Tetramethylethylene oxidation

Despite the fact that singlet oxygen oxidizes tetramethylethylene (16) via the ene pathway, with abstraction of one of the 12 a protons, under electron-transfer photooxidation conditions dioxetane 32 (R = Me) has been generated [29]. The electron-deficient sensitizer 9-mesityl-10-methylacridinium ion (Acr+-Mes) in its excited state Acr"-Mes + was generated, in which the alkene radical cation and... 

Propylene oxide Tetramethylethylene oxide Heterocyclic Compounds, Oxygen, Furans Euran... 

One example of nucleophilic attack by a rr-electron system on a sulfur atom of a thiirane 1-oxide is shown in Scheme 51. S-Alkylthiirenium ions react with tetramethylethylene to transfer the S-alkyl group yielding the alkyne and an S-alkyl-2,2,3,3-tetramethylthiiranium ion (79MI50600). 

The presence of oxygen in the reaction mixture drastically changes the course of the reaction.(a3> Under these conditions acetone, carbon monoxide, carbon dioxide, and tetramethylethylene oxide are produced. Presumably tetramethylcyclopropanone is still produced as an initial product and the products observed result from oxygen addition to this species ... 

Ishikawa s endgame toward of 54 is shown in Scheme 3.12. First, the allylic alcohol function was oxidized by a substrate-directed dihydroxylation reaction, as developed by Donohoue and coworkers (66 % yield) [36]. This reaction is conducted using 1 equiv each of osmium tetroxide and tetramethylethylene diamine (TMEDA) and provides a method to obtain the syn-A i hydroxylation product in the... 

Tetramethyl glycol, b457 Tetramethylene oxide, t69 Tetramethylene sulfide, t87 Tetramethylethylene glycol, d569... 

Phenylthio-l-trimethylsilylalkanes are easily prepared by the alkylation of (phenylthioXtrimethylsilyl)mcthane as shown in Scheme 10 [40], The treatment of (phenylthio)(trimethylsilyl)methane with butyllithium/tetramethylethylene-diamine (TMEDA) in hexane followed by the addition of alkyl halides or epoxides produces alkylation products which can be oxidized electrochemically to yield the acetals. Since acetals are readily hydrolyzed to aldehydes, (phenylthioXtrimethylsilyl)methane provides a synthon of the formyl anion. This is an alternative to the oxidative transformation of a-thiosilanes to aldehydes via Sila-Pummerer rearrangement under application of MCPBA as oxidant [40, 41]. 

Amines such as diethylamine, morpholine, pyridine, and /V, /V, /V, /V -tetramethylethylene-diamine are used to solubilize the metal salt and increase the pH of the reaction system so as to lower the oxidation potential of the phenol reactant. The polymerization does not proceed if one uses an amine that forms an insoluble metal complex. Some copper-amine catalysts are inactivated by hydrolysis via the water formed as a by-product of polymerization. The presence of a desiccant such as anhydrous magnesium sulfate or 4-A molecular sieve in the reaction mixture prevents this inactivation. Polymerization is terminated by sweeping the reaction system with nitrogen and the catalyst is inactivated and removed by using an aqueous chelating agent. 

It is generally agreed that alkenyl hydroperoxides are primary products in the liquid-phase oxidation of olefins. Kamneva and Panfilova (8) believe the dimeric and trimeric dialkyl peroxides they obtained from the oxidation of cyclohexene at 35° to 40° to be secondary products resulting from cyclohexene hydroperoxide. But Van Sickle and co-workers (20) report that, The abstraction/addition ratio is nearly independent of temperature in oxidation of isobutylene and cycloheptene and of solvent changes in oxidations of cyclopentene, tetramethylethylene, and cyclooctene. They interpret these results to support a branching mechanism which gives rise to alkenyl hydroperoxide and polymeric dialkyl peroxide, both as primary oxidation products. This interpretation has been well accepted (7, 13). Brill s (4) and our results show that acyclic alkenyl hydroperoxides decompose extensively at temperatures above 100°C. to complicate the reaction kinetics and mechanistic interpretations. A simplified reaction scheme is outlined below. 

The method of photosensitized oxygenation was successfully applied in the preparation of alcohols 265-270 from sylvestrene (264),207 and seems to be the most simple and successful method for the preparation of optically active rose oxides (272,273) from (+)- or (—)-citronellol C271).177 It may also be used for the preparation of certain organo-metallic hydroperoxides. Thus, the triphenyl-tin derivative of tri-methylethylene (274) undergoes a photosensitized oxygenation reaction with a rate similar to that of tetramethylethylene, giving rise to the hydroperoxides 275 and 276 219... 

Oxidation of Tetramethylethylene. Tetramethylethylene, TME, was an excellent model olefin since it was rapidly and selectively oxidized in the presence of many transition metal complexes (12). Oxidation of TME in the presence of the group VIII metal complexes [MCI(CO)-(Ph3P)2] (M = Rh, Ir) at 50°C gave two major products 2,3-dimethyl-2,3-epoxybutane, I, and 2,3-dimethyl-3-hydroxy-l-butene, II (Reaction 5). Reaction mixtures were homogeneous with no observable deposits of insoluble materials. Little oxidation occurred under these conditions in the absence of the metal complexes, but low yields of I and II were obtained in the presence of a radical initiator (Table I). Reactions were severely inhibited by hydroquinone. The ruthenium (II) complex, [RuCl2(Ph3P)3]2, also promoted efficient oxidation of TME yielding I... 

