Enolic OH Research Articles

Crystal structure, tautomerism and photostability of 2-(2-pyridyl)-phenalene-1,3-dione

Tautomerism of cyclic β-diketones has been of scientific interest for decades due to the practical applications it can render, from sensors to photostable materials. In this work the tautomerism of 2-(2-pyridyl)-phenalene-1,3-dione (PPD) was studied in solid state, in solution, and in gas phase through a combination of experimental and theoretical methods. Single-crystal X-ray diffraction analysis of PPD revealed its existence in diketo form in the solid state with protonated pyridyl nitrogen that is stabilized by the intramolecular hydrogen bond of N-H···O type. A very large Stokes shift was observed in the emission spectra in DMSO (ca. 177 nm) and in ethanol (ca. 160 nm), indicating on possible excited-state intramolecular proton transfer (ESIPT) process. DFT calculations in ground state (gas phase and water medium) and in the excited singlet state (B3LYP-6311++G(d,p)) agree very well with the experimental data and suggest reverse order of the possible OH and NH tautomers in the ground and the excited singlet state, namely the diketo NH tautomer is the most stable one in the ground state whereas in the excited singlet state the enol OH form is more stable. The photostability of PPD was estimated by irradiation experiments that were performed in comparison with 2-acetylindan-1,3-dione (2AID), which is a compound with proven high photostability in ethanol and fast ESIPT. The data showed that unlike 2AID, the 2-(2-pyridyl)-phenalene-1,3-dione exhibits lower photostability in ethanol. These results could suggest that either the ESIPT process is not the only transformation that takes place in the excited state of PPD, or it is not as fast as the one of 2AID.

Kinetic Study of Lornoxicam Hydrolysis

Gastrointestinal tract (GIT) side effects due to the local action of lornoxicam considered the most common problem that associated with using of this analgesic drug. Masking of the enolic alcohol OH group of lornoxicam to overcoming this problem was the aim, however, applying Williamson ether synthesis led to amide hydrolysis. Therefore, the objective of this study was shifted to study the hydrolytic kinetics and the influence of different bases as a function of time and temperature in the reaction media. The effects of all bases used in the study on the hydrolysis process of lornoxicam have been studied; NaOH was found to be the strongest followed by Na2CO3 and K2CO3. All three temperatures (25°C, 50°C and 80°C) have approximately similar effect  except  reflux condition that accelerates the hydrolysis process compare with the others. The hydrolysis process is proportional with time. Williamson ether synthetic procedure that followed to synthesize lornoxicam prodrugs was failed despite attempting different conditions. Using bases were induced the hydrolysis process of lornoxicam. The hydrolysis rate accelerated under reflux more than other conditions. In addition, reaction time gives more hydrolysis process.

Structural characterization, thermal investigation and biological activity of metal complexes containing Schiff Base ligand (Z)‐3‐(1‐((4,6‐dimethyl‐1H‐pyrazolo[3,4‐b] pyridin‐3‐yl)imino)ethyl)‐4‐hydroxy‐6‐methyl‐2H‐pyran‐2‐one

A new series of metal complexes containing Co(II), Pd(II), Fe(III) chloride and Cu(II) salts (chloride, bromide, sulphate and perchlorate) have been prepared with Schiff base ligand (HL). The synthesized compounds were elucidated using elemental analyses, spectral techniques, molar conductance, magnetic measurements and thermogravimetric studies. The analytical data established (1 M:1 L) stoichiometry for complexes (1), (2), (4), (6) and (7) as well as (1 M:2 L) and (2 M:3 L) stoichiometry for complexes (5) and (3), respectively. As a result, the ligand HL coordinates in complexes (1), (2), (4), (6) as a monobasic tridentate ONN moiety via the oxygen atom of the deprotonated phenolic OH, the nitrogen atoms of the azomethine and the imine group in pyrazolopyridine ring. While, it behaves as a neutral bidentate in complexes (3,7), chelates via oxygen and nitrogen atoms of enolic OH and azomethine groups. Also, in complex (5) Cu2+ ion binds via NO sits of two ligand molecules in its monobasic and neutral forms. The magnetic moment and electronic spectral data proposed octahedral structure for complexes (2, 3 and 7) as well as triagonal bipyramidal and square pyramidal geometry for complexes (1 and 4), while, chelates (5) and (6) possess square planar geometry. TG/DTG studies confirmed the chemical formula for these complexes and established the thermal decomposition processes ended with the formation of metal or metal oxides contaminated with carbon residue. An axial electron spin resonance spectra were suggested for Cu(II) complexes pointing to 2B1g as a ground state with hyperfine structure for complex (4). In vitro antibacterial and antioxidant activities were performed for HL ligand and its metal complexes. The biological studies indicate that complex (3) has better antibacterial activity compared to the ligand and the other complexes.

