Methyltetrahydrofurans, oxidation

The reactions can also be effected by phenyliodonium diacetate.377 A mechanistic prototype can be found in the conversion of pentanol to 2-methyltetrahydrofuran. The secondary radical is most likely captured by iodine or oxidized to the carbocation prior to cyclization.378... 

We have studied the anodic oxidation of unsaturated alcohols using the controlled potential electrolysis (E = 1.9V vs SCE) in CH3CN-O.I mol/1 Et4NC104 solution in a divided cell [110]. The oxidation of 4-pentenol after consumption of 0.8 F/mol gave 2-methyltetrahydrofuran and tetrahydropyran as the major products. The oxidation of 5-pentenol gave 2-methyltetrahydro-pyran and oxepam, while the oxidation of 3-butenol under the same reaction conditions did not give the cyclic products. We rationalized this reaction as the electrongenerated acid (EGA) catalyzed intramolecular cyclization (Scheme 44). 

LDH-WC>4 has also been applied for oxidative bromination of unsaturated hydrocarbons (367). In a first step, W on LDH catalyzes the oxidation of Br with H202. Subsequently, the resultant bromonium species (Br+, which could be equilibrated with species such as HOBr or Br2) react rapidly with the target molecules. An advantage of the oxidative electrophilic bromination is that the active bromine is formed in situ in a controlled way there is no direct contact with Br2. Moreover, the bromination is performed under mild conditions such as room temperature, atmospheric pressure, and near neutral pH. Indeed, the FI ) 11-WO -catalyzed bromination mimics the enzymatic activity of bromoperoxidases not only formally but also organizationally and mechanistically. For example, indene is bromohydroxylated almost quantitatively with NH4Br and H2O2 in a water-2-methyltetrahydrofuran solvent mixture (368) ... 

Fig. 21. The variation with surface of the initial percentage yield of major products from the oxidation of n-pentane. Initial temperature = 290 °C initial pressure of n-pentane = 25 torr initial pressure of oxygen = 12.5 torr total pressure = 82 torr volume of reaction vessel = 500 cm. , pent-2-ene o, 2-methyltetrahydrofuran e, acetone , pent-l-ene e, butanone. (From ref. 106.)...

NMR speetroseopie studies of Li- N labeled lithium hexamethyldisilazide in solvents ineluding THF, 2-methyltetrahydrofuran (2-MeTHF), 2,2-dimethyltetrahydrofuran (2,2-Me2THF), diethyl ether (Et20), t-butyl methyl ether (Bu OMe), n-butyl methyl ether (Bu OMe), tetra-hydropyran (THP), methyl i-propyl ether (Pr OMe), and trimethylene oxide (oxetane) have been used to eharaeterize the nature of the solvated speeies. Mono-, di-, and mixed-solvated dimers ean be identified in the limit of slow solvent exehange, but ligand exehange is too fast to observe... 

Biaryl synthesis 3 Diaryl highcr-ordcr cuprates can undergo oxidative coupling in 2-methyltetrahydrofuran to form unsymmetrical biaryls in good yields. 

Oxidation of 2-methyltetrahydrofuran gives two hydroperoxides, 2-methyl-2-hydroperoxy and 2-methyl-5-hydroperoxyhydroperoxide, in a ratio of 3 2 [292], The decomposition products of these hydroperoxides are 7-butyrolactone, 7-methyl y-butyrolactone, 7-acetopropanol and rc-propyl acetate. Two hydroperoxides are formed in the oxidation of 2,5-dimethyltetrahydrofuran, a mono- and a dihydroperoxide [203]. 

Oxidation of the precursor hydrazones to the corresponding diazo compounds 10 and 12 can be carried out with active Mn02 but not with yellow HgO [8]. When photolyzed in 2-methyltetrahydrofuran (MTHF) glass at 10 K, they show EPR fine structures characteristic of unoriented triplet species. The zero-field splitting (zfs) parameter D/hc of a carbene is governed by the dipolar interaction between the unpaired electrons in the a- and n-orbitals at the carbenic center. The smaller D/hc value of thep isomer 11 than that of the m isomer 13 shows the extended delocalization of the n-spin in the former. The corresponding value diminishes further in the p-substituted 1,3-butadiyne 21 [8]. 

Photochemical reactions of nitroso oxides at low temperatures with stilbenes have been reported [35]. Several singlet nitroso oxides were generated by the thermal reaction of triplet nitrenes with triplet oxygen at 95 K in 2-methyltetrahydrofuran. After photolysis of the nitroso oxides at 77 K, the formation of intermediates was observed. From spectroscopic and kinetics data, the authors postulated the formation... 

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