Alkyl Phenylglyoxylates Research Articles

ChemInform Abstract: A Concise Diastereoselective Photochemical Synthesis of 3‐Hydroxyfuran‐2(3H)‐ones.

AbstractOxetanes (III) are obtained with high to moderate diastereoselectivity by photocycloaddition of alkyl phenylglyoxylates (II) to allylic alcohols (I).

A Concise Diastereoselective Photochemical Synthesis of 3‐Hydroxyfuran‐2(3H)‐ones

The photocycloaddition of alkyl phenylglyoxylates to allylic alcohols leads to oxetanes 3a–h with high to moderate (2R∗,4R∗)‐diastereoselectivity that can be easily ring‐opened to give 3‐hydroxyfuran‐2(3H)‐ones 4a–b.

Photodecarboxylative Additions of α-Thioalkyl-Substituted Carboxylates to Alkyl Phenylglyoxylates

Irradiations of alkyl phenylglyoxylates with sulfur-containing carboxylates yielded the corresponding photodecarboxylative addition products in moderate to good yields of 26-58%. Reductive photodimerization competed with decarboxylative addition in all cases. The reaction protocol was successfully transferred to a microreactor. With potassium 2-(methylsulfanyl)propionate, photoadditions gave diastereomeric mixtures with low selectivity for the like-isomer.

Analysis of the time-resolved FTIR spectra produced by the photolysis of alkyl phenylglyoxylates

The photochemistry of alkyl phenylglyoxylates (APG) was further investigated using time-resolved infrared spectroscopy. The primary focus was on the analysis of weak transient bands around 1828 and 1730 cm(-1) in the time-resolved FTIR spectra of glyoxylates. The observed transients were assigned to benzoyl and alkyl mandelate ester radicals, respectively. The formation of benzoyl radical was fast and attributed to the Norrish Type I process. In addition, the intensities of the strong FTIR bands around 1680 and 2100 cm(-1) were used to analyze the yields of the triplet state and ketene, respectively. These new and previous data on APG photochemistry are discussed in relation to the acrylate polymerization photoinitiation by alkyl phenylglyoxylates.

Observation of the two triplet state conformations of alkyl phenylglyoxylates.

Step-scan time-resolved FT-IR spectra of alkyl phenylglyoxylates in hexane with a 4 cm(-1) spectral resolution reveal splitting of the transient absorption signal near 1650 cm(-1) into two closely located peaks with different lifetimes on the nanosecond time scale. This signal had been previously assigned to the triplet state of the starting material that gives rise to the alpha-hydroxyphenylketene. In the current article, evidence is presented to assign these two peaks to different triplet state conformers only one of which undergoes fast Norrish Type II photoelimination. This assignment was made on the basis of chemical reactivity, steric effects, and kinetic data.

Application of Time-Resolved Step-Scan Fourier Transform Infrared Spectroscopy to Photochemical Mechanistic Investigations of Alkyl Phenylglyoxylates,

The photochemical reactivity of alkyl phenylglyoxylates has been investigated using time-resolved step-scan Fourier transform infrared spectroscopy. The time-resolved FTIR spectra of hexane solutions of methyl (MPG), ethyl (EPG), and isopropyl (iPPG) phenylglyoxylates and benzene solutions of MPG display two major transient absorption peaks in the carbonyl fundamental region around 1661 and 2105 cm-1. On the basis of the spectroscopic and kinetic evidence, the 1661 cm-1 transitions are assigned to the carbonyl fundamental of the triplet state of the corresponding alkyl phenylglyoxylate. The 2105 cm-1 band is attributed to the carbonyl stretch of α-hydroxyphenyl ketene, which is the postulated intermediate of the intramolecular hydrogen abstraction in alkyl phenylglyoxylates. These assignments are supported by the results of DFT calculations. From kinetic time profiles for the two observed transient infrared bands, the rate constants for the intra- and intermolecular γ-hydrogen abstraction were obtained an...

Observations of different triplet conformations in time-resolved infrared spectra of alkyl phenylglyoxylates.

Two different conformations of the triplet state of alkyl phenylglyoxylates were observed by means of time-resolved step-scan FT-IR spectroscopy. The amplitude of the peak corresponding to the sterically hindered conformation decreases as the size of the alkyl group increases. Both conformations exhibit similar reactivity in intermolecular hydrogen abstraction, but only one of them undergoes Norrish Type II photoelimination.