Correction to Discovery of the Hemifumarate and (α-l-Alanyloxy)methyl Ether as Prodrugs of an Antirheumatic Oxindole: Prodrugs for the Enolic OH Group.

Ether, ester, and carbonate derivatives of the antirheumatic oxindole 1 were prepared and screened as potential prodrugs of 1. This effort led to the discovery of the (alpha-L-alanyloxy)-methyl ether and hemifumarate derivatives of 1 which deliver the drug efficiently into the circulation of test animals, are stable in the solid state, and possess good stability in solution at low pH as required to ensure gastric stability. Success in achieving acceptable bioavailabilities of 1 across species (rats, dogs, and monkeys) followed the inclusion of ionizable functionality within the promoiety to compensate for masking the polar enolic OH group of the free drug. However, the introduction of ionizable functionality was often associated with decreased stability, as demonstrated by the hemisuccinate, hemiadipate, hemisuberate, and alpha-amino ester derivatives of 1 which could not be isolated. A clear exception was the hemifumarate derivative of 1 which was not only isolable but actually more stable at neutral pH than the nonionizable ester analogues. The solution and solid state stability of the hemifumarate, together with its activity as a prodrug of 1, suggests that hemifumarate be considered as an alternative to hemisuccinate as a prodrug derivative for alcohols, particularly in situations where solution state stability is an issue.

Polymer complexes. LXIX. Some divalent metal(II) polymer complexes of potentially bidentate monomer N‐[4‐(5‐methyl‐isoxazol‐3‐ylsulfamoyl)‐phenyl]‐acrylamide: Synthesis, spectroscopic characterization, thermal properties, antimicrobial agents and DNA studies

Monomer of N‐[4‐(5‐methyl‐isoxazol‐3‐ylsulfamoyl)‐phenyl]‐acrylamide (HL) and some transition metal polymeric complexes of the general formula {[M(HL)(OH2)2(OCOCH3)2] xH2O}n (M = Co(II), x = 2; Ni(II), x = 3; Mn(II), x = 2) and [Cd(HL)2(OCOCH3)2] were synthesized and characterized by elemental analysis, IR, UV spectroscopy, conductance measurements, magnetic susceptibility, thermogravimetric analyses and X‐ray diffraction analysis. In all polymer complexes, the spectral data revealed that the ligand act as bidentate neutral molecule and coordinate to metal ion through enolic sulphonamide OH and isoxazol‐N. In all polymer complexes, the spectral data revealed that the ligand act as bidentate neutral molecule and coordinate to metal ion through enolic sulphonamide OH and isoxazol‐N. The molar conductance data revealed that the polymer complexes are non‐electrolytes while UV‐vis and magnetic measurements data have been shown that the polymer complexes have octahedral geometry. All the studies revealed coordination six for the metals in all the polymer complexes and octahedral structures were suggested. The inhibitive effect of HL against C38 steel was investigated in 2 M HCl solution (tafel polarization, electrochemical impedance spectroscopy (EIS) and electrochemical frequency modulation (EFM) methods). The type of HL is mixed inhibitor whose adsorption habit onto C38 steel.

New Insight into and Characterization of the Aqueous Metal-Enol(ate) Complexes of (Acetonedicarboxylato)copper.

