2-methyl-tetrahydrofuran oxygenate

The popular approach to tetrahydrofurans involves an electrophilic process and the commonly used electrophiles for the cyclization are acids, oxygen, halogen, mercury (see Section 3.11.2.2.9) and selenium. The ionic hydrogenation of furans with excess triethyl-silane in trifluoroacetic acid affords high yields, e.g. 2-methylfuran is reduced to 2-methyl-tetrahydrofuran and 2-ethylfuran to 2-ethyltetrahydrofuran (see Section 3.11.2.5). The synthesis of several dihydro and tetrahydrofurans containing natural products by chirality transfer from carbohydrates has been used successfully for total synthesis, e.g. (-)-nonactic acid. A reasonable yield of 2-alkyltetrahydrofuran was prepared from 4-alkylbut-l-en-4-ol by hydroboration followed by cyclization with p-toluenesulfonic acid. 

Levulinic Acid 2-Methyl-tetrahydrofuran Fuel additive (fuel oxygenates)... 

A solution of 50 g of 3 -acetoxy-16 -methyl-5a-pregnan-20-one in tetrahydrofuran (120 ml) is added over 5 to 10 min, the passage of oxygen being continued for a further 45 min while maintaining the temperature at... 

The oxidation of alcohols with lead tetraacetate was the first reaction used for oxygenation of an angular methyl group in steroids. It is a simple and efficient method and produces tetrahydrofuran derivatives directly from alcohols. 

Highly efficient C-H insertion adjacent to oxygen atoms to generate /9-hydroxy esters has been demonstrated [130, 143, 144]. Reactions with cyclic oxygenated systems have not been extensively explored with these carbenoids and only the reaction with tetrahy-drofuran has been reported [130]. The major sy -diastereomer 218 from the reaction of methyl phenyldiazoacetate with tetrahydrofuran at -50 °C was obtained in 67% yield with 97% enantiomeric excess (Eq. 29). 

Complex formation equilibria in binary mixtures of chloroform with dipropyl ether (PE), diisopropyl ether (IPE), methyl tert-butyl ether(MBE), tetrahydrofuran (THE), 1,4-dioxane (DOX), acetone (AC), and methyl acetate (MA) have been analyzed in detail. The complex formation equilibria in chloroform mixtures was compared to those previously examined for halothane (2-bromo-2-chloro-l,l,l-trifluoroethane) mixed with the same oxygenated solvents. It was found that the H-bonds formed by halothane are stronger than those formed by chloroform (Dohnal and Costas, 1996). 

Despite its unfavorable NMR properties, the nO nucleus has attracted considerable interest, since its chemical shifts represent a discriminating probe for structural and molecular properties. In a study of some 5-membered heterocycles (furan and isoxazole methyl derivatives) (840MR(22)55) it was found that the nO chemical shifts are mainly determined by the p-electron density on the oxygen atom. A nO downfield shift of 222 ppm is observed on the formal aromatization of tetrahydrofuran to furan (61HCA865). 

Tetrahydrofurans.1 Co(OAc)2 promotes a reaction between methyl acetoace-tate and terminal alkenes to form tetrahydrofurans. This reaction is similar to a synthesis of dihydrofurans effected with Mn(III) acetate (14, 198), but differs in that oxygen is required with the cobalt catalyst. Of further significance, only a single tetrahydrofiiran is formed and in relatively good yield (68-71 %). A dihydrofuran is also formed, but only in minor amounts. 

Mono-n-cyclopentadienylmagnesium compounds have so far only been isolated in the form of adducts with oxygen or nitrogen bases. The bis-(tetrahydrofuran) complexes of cyclopentadienyl(phenyl)- and -(methyl)-magnesium have been synthesized by Whitesides and co-workers (96) according to Eq. (4). 

Reductive cleavage of cyclic ethers This complex is effective for reductive cleavage of cyclic ethers. The order of reactivity is epoxide > oxetane > tetrahydrofurane>tetrahydropyrane>oxepane. It is less effective for cleavage of acyclic ethers, except for methyl ethers. The reaction involves formation of a complex of the ethereal oxygen with aluminum r-butoxide followed by Sn2 displacement with lithium triethylborohydride. Steric and electronic Victors are involved, but yields are >90% in favorable cases. 

The addition of tributylstannyllithium to the carbonyl group of various a-substituted aldehydes is accompanied by asymmetric a-induction8. The extent depends only on the relative sizes of a-substituents. The tributylstannyl anion exhibits much the same stereoselectivity as unhindered Grignard reagents (for 2,3-dimethylbutanal d.r. 3 1 and 2.5 1, respectively). Stereoselectivity is improved with aldehydes substituted at the /(-position by oxygen. For example, when a-methyl-/i-(benzyloxy)methoxypropanal is treated with tributylstannyllithium in tetrahydrofuran, a mixture of diastereomers is formed, the ratio of which varies from 5 1 at — 78°C to8 l at — 119"C8. 

When 2-methyl-2,5-pentaiiediot is treated with sulfuric acid, dehydration occurs and 2,2-dimethyl tetrahydrofuran is formed. Suggest a mechanism for this reaction. Which of the two oxygen atoms is most likely to be eliminated, and whv ... 

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