Syntheses and rearrangements of ketene mercaptals derived from some active methylene compounds and carbon disulphide

By use of the ion pair extraction technique, tetrabutylammonium salts of diethyl malonate, methyl cyanoacetate or malodinitrile were reacted with carbon disulphide giving salts of dithioacids (or of the tautomeric gem-mercapto thiolates) and of ketene mercaptals. Ketene methyl allyl mercaptals derived from diethyl malonate or methyl cyanoacetate rearranged at room temp to dithioesters by S → C allyl migration. The corresponding methyl crotyl derivatives gave equilibrium mixtures of the ketene mercaptals and the dithioesters, each of which were shown to undergo S → C and C → S rearrangements, respectively, with inversion of the crotyl group. Contrary to this the ketene dicrotyl mercaptals rearranged during distillation (at about 150°) with retention of the crotyl group. Methyl [(methylthio, crotylthio)methylene] cyanoacetate underwent fragmentation at 170° to MeSSMe, MeScrotyl, MeS(1-methylallyl) and the “desaurin”: 2,4-bis-(carbomethoxy-cyan-methylen)-1,3-dithiocyclobutan. Similarly bis(allylthio)methylene malodinitrile yielded diallyl sulphide.     

Photodecomposition of polymethylsiloxane

Infrared spectroscopy studies were undertaken to determine the effects of ultraviolet light radiation on a methylsiloxane resin. The results indicate that SiCH₂Si linkages were formed as a result of irradiation at wavelengths above 281 mμ from a xenon are lamp; on the other hand, Si? OH and SiCH₂CH₂Si linkages were formed instead when the resin was exposed to the lower wavelengths emitted from a mercury vapor lamp. The different effects on the resin induced by the two ultraviolet light sources are attributed to the fact that only the energies from the mercury vapor lamp radiation are sufficient to cause the excitation of oxygen molecules in the air surrounding the irradiated polymer. The excited oxygen molecules prevented the formation of SiCH₂Si structures by interacting with active %tbond;Si units that were formed as a result of Si? C bond rupture to produce Si? OH; SiCH₂CH₂Si linkages were formed as the result of a secondary reaction.     

由2-(1, 3-亚丙二硫基)亚甲基脂环酮出发合成共轭的烯酮硫缩醛

2-(1, 3-亚丙二硫基)亚甲基脂环酮(2')与甲基、丁基、仲丁基Grignard试剂经1, 2-加成反应得产物3, 3在酸的催化下脱水生成共轭的烯酮硫缩醛类化合物4。本实验提供了一条经由α-羰基烯酮环二硫代缩醛类化合物合成在有机合成中有重要应用的共轭烯酮硫缩醛类化合物的新途径。     

Photodecomposition of selenosulfonates and their facile photoaddition to alkenes 1

Phenyl areneselenosulfonates ($\text{1}$) are very photosensitive and easily undergo photodecomposition via initial homolysis of the SeS bond. In the presence alkenes this facile photodissociation of $\text{1}$ can be used to initiate a free radical chain reaction (eq 6) that leads to addition of $\text{1}$ to the alkene to form β-phenylselenosulfones ($\text{2}$). The photoaddition requires much shorter reaction times than the non-photolytic addition of $\text{1}$ to alkenes described recently.²     

Electrophilic addition of 2-chloropolyfluoroalkylsulfenyl chlorides to ketene

Conclusions The reaction of 2-chloropolyfluoroalkylsulfenyl chlorides with ketene gives 2-chloropolyfluoroalkylthioacetyl chlorides.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2358–2360, October, 1987.     

Breaking of ketene bonds during HCl addition to trimethylsilylketene

IR spectroscopy is coupled with the matrix isolation technique to study the reaction of trimethylsilylketene with HCl. From 50 K trimethylsilylketene reacts with hydrogen chloride, leading to the cleavage of the Si-C bond and the formation of trimethylsilyl chloride and acetyl chloride, through intermediate trimethylsilylacetyl chloride which was identified. A reaction profile for this result is proposed based on a theoretical study carried out at the DFT level.     

Phenyl(trimethylsilyl)ketene. Some ketene reactions with diazomethane

Phenyl(trimethylsilyl)ketene was prepared by the zinc dehalogenation of phenyl(trimethylsilyl)bromoacetyl chloride. This ketene parallels tirmethylsilylketene in stabibility and lack of reactivity in cycloaddition reactions. The reaction of phenyl(ethyl)-, phenyl(trimethylsilyl)- and trimethylsilylketenes with diazomethane at ?78°C is described. Only the $\text{2}\text{1}$ cycloadducts, the cyclobutanones, could be isolated.     

Cycloaddition of nitrile N-oxides to bis(trifluoromethyl)ketene

Conclusions The cycloaddition of nitrile N-oxides to bis(trifluoromethyl)ketene leads to 2-hexafluoroisopropylidene-1,3,4-dioxazoles.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2140–2142, September, 1970.     

Addition of nucleophilic reagents to bis(trifluoromethyl) ketene

Conclusions When -hydrohexafluorothiolisobutyric acid is reacted with bis (trifluoromethyl) ketene, the initial act is addition bo the C=O multiple bond of the latter.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2408–2410, October, 1982.     