Nearly 50 years have passed since the classic studies by Larson and Lister [LarsonD. W.; ListerM. W.Can. J. Chem.1968, 46, 823]and Hay and Leong [HayR. W.; LeongK. N.J. Chem. Soc. A1971, 0, 3639]on the copper-catalyzed decarboxylation of acetonedicarboxylic acid (H3Acdica). Although the authors laid the foundations for what we know about this reaction; still very little information exists regarding the underlying aqueous metal-enol(ate)s of (acetonedicarboxylato)copper. In this study, UV–visible titrations revealed three pK values, pK[Cu(H2A)], pK[Cu(HA)], and pK[Cu(A)]. We associated the first two with ionization of α-carbon CH2 groups in [CuII(H2Acdica)keto]1+ and [CuII(HAcdica)keto]0 to form unstable metal-enolates, {[CuII(HAcdica)enolate]} and {[CuII(Acdica)enolate]}, which through β-carbonyl oxygen protonation can form metal-enols [CuII(H2Acdica)enol]1+ and [CuII(HAcdica)enol]0. The square-planar CuII center (electron paramagnetic resonance results) plays a dual role of stabilizing negative electron density at the β-carbonyl oxygen and as an electron sink in [[CuI(HAcdica)enolate]0]‡ and [[CuI(Acdica)enolate]1–]‡ (confirmed through cyclic voltammetry as two single 1e– transfers). The π → π* transition associated with [CuII(HAcdica)enol]0 was used to determine pK[Cu(A)] (deprotonation of enol OH) and enolization rate constant (stopped-flow spectroscopy) but also exhibited a time-dependent decrease in absorbance (on the order of min–1), suggesting a new method to possibly obtain experimental values for the estimated “kCuL” decarboxylation rate constant of metal-enolate [CuL]1– calculated by Larson and Lister. On the basis of our results, we postulate that decarboxylation takes place primarily through {[CuII(HAcdica)enolate]} and [CuII(HAcdica)enol]0. These results add to our understanding of aqueous metal-enol(ate)s, which contain underlying CuII/I redox chemistry, “active methylenes” and enol tautomers and enolate anions, which play roles in many catalytic reactions of interdisciplinary importance.

Alkyl chain length effect on construction of copper(II) complexes with tridentate Schiff base ligand and DNA interaction

Two tridentate Schiff base ligands were synthesized by condensation of equimolar amounts of benzoylacetone and 2-amino-1-ethanol or 3-amino-1-propanol, H2L1 and H2L2, respectively. The reaction of the Schiff base ligands with Cu(CH3COO)2 in methanol leads to (CuL1)4, 1 and (CuL2)2, 2. In the tetranuclear cubane species, the tridentate H2L has both a chelating and a bridging mode, after double deprotonation of the enolic OH groups. The copper(II) centers are five-coordinate with a NO4 donor set from the ligands. The coordination geometry around each copper ion is essentially square pyramidal with one nitrogen and two oxygens from one ligand and two oxygens of adjacent ligands from the next unit of the cubane. In dinuclear 2, H2L2 has chelating and bridging modes after double deprotonation of the enolic OH groups. The dianionic form of the Schiff base coordinates forming a six-membered chelate ring with Cu(II). Two such monomeric CuL2 entities are eventually linked through the alkoxo bridges to produce dinuclear 2. The absorption spectra strongly suggest that 2 interacts with CT-DNA. Both 1 and 2 appear to be more efficient than the parent compound in DNA cleavage.

Halogenated metabolites isolated from Penicillium citreonigrum.

Three chromone analogs, 1-3, a chlorinated alkaloid sclerotioramine (4), together with two 11-noreremophilane-type sesquiterpenes with a conjugated enolic OH group and a brominated one, 5 and 6, respectively, were isolated from Penicillium citreonigrum (HQ738282). Compounds 1, 5, and 6 were new. Biological tests revealed that 4 exhibited a significant activity (IC50 7.32 μg/ml), and 6 showed a moderate activity (IC50 16.31 μg/ml) in vitro against HepG2 cell line, and 4 also displayed an activity comparable to that of acarbose against α-glucosidase.

Carbonic anhydrase inhibitors. Comparison of chlorthalidone, indapamide, trichloromethiazide, and furosemide X-ray crystal structures in adducts with isozyme II, when several water molecules make the difference