Mechanism of alkyl phenylglyoxylates photoreaction in the presence of oxygen

The rate of starting material disappearance for phenylglyoxylate esters possessing a reactive γ-hydrogen is not significantly influenced by the presence of oxygen. However, the products produced and their yields are quite different. A mechanism involving trapping of the 1,4-biradical intermediate by ground state oxygen following the triplet state γ-hydrogen abstraction is proposed. Rate constants for the various processes are deduced from literature values and from laser flash photolysis of the starting phenylglyoxylates.

Photochemical Reactions of Halo-/Aryl Sulfide-Substituted Alkyl Phenylglyoxylate, an Assessment of the Lifetime of the Intermediate 1,4-Biradical

Photochemical reactions of several halo/aryl sulfide-substituted alkyl phenylglyoxylates (1) were studied. For 2‘-bromo- (1b), 2‘-iodo- (1c), 2‘-(phenylthio)- (1d), and 2‘-(phenylsulfinyl)- (1e) ethyl phenylglyoxylate, vinyl phenylglyoxylate (2), proposed to be the result of β-elimination from the 1,4-biradical formed by triplet state γ-hydrogen abstraction, is the dominant photoproduct. In the cases 1b and 1d Norrish Type II products were also observed. Vinyl phenylglyoxylate (2) was not observed with 2‘-chloroethyl (1a), 3‘-bromopropyl (1f), and 3‘-(phenylthio)propyl (1g) phenylglyoxylate. The lifetime of the 1,4-biradical intermediate is deduced from the competition between the β-elimination of the monoradical and the normal biradical decay. The triplet lifetime and the photoreaction efficiency of 1 were not significantly affected by halogen-substitution.

ChemInform Abstract: Photochemical Reactions of Mercapto/Amino Substituted Alkyl Phenylglyoxylates Induced by Intramolecular Electron Transfer.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Rapid Regio‐ and Diastereoselective Paterno‐Buechi Reaction of Alkyl Phenylglyoxylates.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Photochemical reactions of sulfide-containing alkyl phenylglyoxylates

Abstract Ethylthioalkyl phenylglyoxylates (2) underwent regioselective photocyclization to produce up to 13-membered ring thiacyclols (3) in good yields. Cyclization occurred between the excited carbonyl group and the carbon a to the sulfur on the remote side. The more methylenes placed between the carbonyl group and the sulfide, the lower the yield of 3 while intermolecular hydrogen abstraction induced reductive dimerization and intramolecular Norrish Type II photolysis become competitive. The remote cyclization can be rationalized by a photoinduced electron transfer from the sulfur atom to the excited carbonyl group followed by proton transfer and subsequent cyclization of the resulting biradical. Rate constants for electron transfer increase as the chain connecting the electron donor and acceptor becomes longer and more flexible.

Rapid Regio- and Diastereoselective Paternò-Büchi Reaction of Alkyl Phenylglyoxylates.

Triplet excited states of alkyl phenylglyoxylates react rapidly (k = 9.4 x 10(9) M(-)(1) s(-)(1)) with electron rich alkenes forming oxetanes with high regio and stereoselectivity. The well-known intramolecular gamma-hydrogen abstraction (Norrish type II) cannot compete. When less electron-rich alkenes are used, the Norrish type II reaction becomes competitive. Intramolecular Paternò-Büchi reactions predominate in those alkyl phenylglyoxylates containing properly situated electron-rich alkene groups. The regioselectivity of this reaction is explained by the stability of the intermediate 1,4-biradical. The appropriate conformation at the instant of intersystem crossing determines the stereoselectivity of the products. The priority of the Paternò-Büchi over the Norrish type II reaction is understood by considering the conformation of phenylglyoxylate esters.

Photochemical reactions of mercapto/amino substituted alkyl phenylglyoxylates induced by intramolecular electron transfer

2′-Alkylthio ethyl phenylglyoxylates ( 1) and 2′-dimethylamino ethyl phenylglyoxylate ( 10) were synthesized and their photochemistry studied. In contrast to their oxygen analogs 3, which give normal Norrish type II cleavage products, the title compounds undergo intermolecular electron transfer from the heteroatom (sulfur/nitrogen) to the excited carbonyl group, followed by proton transfer and subsequent closing of the resulting biradicals to produce seven-membered ( 2)/five-membered ( 11) lactones in high yield. Thiadialkyl phenylglyoxylates ( 9) react inefficiently due to intramolecular self-quenching of phenylglyoxylate chromophores. The photoreactivity of α-oxothioester ( 14) was compared with that of its nitrogen (α-oxoamide) and oxygen (phenylglyoxylate) counterparts.

Alkyl phenylglyoxylates as radical photoinitiators creating negative photoimages1

S. Hu and Douglas C. Neckers, J. Mater. Chem., 1997, 7, 1737 DOI: 10.1039/A701797I