Enolizable Protons Research Articles

ChemInform Abstract: Rapid Synthesis and Antimicrobial Activity of Novel 4‐Oxazolidinone Heterocycles.

AbstractOxazolidinone derivatives (VI) are synthesized by a one‐step dehydration/cyclization reaction of α‐keto amides (IV) bearing enolizable protons.

Iodine-Catalyzed Aza-Diels–Alder Reactions of Aliphatic N-Arylaldimines

Iodine-catalyzed aza-Diels–Alder (Povarov) reaction of 3,4-dihydro-2H-pyran with in situ generated N-arylimines containing enolizable protons is described. This has given an easy way to introduce C-2 aliphatic substitution in tetrahydroquinolines.

Diastereoselective and Enantioselective Rh(I)‐Catalyzed Additions of Arylboronic Acids to N‐tert‐Butanesulfinyl and N‐Diphenylphosphinoyl Aldimines.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A General Method for the Preparation of N‐Sulfonyl Aldimines and Ketimines.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Deuterium Exchange in Ethyl Acetoacetate: An Undergraduate GC–MS Experiment

A simple experiment involving deuterium exchange of the enolizable protons in ethyl acetoacetate followed by GC–MS has been developed. The principles demonstrated are the use of stable isotopes, keto–enol tautomerism, base catalysis, and the use of specific reagents to minimize or nullify side reactions. The changes in mass of specific fragment ions, as well as that of the molecular ions are indicative of the course of the reaction and illustrative of the fragmentation pathways. The acidity of the methylene hydrogens of the acetoacetate moiety is exploited in the acetoacetic ester synthesis of alkyl-substituted acetones. These readily exchange under very mild conditions. More challenging is to exchange all five enolizable hydrogens. Use of increasingly severe reaction conditions leads to side reactions, such as deuterolysis of the ester portion if D2O is used. The solution was to use ethanol O–d as the source of deuterium and KOD for the base for the exchange reaction and moderate heat. The role of ethanol O–d in nullifying the deuterolysis is demonstrated by determining that trans-esterification of methyl acetoacetate to the ethyl ester occurs as well as deuterium exchange of the five acetoacetate hydrogens.

Diastereoselective and Enantioselective Rh(I)-Catalyzed Additions of Arylboronic Acids to N-tert-Butanesulfinyl and N-Diphenylphosphinoyl Aldimines

Two new Rh(I)-catalyzed methods for the synthesis of chiral alpha-branched amines via addition of arylboronic acids to N-tert-butanesulfinyl and N-diphenylphosphinoyl imines have been developed. The syntheses are more functional group tolerant than alternative methods utilizing Grignard or organolithium reagents, and the imine activating groups used are easily removed. These methods are both high-yielding (70-97% yield) and very selective (>93:7 dr and 88-94% ee). Significantly, the N-tert-butanesulfinyl imine method works for aliphatic imines with enolizable protons. In addition, a one-pot procedure for the synthesis of N-tert-butanesulfinyl protected alpha-branched amines from aldehydes has been developed.

A General Method for the Preparation of N-Sulfonyl Aldimines and Ketimines

[Reaction: see text] A simple procedure to obtain N-sulfonyl imines involving the condensation of carbonyl compounds with p-tolyl or tert-butyl sulfinamides followed by oxidation with m-CPBA of the resulting N-sulfinylimines is reported. The method is applicable to aldehydes (aliphatics and aromatics) and ketones (diaryl, dialkyl, and aryl alkyl), even those containing enolizable protons. It also does not affect C=N or C=C double bonds and does not epimerize alpha-stereogenic centers.

Gas-phase synthesis and reactivity of the organomagnesates [CH3MgL2]- (L = Cl and O2CCH3): from ligand effects to catalysis.