Thiazide and high ceiling diuretics were recently shown to inhibit all mammalian isoforms of carbonic anhydrase (CA, EC 4.2.1.1) with a very different profile as compared to classical inhibitors, such as acetazolamide, methazolamide, and ethoxzolamide. Some of these structurally related compounds have a very different behavior against the widespread isozyme CA II, with chlorthalidone, trichloromethiazide, and furosemide being efficient inhibitors against CA II ( K Is of 65–138 nM), whereas indapamide is a much weaker one ( K I of 2520 nM). Furthermore, some of these diuretics are quite efficient (low nanomolar) inhibitors of other isoforms, for example, chlorthalidone against hCA VB, VII, IX, and XIII; indapamide against CA VII, IX, XII, and XIII, trichloromethiazide against CA VII and IX, and furosemide against CA I and XIV. Examining the four X-ray crystal structures of their CA II adducts, we observed several (2–3) active site water molecules interacting with the chlorthalidone, trichloromethiazide, and furosemide scaffolds which may be responsible for this important difference of activity. Indeed, indapamide bound to CA II has no interactions with active site water molecules. Chlorthalidone bound within the CA II active site is in an enolic (lactimic) tautomeric form, with the enolic OH also participating in two strong hydrogen bonds with Asn67 and a water molecule. The newly evidenced binding modes of these diuretics may be exploited for designing better CA II inhibitors as well as compounds with selectivity/affinity for various isoforms with medicinal chemistry applications.

Reactions of methyl 4-hetaryl-2,4-dioxobutanoates with a mixture of aminoazole and aromatic (heteroaromatic) aldehyde

We previously described methods of synthesis of methyl 6-acyl-7-aryl-4,7-dihydrotetrazolo[1,5-a]pyrimidine-5-carboxylates and methyl 6-acyl-7-aryl-4,7dihydrotriazolo[1,5-a]pyrimidine-5-carboxylates by reactions of methyl acylpyruvates with a mixture of an aromatic aldehyde and 5-aminotetrazole [1] or 3-amino-1,2,4-triazole [2], respectively. With a view to further study how the structure of heterocyclic amine affects the direction of these reactions in the present work we examined reactions of methyl 4-(2-thienyl)and 4-(2-furyl)-2,4-dioxobutanoates with mixtures of aromatic (heteroaromatic) aldehydes and 5-amino-1methyltetrazole, 3,5-diamino-1,2,4-tetrazole, and ethyl 5-amino-1H-imidazole-4-carboxylate. By heating for a short time a mixture of methyl 4-(2-thienyl)or 4-(2-furyl)-2,4-dioxobutanoate, 5-amino-1-methyltetrazole, and thiophene-2-carbaldehyde, benzaldehyde, or pyridine-3-carbaldehyde in acetic acid we obtained the corresponding 5-aryl(hetaryl)-4-hetaroyl-3-hydroxy-1-(1-methyltetrazol-5yl)-2,5-dihydro-1H-pyrrol-2-ones Ia–Ic (Scheme 1). Compounds Ia–Ic are colorless or slightly colored crystalline substances, which are readily soluble in DMF and DMSO, soluble in ethanol and acetic acid on heating, and insoluble in water. They give rise to a positive color test (cherry color) with an alcoholic solution of FeCl3. The H NMR spectra of Ia–Ic contain signals from aromatic protons, hydroxy proton, CH proton in the 5-position of the pyrrole ring (δ 6.13–6.48 ppm), and protons in the methyl group (δ 4.27–4.33 ppm, s). In the IR spectra of Ia–Ic we observed absorption bands due to vibrations of the ketone carbonyl group (1607–1620 cm), lactam carbonyl group (1701– 1755 cm), and enol OH group (3250–3269 cm).

Derivatization of enolic OH of piroxicam: a comparative study on esters and sulfonates

A number of ester and sulfonate derivatives of piroxicam were prepared via acylation/sulfonation of the enolic OH of piroxicam. All the compounds were evaluated for their chemical stability and cyclooxygenase inhibiting properties. Data suggested that esters could be useful for the development of potential prodrugs. The sulfonate derivatives prepared for the first time were found to be stable. One of them showed a moderately selective COX-2 inhibition over COX-1 and would have lower gastrointestinal side effects than piroxicam due to the masked enolic OH group. A plausible mechanism for the acylation/sulfonation process has been proposed that involves participation of the pyridine moiety of piroxicam. Molecular structure of one of the ester was established for the first time by the crystal structure analysis from X-ray powder data.

