (HA) to p‐nitro and m‐nitrobenzaldehyde is reported; the reaction is catalyzed by three different di‐ or tripeptides all containing D‐Pro in the N‐terminal position and one or two residues of β³‐homophenylglycine (β³‐hPhg): H‐D‐Pro‐(R)‐β³‐hPhg‐OBn, H‐D‐Pro‐(R)‐β³‐hPhg‐(S)‐β³‐hPhg‐OBn and H‐D‐Pro‐[(S)‐β³‐hPhg]₂‐OBn. Several reaction conditions have been tested, always in the absence of a protecting group on the HA hydroxyl. This reaction affords the desired compounds with complete regioselectivities being the other regioisomer completely avoided. Furthermore high enantioselectivities and satisfactory diastereoselectivities, always favouring the syn diastereoisomers, were obtained. The stereochemistry of the diols was further confirmed by the analysis of the ¹H NMR spectrum of the corresponding carbonates, obtained by reaction of the syn/anti mixtures with triphosgene in presence of dimethylamino‐pyridine (DMAP).     

Organocatalytic Conjugate Addition of Azide Ion to α,β‐Unsaturated Aldehydes

An efficient and simple amine‐catatalyzed azide conjugate addition to α,β‐unsaturated aldehydes has been developed. In the presence of a catalytic amount of tertiary amine with a 1:1 mixture of NaN₃ and 37% HCl in CH₂Cl₂, α,β‐unsaturated aldehydes provided β‐azido aldehydes, which could be transformed into 1,3‐amino alcohols.     

Catalytic Asymmetric Conjugate Addition of Indolizines to α,β-Unsaturated Ketones

A catalytic enantioselective conjugate addition of indolizines to enones is described. The chiral phosphoric acid (S)-TRIP activates α,β-unsaturated ketones, thereby promoting an enantioface-differentiating attack by indolizines. Using this reaction, several alkylated indolizines were synthesized in good yields and with enantiomeric ratios of up to 98:2.     

Efficient Syntheses of 1H-Isochromen-1-Ylmethylphosphonates via Regioselective 6-Endo-Dig Addition to Carbon—Carbon Triple Bond Catalyzed by Pd(OAc)2

Abstract

An efficient, regioselective, palladium-catalyzed intramolecular cycloisomerization of dialkyl [(2-(2-ethynyl)phenyl)(2-hydroxyl)ethyl]phosphonate 6 is reported. The reactions proceed through a 6-endo-dig cyclization to afford 1H-isochromen-1-ylmethylphosphonates 7 in good to excellent yields using palladium(II) acetate as the catalyst in tetrahydrofuran at room temperature.

[Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements for the following free supplemental resource: General Comments. Figures S1–S33.]

GRAPHICAL ABSTRACT      

Addition of Organocuprates to Ketoketenimines. Synthesis of β-enaminoketones

Base-induced ring cleavage of 3-unsubstituted isoxazolium salts followed by reaction of the resulting ketoketenimine with organocuprates affords asymmetric β-enaminoketones in high yields.     

Syntheses of Thailandepsin B Pseudo-Natural Products: Access to New Highly Potent HDAC Inhibitors via Late-Stage Modification

New Thailandepsin B pseudo-natural products have been prepared. Our synthetic strategy offers the possibility to introduce varying warheads via late stage modification. Additionally, it gives access to the asymmetric branched allylic ester moiety of the natural product in a highly diastereoselective manner applying rhodium-catalyzed hydrooxycarbonylation. The newly developed pseudo-natural products are extremely potent and selective HDAC inhibitors. The non-proteinogenic amino acid d -norleucine was obtained enantioselectively by a recently developed method of rhodium-catalyzed hydroamination.     

Cadmium Chloride (CdCl2): An Efficient Catalyst for Conjugate Addition of Amines to Electron‐Poor Alkenes

Electron‐deficient olefins undergo rapid Aza–Michael reaction with a wide range of amines catalyzed by cadmium chloride at room temperature.     

Efficient Syntheses of 2-Substituted Benzimidazoles and Benzoxazoles from β-Keto Esters

An efficient synthetic method was developed to synthesize 2-substituted benzimidazoles and benzo- xazoles with β-keto esters as starting materials under mild reaction conditions, during which other functional groups are bearable from reactants to products.     

Conjugate Addition of a Silyl Ketene Acetal to α,β‐Unsaturated Lactones

Abstract

Conjugate addition of a silyl ketene acetal [Me₂C?C (OMe)OSiMe₃] to α,β‐unsaturated lactones (namely, 5,6‐dihydro‐2H‐pyran‐2‐one, 2(5H)‐furanone as Michael acceptor) occurs efficiently at room temperature in the presence of a nucleophilic catalyst, tetra‐n‐butyl ammonium bibenzoate (TBABB), in THF as well as Lewis acid catalysts such as Yb(OTf)₃ and I₂ in CH₂Cl₂, giving the corresponding 1,4‐adducts in excellent yields.