Multistage mass spectrometry experiments combined with density functional theory (DFT) calculations were used to examine the gas-phase synthesis and ion-molecule reactions of the organomagnesates [CH(3)MgL(2)](-) (L = Cl and O(2)CCH(3)). Neutral species containing an acidic proton (HX) react with the [CH(3)MgL(2)](-) ions via addition with concomitant elimination of methane to form [XMgL(2)](-) ions. Kinetic measurements combined with DFT calculations revealed reduced reactivity of [CH(3)Mg(O(2)CCH(3))(2)](-) toward water, caused by the bidentate binding mode of acetate, which induces overcrowding of the Mg coordination sphere. The [CH(3)MgL(2)](-) ions reacted with (i) aldehydes with enolizable protons via enolization rather than the Grignard reaction and (ii) CH(3)CO(2)H to complete a catalytic cycle for the decarboxylation of acetic acid. Other electrophilic reagents such as pivaldehyde, benzaldehyde, methyl iodide, and trimethylborate are unreactive. DFT calculations on the competition between enolization and the Grignard reaction for [CH(3)MgCl(2)](-) ions reacting with acetaldehyde suggest that while the latter has a smaller barrier, it is entropically disfavored.

Lanthanide(III)-catalyzed multi-component aza-Diels–Alder reaction of aliphatic N-arylaldimines with cyclopentadiene

Abstract The Ln(OTf) 3 -catalyzed formal aza-Diels–Alder (or Povarov) reaction of cyclopentadiene with in situ generated N -arylimines containing enolizable protons is described. This three-component Povarov reaction generates highly functionalized C-2 aliphatic substituted tetrahydroquinolines, heterocycles that were previously inaccessible using the Povarov reaction, because of the instability of the intermediate aliphatic N -arylaldimine.

Spectroscopic studies of the electrophilic activation of amides with triflic anhydride and pyridine

The reaction of amides with trifluoromethanesulfonic (triflic) anhydride in the presence of pyridine was thoroughly investigated by NMR spectroscopic techniques. Different pyridinium intermediates were generated from secondary amides, tertiary amides with enolizable protons, and tertiary amides lacking enolizable protons. It was found that the actual triflating reagent is N-(trifluoromethylsulfonyl)pyridinium triflate 11 which is formed by the initial reaction of triflic anhydride with pyridine. The alcoholysis of these intermediates yields O-alkyliminium ethers which can then be easily hydrolyzed under mild acidic conditions to the corresponding esters.Key Words: amides, triflic anhydride, pyridinium intermediates, NMR study.

Reduction of Imines via Titanium-Catalyzed Hydromagnesation

We have recently discovered that imines can be reduced to amines via a titanium catalyzed hydromagnesation reaction. These reactions employ n-BuMgCl (1.2 eq) as the stoichiometric reducing agent and Cp 2TiCl 2 (3–5 mol%) as a catalyst. Reactions are run under nitrogen at ambient temperature and pressure. For most aldimine and cyclic ketimine substrates amine products are obtained in yields ranging from 69–94%. The reaction is not tolerant of bulky nitrogen substituents or primary enolizable protons on the imine substrate. © 1997 Elsevier Science Ltd.

Chromophore formation in polyarylate diacetate chemistry

It is found that color formation during the condensation polymerization of aromatic diacids with bisphenol A diacetate results from a low level ring acylation side reaction during the ester derivatization of bisphenol A with an anhydride having enolizable protons. Substitution of the enolizable protons, e.g., trifluoroacetic acid, results in low color polyarylates

Scope and Limitations in the Use of α-Silyl and α-Stannyl Sulfones as Latent α-Sulfonyl Anions

Abstract Three methods for the regeneration of α-sulfonyl anions from α-silyl sulfones and α-stannyl sulfones are investigated. These methods include: (1) treatment of α-silyl sulfones with electrophiles (aldehydes and acid halides) in the presence of fluoride ion; (2) reaction of α-silyl sulfones with n-butyllithium which produces an α-silyl anion via a migration of the -SiMe3 group from the α-position to the ortho-position of the phenyl sulfones; and (3) direct transmetalation of α-stannyl sulfone by treatment with n-butyllithium. The addition of cerium [III] chloride is shown to substantially decrease enolization problems associated with addition of α-sulfonyl anions to carbonyl compounds bearing enolizable protons.

Intramolecular acylation of an α-sulfonyl anion generated via halogen-metal exchange of an α-halosulfone bearing an unsymmetrical anhydride

α-Halosulfones are useful for the in situ preparation of α-sulfonyl anions in the presence of acylating agents bearing enolizable protons. Inter- and intramolecular acylations can be effected by halogen-metal exchange at low temperature.