Gary W. Griffin

Photo- and thermoinduced generation of 1,3-diaryl carbonyl ylides from 2,3-diaryloxiranes 1,3-dipolar cycloadditions to dipolarophiles

Abstract A group of symmetrically substituted 2,3-diaryloxiranes have been studied as photoprecursors for carbonyl ylides. The stereochemistry of the adducts obtained upon interception of these 4n pi-transient systems with a variety of dipolarophiles provides information on the mode(s) of electrocyclic opening of the oxiranes to carbonyl ylides, as well as the mechanism of the 4n + 2 cycloaddition process. The stereochemistry of the dipolarophiles is preserved in the cycloadducts, which is consistent with a concerted addition process; however, solvent effects, steric hindrance, and possibly secondary orbital overlap factors all may play a role in determining the product distribution.

Structural identification of p-dioxane-2-one as the major urinary metabolite of p-dioxane.

SummaryAnalysis by gas chromatography (GC) of the volatile compounds present in the urine from rats administered dioxane, a hepatic carcinogen to this species, revealed a major metabolite. The appearance of the metabolite was pH-dependent, undetectable at high pH; reacidification of the urine sample brought about the reappearance of the metabolite. The amount excreted was dose-dependent and time-dependent, reaching a maximum between 20 and 28 h after dioxane administration. Diethylene glycol administered to rats gave rise to the same metabolite. When isolated and purified from lyophilized urine by preparative GC, the metabolite exhibited an intense carbonyl band at 1750 cm−1 in the infrared spectrum. Nuclear magnetic resonance spectrum showed two triplets and one singlet with equal intensity at δ 3.85, 4.48 and 4.37, respectively. GC-mass spectrometric studies indicated a parent peak at m/e 102. The metabolite was identified as p-dioxane-2-one. Synthetic reference compound exhibited identical IR, NMR, and GC-mass spectra as the metabolite. The tentative pathway and the biological significance of dioxane metabolism are discussed.

Photoinduced generation of glucosyl cations from thioglycosides

Photochemically induced cleavage of thioaryl β-D-glucopyranosides using 1,4-dicyanonaphtalene as an electron-transfer agent, produces glycosyl cations potentially useful in glycosylation reactions.

Photosensitization via charge transfer or reversible electron transfer. Oxirane isomerization and sulfur dioxide extrusion

Abstract— N, N, N′ N′‐Tetramethylbenzidine (NTMB) photosensitizes the cis‐trans isomerization of stilbene oxiranes (SO) and the extrusion of SO2 from dibenzyl sulfone (DBS). In acetonitrile solution it is found that in the absence of SO or DBS, singlet NTMB undergoes three processes: intersystem crossing to triplet NTMB (φISC= 0.63, kISC= 6.3 × 107s‐1), fluorescence (φf= 0.30, kf= 3 × 107s‐1), and formation of a cation by electron ejection (φion= 0.09). Both singlet and triplet sensitization are observed. A charge transfer or reversible electron transfer mechanism is proposed to explain the results.

Transient spectral and kinetic behaviors of carbonyl ylide photogenerated from 2,2-dicyano-3-(2-naphthyl)-oxirane

Abstract On laser flash photolysis, by direct light absorption as well as under energy transfer sensitization by aromatic ketone triplets, 2,2-dicyano-3-(2-naphthyl)oxirane in fluid solutions forms an ylide characterized by broad and intense absorption spectra (λmax = 610 nm, ϵmax = 2.0 × 104 M−1 cm−1 in benzene) and unusually long lifetimes in aprotic solvents (τY = 130 μs in benzene). The ylide reacts with water, alcohols and dipolarophiles with rate constants that are atypically low (103 – 106 M−1 s−1). The reactivity follows a trend parallel to that of acidity of alcohols and opposite to that of electron-rich character of dipolarophiles.

Photoinduced electron-transfer reactions of aryl glycosides☆

Abstract The photolytic effects of ultraviolet, as well as other electromagnetic, radiation on carbohydrates are of interest in connection with photodegradation of cellulose and potential application in the photolytic cleavage of lignocellulosic bonds. Aryl glycosides, model compounds for lignocellulosic systems, were irradiated under conditions selected to achieve photoinduced electron-transfer. Various anomeric phenyl d -gluco- and d -galacto-pyranoside solutions in acetonitrile saturated with oxygen, air, or nitrogen and containing 1,4-dicyanonaphthalene (DCN) were irradiated at 350 nm for extended periods, and cleavage of the radical cation formed upon electron transfer to give the simple monosaccharide and phenol was observed. In the presence of methanol, it is possible to intercept the cationic intermediate, with formation of the correspondingmethyl glycosides. Control experiments conducted in the presence of oxygen, air, or nitrogen in the absence of DCN showed little or no conversion. Comparison of the modes of fragmentation in solution with those observed in the gas phase upon electron impact in the mass spectrometer was made, and mechanisms for the reactions induced by electron transfer under these conditions are proposed.

Cycloelimination reactions of cyclic aryl pinacol sulfites and carbonates via photosensitized reversible electron transfer

Abstract Evidence is presented that the singlet and triplet photosensitized cycloelimination reactions of cyclic aryl pinacol sulfites and carbonates proceed by reversible electron transfer and yield products which are different from those formed on direct photolysis.

Enhancement of toxicity and enzyme-repressing activity ofp-dioxane by chlorination: Stereoselective effects

The acute toxicity of p-dioxane may be enhanced up to 1000-fold by chlorination of the compound. The effect was stereoselective. Of the stereoisomers tested, tetrachloro-p-dioxane, isomer I (2r, 3t, 5t, 6c) was over 80 times more toxic than isomer II (2r, 3c, 5t, 6t). The latter compound was also a potent repressor of hepatic dimethylnitrosamine-demethylase I (DMN-d) and aryl hydrocarbon hydroxylase (AHH).

The sensitized photooxygenation of methyl substituted 1,2-diphenylcyclobutenes

Abstract A series of Me substituted 1,2-diphenylcyclobutenes was subjected to dye-sensitized photooxidanon in the presence ofmethylene blue. In the case of the 3,3-dimcthyl-, 3,3,4-tnmethyl- and 3,3,4,4tetramcthyl, 2-diphcnylcyclobutencs, the sensitized oxidations arc accompanied by ring-contraction with concomitant ortho hydroxylation of one aromatic nucleus. When electron transfer induced photooxidation techniques utilizing 9,10-dicyanoanthraccne (DCA) as a sensitizer are employed with the series of Me substituted diphcnykyclobutenes, the reactions take a markedly different course and a broad spectrum of oxidation products are obtained including, most notably, ozonides of the cyclobutencs. The mechanisms of these conversions are addressed and the significance of the results discussed.

Oxopyrazoline-spiro-oxirans. A new class of reactive heterocycles

Chemical and spectral properties of a series of 1-oxa-5,6-diazaspiro[2.4]hept-6-en-4-ones, synthesized by the oxidation of 4-alkylidene- or 4-arylidene-1-aryl-2-pyrazolin-5-ones are reported.