Preparation and spectroscopic characterization of novel cyclodiphosph(V)azane of N1-2-pyrimidinylsulfanilamide complexes : Magnetic, thermal and biological activity studies

Hexachlorocyclophosph(V)azane of sulfadiazine, (sulfupyrimidine) [ N 1-2-pyrimidinylsulfanilamide] (H 2L 1), was prepared and reacted with sulfur and glycine to give (H 2L 2) and (H 2L 3) ligands, respectively. The prepared ligands; H 2L 1, H 2L 2 and H 2L 3, react in 1:2 [ligands]:[metal ions] molar ratio with transition metals to give coloured complexes in a relatively good yields. The complexes were characterized using different physicochemical techniques, namely elemental analyses, IR, UV–vis, mass, 1H NMR, molar conductance, magnetic, solid reflectance and thermal analysis. The spectral data reveal that all the ligands behave as neutral bidentate ligands and coordinated to the metal ions via pyrimidine-N and enolic sulfonamide OH. The molar conductance data reveal that the complexes are non-electrolytes while UV–vis, solid reflectance and magnetic moment data have been shown that the complexes have octahedral geometry. The thermal behaviour of the complexes is studied and the thermodynamic activation parameters are calculated. The ligands and their complexes show high to moderate bactericidal activity.

New Cyclodiphosph(V)azane Complexes of Fe(III), Co(II), Ni(II), Cu(II), Zn(II), and UO2 (II): Preparation, Characterization, and Biological Activity Studies

Hexachlorocyclodiphosph(V)azane of sulfamethoxazole, H2L, reacts with stoichiometric amounts of transition metal salts such as Fe(III), Co(II), Ni(II), Cu(II), Zn(II), and UO2(II) to afford coloured complexes in a moderate to high yield. The structure of the isolated complexes was suggested based on elemental analyses, IR, molar conductance, UV-Vis, 1H NMR, mass spectra, solid reflectance, magnetic susceptibility measurements, and thermogravimetric analysis (TGA). From the elemental analyses data, 1:2 (H2L:M) ratio is suggested and the complexes are found to have the general formula [(MX n )2(H2L)(H2O) m ] where M = Fe(III) (X = Cl, n = 3, m = 2), Co(II) (X = Cl, n = 2, m = 4), Ni(II) (X = Cl, n = 2, m = 4), Cu(II) (X = Cl, n = 2, m = 4), Zn(II) (X = Cl, n = 2, m = 4), and UO2(II) (X = NO3, n = 2, m = 0). The IR and 1H NMR spectral data revealed that H2L behaves as a neutral bidentate ligand coordinated to the metal ions through enolic sulfonamide OH and isoxazole N atoms. The UV-Vis, solid reflectance, and magnetic-moment data have shown that the ligands are coordinated to the metal ions in an octahedral manner. The molar conductance data show that the complexes are nonelectrolytes. The thermal data reveal that the coordinated water and anion molecules are lost in the first two steps while the ligand molecules are lost in the subsequent steps, leaving metal oxide residues. Different thermodynamic activation parameters are calculated using the Coats-Redfern equation. The prepared complexes showed high to moderate bactericidal activity compared with the ligand.

Structural investigations of isomeric oxidised forms of hyperforin by HPLC-NMR and HPLC-MSn.

The prenylated phloroglucinol hyperforin, thought to be an essential component for the anti-depressant activity of St. John's Wort (Hypericum perforatum), is unstable. The facile oxidative degradation of hyperforin poses serious problems for standardisation, and may also dramatically affect the pharmacological activity of the extracts. Hyperforin was dissolved in hexane and stored at room temperature for 3 days and yielded various closely related degradation products which, although difficult to isolate on the preparative scale, have been analysed by on-flow and stop-flow HPLC-NMR and HPLC-MS/MS. From on-line spectroscopic data, and with the aid of complementary in-mixture standard NMR two-dimensional correlation experiments, the different oxidised forms of hyperforin were found to be phloroglucinol derivatives in which a hydroxy-dihydrofuran ring is formed involving the enol OH at C-7 or C-9 (tautomeric form) and the prenyl chain at C-8 of the core nucleus of hyperforin. The strategy followed for the on-line identification of these constituents is discussed.

Antioxidant properties of galantamine hydrobromide.

