Tetrahydrofuran , cyclic derivatives

Polyether Polyols. Polyether polyols are addition products derived from cyclic ethers (Table 4). The alkylene oxide polymerisation is usually initiated by alkah hydroxides, especially potassium hydroxide. In the base-catalysed polymerisation of propylene oxide, some rearrangement occurs to give aHyl alcohol. Further reaction of aHyl alcohol with propylene oxide produces a monofunctional alcohol. Therefore, polyether polyols derived from propylene oxide are not truly diftmctional. By using sine hexacyano cobaltate as catalyst, a more diftmctional polyol is obtained (20). Olin has introduced the diftmctional polyether polyols under the trade name POLY-L. Trichlorobutylene oxide-derived polyether polyols are useful as reactive fire retardants. Poly(tetramethylene glycol) (PTMG) is produced in the acid-catalysed homopolymerisation of tetrahydrofuran. Copolymers derived from tetrahydrofuran and ethylene oxide are also produced. 

Cyclic diesters are often even better substrates forlipases and esterases than acyclic derivatives. Small-ring monoacetates (28, n — 1-3) are obtained in higher yield and ee than the larger derivatives (for 28, n = 4 is only 50%) (43). Hydrolysis of tetrahydrofuran diester results in monoester (29) of ee > 99% (44). 

The influence of the size and configuration of various cyclic vinyl carriers (Scheme 6.26) on the stereoselectivity of cycloaddition was studied, and included epoxides, (3-lactams, dioxaborolanes, and dioxans (22). Although the anti preference was maintained in all cases, the conformation of the carrier ring must also be taken into account in order to rationalize the stereoselections observed. The highest diastereomeric ratio was observed with the vinyl-tetrahydrofuran derived from glucose, where the conformational mobility of the carrier ring is substantially locked by an acetonide clamp and one face of the C=C bond is effectively shielded (22,165,215). 

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 reaction of deprotonated 2-aminophenol 115 with an alkynyl-substituted Fischer carbene 277 gave a cyclic complex 279 in 40% yield, most probably via an intermediate adduct 278 (X = 0). On the other hand, complex 280, obtained from 115 and 277 without base, was heated in tetrahydrofuran to afford benzoxazepine derivative 281 (38%) and benzoxacinone 282 (36%) with reverse regiochemistry (Scheme 49) <2003CEJ4943>. 

The difference in reactivity between alkylated and acylated pentenyl glycosides can be rationalised as follows the elctrophilic iodonium ion will add to the double bond of the pentenyl moiety to give a cyclic iodonium ion. Nucleophilic attack by the oxygen will lead to an oxonium ion intermediate which then forms an oxocarbenium ion and an iodo-tetrahydrofuran derivative. The aglycone oxygen will be of low... 

A number of cyclic and sugar-derived halo acetals 273 were subjected to radical 5-exo cyclizations catalyzed by a cobalt salen catalyst 274 with NaB H4 as the stoichiometric reductant but in the presence of air (entry 11) [321, 322]. Under these conditions, bicyclic oxygenated tetrahydrofurans 275a were obtained in 50-84% yield. Diastereomeric isomers 275b were isolated as the minor components. The yields were similar to those obtained with tributyltin hydride. The oxygen concentration proved to be important, since air gave better yields... 

An efficient and operationally simple synthesis of tetrahydrofuran-derived spiro-P-lactams 15 and 16 using the Staudinger reaction of unsymmetrical cyclic ketones has been described <02JCS(P1)571 02SL69>. Similarly, spiro-P-lactams 17 were synthesized via Staudinger reaction of imines derived from 7-oxanorbomenone with alkoxyacetyl chlorides <02TL6405>. 

Spescha et al. [4] used the copper complex 6, which was obtained from a thioglucofuranose derivative, as catalyst for 1,4-additions of Grignard reagents to 3, and observed enantioselectivities of up to 60 % ee. The dihydrooxazolylthiophenolato copper complex 7 was employed by Pfaltz et al. 5] for the enantioselective catalysis of Michael additions to cyclic enones the best results were obtained with tetrahydrofuran as solvent and HMPA as additive. There was a pronounced dependence of the stereoselectivity on the ring size of the substrate 16-37 % ee for 2-cyclopente-none, 60-72 % ee for 3, and 83-87 % ee for 2-cycloheptenone. Alexakis et al. [6] used the heterocycle 8, which is readily accessible from... 

In a similar manner, Grignard reagents react with cyclic a,/3-dihalo ethers derived from 3,4-dihydro-l,2-pyran and tetrahydrofuran to form the corresponding 2-alkyl-3-halo derivatives. Thus, addition of 2,3 dibromotetrahydropyran to methylmagnesium halide at 0° followed by hydrolysis gives a 65% yield of 2-methyl-3-bromotetrahydropyran. These materials are valuable intermediates in the synthesis of olefinic alcohols (cf. method 99). 

Model experiments [43] using aliphatic alcohols (6) indicate that the main products with lead tetraacetate are cycHc ethers (mainly tetrahydrofuran derivatives) and carbonyl compounds, the product ratio depending on the solvent. Cyclic ethers are predominant in neutral non-polar solvents e.g. refluxing benzene), but carbonyl compounds are favoured by polar or basic solvents, especially p5uidine. These results were interpreted in terms of competing homolytic and heterolytic processes. The initial step is thought to be reversible formation of an alkoxy-lead triacetate (7), which may suffer either a rapid polar elimination of and Pb(OAc)s" by the action of base to give a ketone (8), or a slower homolysis of the alkoxy-lead... 

Ethanol is the key reactant in Eq. (1), and also in Eq. (2) because it is readily converted to acetaldehyde. The process based on Eq. 1 was developed in Russia and the process based on Eq. 2 was developed in the United States. The yield of butadiene for the Russian process is about 30-35%. It is about 70% if mixtures of ethanol and acetaldehyde are employed as in the U.S. process. Equation (3) represents a process that involves 2,3-butylene glycol, a product from the microbial conversion of biomass. The process is carried out in two sequential steps via the glycol diacetate in overall yields to butadiene of about 80%. The process of Eq. (4) starts with a biomass derivative, the cyclic ether tetrahydrofuran, and can be carried out at high yields. When this process was first operated on a large scale in Germany, acetylene and formaldehyde were the raw materials for the synthesis of intermediate tetrahydrofuran. It is manufactured today from biomass feedstocks by thermochemical conversion, as will be discussed later. 

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