Fluoroketenes IX. Functionality α to the ketene group

Three new fluoroketenes have been prepared having the acid fluoride, sulfonyl fluoride and ester functions, respectively, α to the ketene group. The synthesis and characterization of these ketenes is described, along with a convenient synthesis of trifluoromethylmalonyl fluoride.     

Acetylation of oxazolidines with ketene

For the first time oxazolidines are acetylated with ketene, at the nitrogen atom, to give a number of hitherto unknown N-acetyloxazolidines.     

Highly enantioselective oxidations of ketene dithioacetals leading to trans bis-sulfoxides

Ketene dithioacetals undergo a Sharpless-type asymmetric oxidation using (+)-DET, Ti(O(i)()Pr)(4), and cumene hydroperoxide to give the trans bis-sulfoxides 4a-f with essentially complete control of enantioselectivity and diastereoselectivity. The high enantioselectivity is a consequence of carrying out two asymmetric processes on the same substrate. However, this should lead to the formation of a small amount of the meso isomer but none was isolated. From monitoring the enantioselectivity of the monoxide over time, it was concluded that small amounts of the meso isomer must be formed. The inability to isolate this compound could be because it acted as a ligand on titanium and remained tightly bound even upon workup.     

Cationic polymerization of dimethyl ketene

By ionic polymerization, dimethyl ketene can lead to polyketone, polyester or polyacetal. In the presence of AlBr₃ as Lewis acid initiator, pure polyketone can be obtained in nitrobenzene/carbon tetrachloride (50/50, v/v). With other cationic initiators or solvents, a mixture of polyketone and polyester was characterized. According to experimental conditions, a cyclic trimer was also observed by backbiting reaction, a cyclic dimer by heating to room temperature and a cyclic lactone when acetone was used as solvent. ¹³C n.m.r. is the most effective technique to determine polyketone purity. For example, an important modification of f.t.i.r. spectrum was noticed after melting and crystallization of the polymer with appearance of new bands which could correspond to polyester or polyacetal bands regarding to literature data. In fact, these bands correspond to change in morphology and ¹³C n.m.r. spectrum shows no structure modification. Polyketone degradation occurs at about 340 °C and the polymer is stable for several hours at 205 °C.     

Photodecomposition of poly(styrene peroxide)

Photodecomposition of poly(styrene peroxide) (PSP) has been carried out in detail by irradiating (300-360 nm) the PSP solution in CHCl₃ and the products were analyzed by gas chromatography-mass spectrometry (GC-MS) method. In addition to benzaldehyde, α-hydroxy acetophenone and phenyl glycol reported in earlier studies, two new products, viz., α-methoxy acetophenone and α-benzyloxy acetophenone were also observed, the mechanism of their formation discussed. The plausible reasons for the higher percentage of disproportionation products in PSP photolysis compared to that reported in its thermolysis are also discussed.     

Structure and Medium-Dependent Photodecomposition of Fluoroquinolone Antibiotics

The photochemical reactivity of four fluoroquinolone antibiotics is examined. For norfloxacin (NOR), enoxacin (ENX) and lomefloxacin (LOM), the only process occurring is defluorination (from position 6 for the first two drugs, from position 8 for the last one). The quantum efficiency is both structure and medium dependent (4 close to 0.5 both in water and in 0.1 M phosphate buffer for LOM,- 0.01 for ENX and 0.004 for NOR in buffer, but more than an order of magnitude higher in neat water). Ofloxacin (OFL) is less light sensitive φ 0.001) and undergoes, in part, reactions different from defluorination. The photoreaction involves heterolytic C-F bond fragmentation and its efficiency is determined by the internal charge-transfer character of the excited state (increasing in the series OFL < NOR < ENX < LOM according to the electronegativity of the substituent in position 8) and by the stabilization of the resulting aryl cation (larger for the 8-cation than for the 6-cation). The relevance of these data for the rationalization of the known phototoxicity of these drugs is discussed.     

Cyclic dithio-carbenium ion salts and their conversion to ketene dithioacetals

1,2-Ethanedithiol and 1,3-propanedithiol were treated with perchloric acid in acetic anhydride to give 2-methyl-1,3-dithiolan-2-yl and 2-methyl-1,3-dithian-2-yl perchlorates, respectively, which were converted to ketene dithioacetals by deprotonation with tertiary amines.     

Electronic states of ketene radical cation

The doublet electronic states of ketene, and ketene-d₂, radical cations produced by photoionisation with Helα (58.4 nm) and Hellα (30.4 nm) radiation, were studied by photoelectron spectroscopy. Seven such states were found below 28 eV ionisation energy and were assigned by comparison with the ionisation energies calculated by the correlated PNO-CEPA approach. The agreement is within ≈ 0.3 eV of the experimental data. An analysis of the contributions of reorganisation and correlation effects to the calculated ionisation energies is presented. The vibrational frequencies exciteα in four of the states of ketene-d₂ and ketene are presented and discussed in view of the assignments.