The antioxidant properties of galantamine hydrobromide ((4alpha,6beta)-4a,5,9,10,11,12-hexahydro-3-methoxy-11-methyl-6H-benzofuro[3a,3,2-ef][2]benzazepin-6-ol hydrobromide) were studied in vitro, using luminol-dependent chemiluminescence and spectrophotometry. It was found that this compound was a scavenger of reactive oxygen species (ROS). By comparing the antioxidant effects of galantamine ((4alpha,6beta)-4a,5,9,10,11,12-hexahydro-3-methoxy-11-methyl-6H-benzofuro[3a,3,2-ef][2]benzazepin-6-ol), galantamine hydrobromide, narwedine (4a,5,9,10,11,12-hexahydro-3-methoxy-11-methyl-6H-benzofuro[3a,3,2-ef][2]benzazepin-6-one), and narwedine hydrobromide it was found that the antioxidant activity depended on the enolic OH group in the molecule. The presence of a quaternary nitrogen in the compound increased the strength of the scavenging effect. It is proposed that the antioxidant properties observed in vitro may contribute to the therapeutical effect of galantamine hydrobromide on patients with brain degeneration.

Hydrogen-Bonding in Cyclic 2-(3-Oxo-3-phenylpropyl)-Substituted 1,3-Diketones: 17O-NMR Spectra and X-Ray Structure Determination

Structures of cyclic 2-(3-oxo-3-phenylpropyl)-substituted 1,3-diketones 4a–c were determined by 17O-NMR spectroscopy and X-ray crystallography. In CDCl3 solution, compounds 4a–c form an eight-membered-ring with intramolecular H-bonding between the enolic OH and the carbonyl O(11)-atom of the phenylpropyl group, as demonstrated by increased shielding of specifically labeled 4a–c in the 17O-NMR spectra (Δδ(17O(11))=36 ppm). In solid state, intermolecular H-bonding was observed instead of intramolecular H-bonding, as evidenced by the X-ray crystal-structure analysis of compound 4b. Crystals of compound 4b at 293 K are monoclinic with a=11.7927 (12) A, b=13.6230 (14) A, c=9.8900 (10) A, β=107.192 (2)°, and the space group is P21/c with Z=4 (refinement to R=0.0557 on 2154 independent reflections).

Facile synthesis of 3‐spiroindolines

AbstractCyanoacetyldiazoindol‐2‐one (3), the condensation product of cyanoacetohydrazide with isatin (1), could be cyclized in acidic medium via its CN group and its enolic OH to give cyanomethyloxadiazole‐spiroindoline (4). The presence of the methylcyano side chain could be invested—through oximation, diazotization, or condensation with aldehydes—to form polyfunctional spiroindolines 5, 8–10. Also, a second route for preparing the title compound could be achieved through a nucleophilic attack on position 3 in the isatin derivatives, followed by subsequent ring closure to give 6 and 7. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:207–210, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10020

SYNTHESIS AND CHARACTERIZATION OF NEW Cu(II) COMPLEXES DERIVED FROM BENZILIC AND MANDELIC HYDRAZONES

Two new sets of Cu(II) complexes with newly synthesised benzilic and mandelic hydrazone derivatives were prepared in the mole ratios 1:1 and 1:2 (Cu:L). The structure of the complexes was identified on the basis of the data obtained from elemental and thermal analyses as well as IR, UV-visible, ESR spectra, and X-ray diffraction. The results indicate that the ligands are tightly bound to the metal ion through the phenolic OH oxygen, the azomethine nitrogen, and the enolic OH oxygen in case of the 1:1 complexes while for the 1:2 complexes the enolic OH group did not participate in bonding. The complexes have elongated octahedral as well as square-planar symmetries.

2,2′-Methylenebis(3-hydroxy-2-cyclohexen-1-one)

In the title compound, C13H16O4, the cyclo­hexene rings adopt a sofa conformation. Adjacent mol­ecules are connected by C—H⋯O intermolecular interactions. Each mol­ecule is characterized by O—H⋯O intramolecular hydrogen bonds. The anti arrangement of the enolic OH group and the carbonyl O atom in the solid state is similar to the anti arrangement of the NH and carbonyl groups in indigo.

Transacetylation of Ethyl α-Arylacetoacetates

A novel acetylating method using ethyl α-arylacetoacetates was established. Activation of β-keto esters by an aryl group made possible the quantitative transfer of the acetyl group from the keto ester to amines, EtOH and EtSH under mild conditions. The chemoselective acetylation of diamines and aminoalcohols was conducted.The introduction of an aryl group at the α-position caused various factors to act in concert with good effect, as follows : a) stabilization of the enol form, b) increased acidity of the enol OH group, c) protection of the acetyl group from attack of sterically hindered nucleophiles and d) promotion of the elimination of departing groups by electronic stabilization and steric repulsion.