Diols ethers, cyclic

The reaction of a, to-diols or cyclic ethers with a stoichiometric amount of BTMA Br3 in carbon tetrachloride, or in acetic acid in the presence of aqueous Na2HP04 or CH3COONa, at 60-70°C gave lactones. The results are shown in Figure 22. 

Fig. 22. Lactonization of a, co-diols and cyclic ethers with BTMA Br3...

Robinson, P.L., Barry, C.N., Kelly, J.W., and Evans, S.A., Diethoxytriphe-nylphosphorane a mild, regioselective cyclodehydrating reagent for conversion of diols to cyclic ethers. Stereochemistry, synthetic utility, and scope, /. Am. Chem. Soc., 107, 5210, 1985. 

Halogens are frequently used as oxidation agents and, under two-phase conditions, they can either be employed as ammonium complex halide salts [3], or in the molecular state with or without an added quaternary ammonium catalyst [4]. Stoichiometric amounts of tetra-n-butylammonium tribromide under pH controlled conditions oxidize primary alcohols and low-molecular-weight alkyl ethers to esters, a,cyclic ethers produce lactones [3], and secondary alcohols yield ketones. Benzoins are oxidized to the corresponding benzils (80-90%) by the tribromide salts in acetonitrile in the presence of benzoyl peroxide [5]. 

Dehydration of diols to cyclic ethers. The reagent dehydrates a variety of diols to cyclic ethers with formation of triphenylphosphine oxide as the co-product. Yields of cyclic ethers are high from 1,2-, 1,4- and 1,5-diols. Although (Z)-2-butene-1,4-diol is converted into 2,5-dihydrofuran in 95% yield, the (E)-isomer is converted in 35-40% yield into 3,4-epoxy-l-butene.1... 

A range of diols and cyclic ethers were used to carry out alkylation of aromatics (benzene, toluene, xylenes, trimethylbenzenes, naphthalene) in the presence of triflic acid.204 310 In a recent study,311 various methyl-substituted benzene derivatives were alkylated with 1,4-diols [Eq. (5.117)] to form substituted tetralin derivatives in high yields. The transformations involve an intermolecular alkylation step followed by intramolecular alkylation (cyclialkylation). 2,2,5,5-Tetramethyltetrahydrofuran is similarly effective. For example, it alkylates benzene to give octamethyloctahydroan-thracene (98% yield) and reacts with naphthalene to yield octamethyloctahydrote-tracene [Eq. (5.118)]. 

Another possible side reaction under experimental polyesterification conditions is the dehydration of a-diols (Eq. 2.19, Table 2.4). It changes the structure of some constitutional units. Depending on the diol used, cyclic ethers and aldehydes can also be formed. 

The scope and synthetic utility of dioxyphosphoranes, and particularly, diethoxytriphenylphosphorane (DTPP), as useful cy-clodehydrating "reagents" for the conversion of diols to cyclic ethers have received only superficial attention (1). The DTPP-diol - ether route has several unique advantages over existing methods (a) the reaction conditions are effectively neutral and mild, (b) the stereoselectivity in the closure of both unsymmet-rical and symmetrical diols to cyclic ethers is high, and (c) the isolation of the product(s) from triphenylphosphine oxide (TPPO) is convenient. 

We have systematically examined the facility with which DTPP promotes the cyclodehydration of simple diols to cyclic ethers 1,3-propanediol (1) - oxetane (2) (2-5%) 1,4-butanediol (3) te-trahydrofuran (4) (85%) 1,5-pentanediol (5) - tetrahydropyran (6) (72%) 1,6-hexanediol (7) - oxepane (8) (55-68%). Increased alkyl substitution at the carbinol carbon s gnificantly diminishes the facility for cyclic ether formation. For example, a mixture of meso- and d, 1 —2, 6-heptanediol gave only 6-10% of the cis- and trans-2,6-dimethyltetrahydropyrans when treated with DTPP. While diol 1 resists cyclodehydration with DTPP to oxetane, some 2,2-di-substituted 1,3-propanediols are readily converted to the appropriate oxetanes [e.g., 2-ethyl-2-phenyl-l,3-propanediol -> 3-ethyl-3-phenyloxetane (78%)]. 

Stereochemical information on the mode of cyclodehydration of unsymmetrical diols to cyclic ethers could obviously have important consequences regarding useful, preparative routes to chiral cyclic ethers of high enantiomeric purity. For example, dioxyphos-phorane promoted cyclodehydration of a chiral diol can, in principle, give the enantiomeric ethers by either of two stereochemi-cally distinct routes. Separate stepwise decomposition of oxy-phosphonium betaines, A and B, although proceeded by a number of equilibria could ultimately afford a nonracemic mixture of cyclic ethers. 

Amberlyst-15 was also used as a catalyst for the reaction of alcohols and phenols with tetrahydropyran (Eqn. 22.33). Refluxing a mixture of an alcohol and dimethoxymethane in the presence of a Nafion-H catalyst gave the methoxy methyl ethers in very good yields (Eqn. 22.34). ° Nafion-H was also used to catalyze the conversion of diols to cyclic ethers. ... 

Diols from cyclic enol ethers. The reagent is formed in situ from TiCl and... 

Miscellaneous Reactions. - p-Toluenesulfonaraide undergoes Mitsunobu-type reactions in the presence of alcohols and cyanomethylenetriphenyl-phos-phorane (56) to give predominantly mono-N-alkylation products. This reaction has also been applied to the synthesis of cyclic ethers from diols and cyclic amines from amino alcohols and to carbon-carbon bond formation. Examples of cyclic amine synthesis include that of (+)-a-skytanthine (57). A comparative study of the reactions of active methine compounds (58) as nucleophiles using... 

Lithium tetrahydridoaluminate boron fluoride Diols and cyclic ethers from lactones... 

Acylglycosaminides—Ghange in configuration s. 14, 174 Sulfuric acid Diols from cyclic ethers s. 12, 186... 

Thus, the protective strategy in conjunction with living anionic polymerization successfully works to afford well-defined functional polystyrenes substituted with alcoholic and phenolic hydroxyl groups, diols, and triols. The silyl ether-, cyclic acetal-, and ortho ester-protected functionalities are effective for this purpose. This strategy may possibly be applied to other useful functional styrene derivatives and will be discussed in the next section. 

Diols react mtramolecularly to form cyclic ethers when a five membered or six membered ring can result... 

Conversion to dialkyl ethers (Sec tion 15 7) On being heated in the presence of an acid catalyst two molecules of a primary alcohol combine to form an ether and wa ter Diols can undergo an intramo lecular condensation if a five membered or six membered cyclic ether results... 

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