Oxidation of organic substrates. This hydroperoxide converts 2,3-dimethyl-2-butcne into tetramethylethylene oxide with simultaneous formation of 3-bromo-4,5-dihydro-5-hydroxy-4,4-dimethyl-3,5-diphenyl-3H-pyrazole (2). Dialkyl olefins, however, are not epoxidized by I. Enol ethers are converted to a variety of epoxide rearrangement products.2... 

Work on the pyridine-modified ozonization of tetramethylethylene showed that pyridine oxide is not-a product of ozonization (8). Most of the pyridine (— 90% ) remains unchanged during double bond cleavage. Only one mole of acetone, rather than two, is formed for each mole of olefin oxidized. Other work with a disubstituted olefin, trans-4-octene, showed that ozonides are formed in the reaction so that the reaction of pyridine with ozonide to form acid and aldehyde cannot occur (9). An NMR study of trans-4-octene ozonolysis in the presence of pyridine using 1,2-dichloroethane as the solvent shows that aldehyde and hydroxyl-containing material (carboxylic acid, peracid, and other OH species) are formed directly during double bond cleavage. 

Suginome et al. have described a novel route to homotropones which involves the unprecedented oxidative rearrangement (18) — (19). The photoaddition of tetramethylethylene to the azaphenanthrene (20), giving (21), is likewise wholly unexpected and without precedent (Oberti et al.). 

Dienones of this class are useful starting materials for the preparation of bicyclic compounds via Diels-Alder reactions and for the synthesis of small ring compounds. The 2,4-dienone can be converted quantitatively to the 2,5-isomer by treatment with fuming sulfuric acid and subsequent hydrolysis. The oxidation procedure is also applicable to the conversion of mesity-lene to mesitol or of isodurene to isodurenol, and can be used to convert tetramethylethylene quantitatively and directly to pinacolone. ... 

In an attempt to determine the atmospheric oxidation processes that would result in an arene oxide functional group in PAHs, Murray and Kong (1994) studied the reaction of particle-bound PAHs with oxidants derived from the reactions of ozone with alkenes. Phenanthrene and pyrene were converted to arene oxides under these simulated atmospheric conditions. Control experiments indicated that the oxidant responsible for the transformation was not ozone, but a product of the reaction of ozone with tetramethylethylene (TME), probably the carbonyl oxide or the dioxirane derived from TME. 

Syntex workers7 later found that (3) can be dehydrogenated to (5) directly by DDQ in 90% yield (2.5 moles of DDQ, refluxing dioxane, 1-2 hrs.). This oxidation of an unactivated disubstituted olefin to a diene is rare a related reaction to the oxidation of tetramethylethylene to 2,3-dimethylbutadiene (2, 117). They then found that it was possible to shorten the original synthesis even further. Reaction of (1) with a modified Simmons-Smith reagent (this volume) gave (3) directly in 50% yield. The overall yield of (5) from naphthalene is thus about 40%. 

In addition to metal-yne n complexation, Pu and co-workers (522) synthesized and crystaUographically characterized a water soluble, metal-ene n-complex by reacting [Os(en)2H2H20] with a TMS-substituted enediyne (TMS=Tetramethylethylene). The X-ray structure shows q -enediyne complexation to osmium (Scheme 79), however, no metal-promoted Bergman cyclization reactivity is observed, and only enediyne dissociation occurs upon oxidation or photolysis of the metal complex. 

Reactions of cyclic nitronic esters are also described. 3-Nitro-isoxazoline-jV-oxide (32a) is itself a cyclic nitrone, and forms isoxazo lizidines (33a) when allowed to react with olefins (5) such as ethylene,112,129,130 vinyl acetate,129 propylene,129 and styrene.130 With tetramethylethylene, cyclopentene, and cyclohexene, the corresponding isoxazolizidines are also obtained.131... 

Recently Bartlett and Shimizu"3 demonstrated that triplet acetone derived from dioxetane lb chemisensitized the decomposition of benzoyl peroxide in carbon tetrachloride, affording chlorobenzene, which exhibited a photo-CINDP effect. Finally, we observed that the / -peroxylactone (60) afforded exclusively tetramethylethylene oxide when chemisensitized by lb, as shown in Eq. (46).116... 

The role of exciplexes in self-sensitized photo-oxidations has been further investigated by Stevens and co-workers.273 - Photoperoxidation of 1,3-diphenyl-isobenzofuran in solution proceeds at a rate which is independent of acceptor concentration when this is very low, and this observation has been interpreted in terms of a re-encounter of x02 and ground-state acceptor molecules generated in the same triplet-triplet annihilation act. This interpretation accounts for the failure of tetramethylethylene to inhibit the reaction completely. Processes 1—3 in Scheme 8 account for the observations if re-encounter effects are included,... 

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