Saturated cyclic ethers

Fragmentation Losses from the molecular ions are 1, 29, and 30 Daltons with the loss of 29 (CHO) being characteristic of cyclic ethers. This loss also appears in the mass spectra of unsaturated cyclic ethers, such as furans and benzofurans. The fragmentation of saturated cyclic ethers generally shows a M — 1 ion. 

The reagent has been used to chlorinate certain saturated cyclic ethers.2 Thus tetrahydrofurane gives frans-2,3-dichlorotetrahydrofurane as the major product (26% yield). 

USE Solvent for fats, waxes, resins. In organic synthesis Undergoes the reactions of a primary alcohol, while the ring exhibits characteristics of a saturated cyclic ether. Caution Moderately irritating to skin, mucous membranes. 

Reaction of ammonia or amines with saturated cyclic ethers containing five or six ring members causes the ether oxygen atom to be replaced by an NH or NR group, but the conditions needed are so drastic that this is rarely of interest for laboratory practice. 

Saturated cyclic ethers are inert like acyclic ethers, requiring strong conditions for C-O bond cleavage this contrasts with heterocycles having smaller ring sizes (sections 27.2 and 27.3). 

One-carbon homologations of unusual types are illustrated by the conversion of an oxiran into an oxetan (Scheme 6) through the use of a-lithioalkyl selenides, a method which can, in principle, involve higher members of the saturated cyclic ether series. Further examples of uses of cr-lithioalkyl selenides have been described ... 

The reductive cleavage of saturated cyclic ethers by aluminium turnings with a HgCl2-ZnCla-MeI catalyst in THF gives alkoxyalane polymers such as (17). The organic synthetic uses of these polymers has been discussed. ... 

The reaction described is of considerable general utility for the preparation of benzoyloxy derivatives of unsaturated hydrocarbons.2"8 Reactions of 2-butyl perbenzoate with various other classes of compounds in the presence of catalytic amounts of copper ions produce benzoyloxy derivatives. Thus this reaction can also be used to effect one-step oxidation of saturated hydrocarbons,9, 10 esters,6,11 dialkyl and aryl alkyl ethers,12 14 benzylic ethers,11,15 cyclic ethers,13,16 straight-chain and benzylic sulfides,12, 17-19 cyclic sulfides,11,19 amides,11 and certain organo-silicon compounds.20... 

Saturated alkane-1,2-carboxylic acids and alkane-1,3-carboxylic acids give, in general, three types of products bis(trifluoromethyl)alkancs, cyclic a,a,a, a -tetrafluoro ethers and linear bis(pentafluoroalkyl) ethers. The 1,2-dicarboxylic acids, succinic and halosuccinic acids, give as the main products the cyclic ethers 6, derivatives of tetrahydrofuran, in ca. 30-50% yield, but from 1,3-dicarboxylic acids the yields of the corresponding six-membered ethers 9 are 16%.118... 

The two substituents on the /3-lactam can be longer and either saturated or unsaturated alkyl groups. The bromo alcohol 259 undergoes cyclization in the presence of base (triethylamine was found to give the best result) to yield the cyclic ether 260 <2005PAC2061>. The unsaturated diiodide 261 yields 262 upon reaction with sodium sulfide <1995TL7913>. 

Pentacene ethers 37-39 (Fig. 3.8) were prepared in an attempt to reduce the HOMO energy level relative to functionalized pentacene 29 [52]. These cyclic ether compounds were surprisingly stable, soluble and easily crystallized. Saturated diox-ane compound 37 has an oxidation potential of 0.580 V vs SCE (similar to that of unfunctionalized pentacene), but the axial hydrogen atoms on the dioxane ring prevent -stacking interactions in the crystal. Derivatives 38 and 39 were synthesized to overcome this structural issue. Although the change of oxidation potential... 

Low permittivity electron donor solvents saturated cyclic and linear ethers which are good Lewis bases but have dielectric constants less than about 10. 

The saturated five-membered cyclic ether resembles furan but has four additional hydrogen atoms. Therefore, it is called tetrahydrofuran (THF). One of the most polar ethers, tetrahydrofuran is an excellent nonhydroxylic organic solvent for polar reagents. Grignard reactions sometimes succeed in THF even when they fail in diethyl ether. 

Pyrans (Oxanes) The six-membered cyclic ethers are commonly named as derivatives of pyran, an unsaturated ether. The saturated compound has four more hydrogen atoms, so it is called tetrahydropyran (THP). The systematic term oxane is also used for a six-membered ring containing an oxygen atom. 

Over Raney Ni at 200-250°C, however, the main reactions of the dihydrocoumarin formed were saturation of the benzenoid ring to give octahydrocoumarin (3) and its conversion to the cyclic ether, hexahydrochroman (4), although polymeric products were also formed in 6-27% yields. The hydrogenation pathways and the products of coumarin and related compounds over copper-chromium oxide and Raney Ni are summarized in Scheme 10.4. For the formation of the cyclic ether 4 over Raney Ni,... 

In the photoaddition of a saturated hydrocarbon to ethyl propiolate (equation 19) it is likely that the excited state of the acetylenic ester initiates reaction by abstracting a hydrogen atom from the hydrocarbon. The addition of cyclic ethers to an alkyne seems similar (equation 20), although a ketone sensitizer is required for addition of tetrahydropyran or dioxan . When reactions of this type involve a conjugated acetylenic ester, the first-formed a,p-unsaturated ester can normally undergo further photochemical reaction to produce the p,y isomer (see equations 19 and 20). 

A transition metal catalyzed synthesis of ethers by carbene insertion into the O—bond has been reported. Not only saturated but also unsaturated alcohols can be utilized in this catalytic process. ° Intermolecular and intramolecular oxirane ring opening reactions by alkoxides and phenoxides also provide efficient and stereospecific preparations of acyclic and cyclic ethers. The procedures have been surveyed in detail. ... 

The first ultraviolet band of saturated ethers begins around 200 nm (e.g., cyclic ethers except ethylene oxide), or slightly below (e.g., open-chain ethers and ethylene oxide). It often shows structure and tends to be more Intense than the first band the alcohols, with which it shares assignment to an... 

Catalytic hydrogenation of dihydrothebaine methine [ix] with colloidal palladium in dilute acetic acid causes saturation of the 9 10 double bond, scission of the cyclic ether, and hydrolysis of the enol ether group giving dihydrothebainone dihydromethine [xvm] [3], and this is the most satisfactory method of preparing the latter. The dihydromethine [x] may be reduced to [xvm] under the same conditions [3]. [xvm] can also be prepared by hydrolysis of dihydrothebaine dihydromethine [x] to dihydrocodeinone dihydromethine [xix] (also accessible by the chromic acid oxidation of a-tetrahydrocodeimethine [xx] [3]) followed by aluminium amalgam reduction [3]. 

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