Oxolane, structure

High-valency metal fluoride fluorination of pyridine [82JFC(21)171], quinoline [82JFC(21)413], and 2-methylfurans [91 JFC(51)179] has been reported. With 2-methylfuran a complex mixture of stereoisomers of partially fluorinated oxolans was obtained. These can be dehydrofluorinated to fluorooxolens and no furans have been observed. Conformation and structural group were found to influence the direction and readiness toward dehydrofluorination [91 JFC(52) 165]. 

The silylation reactions were performed by treatment of a solution of the substrate (1 mol. equiv.) in oxolane [or a A 1 (v/v) mixture of oxolane—dimethyl sulfoxide for substrates insoluble in oxolane] with (l.A—1.5 mol. equiv.) and trlphenylphosphine (0.5 mol. equiv.). The structures of the substrates employed and of the products obtained, and yields, are shown in Figure 1. Under the particular reaction conditions employed secondary hydroxyl groups are either not silylated or are silylated distinctly slower. 

The reactivity of the 2,5-anhydrides of aldoses is determined by two essential structural features that do not exist in the sugars, namely, the presence of an oxolane ring and of a carbonyl group (most frequently, free) a to the ring-oxygen atom. These two characteristics make the 2,5-anhydroaldoses closer to tetrahydro-2-furaldehyde than to the aldoses, where only in exceptional cases is the carbonyl group not masked by the formation of an intramolecular, five- or six-membered, hemiacetal ring. 

In 1987, studying the possibility of using different electrophiles in Sinay s C-glucosydation procedure (Scheme 1) based on the Wittig-mercuriocyclization approach, (8) we observed that the use of iodine in oxolane-water at pH 4 resulted in the formation of the furanosidic structure 6. (9)... 

The use of an unsaturated nucleophile to introduce into the chain end of the macromolecule a double bond has also proved successful for the synthesis of poly-THF macromonomers. The oxolane polymerization is started with any efficient initiator. When the growing chains have reached the desired length, the unsaturated deactivator is added. The reaction between the oxonium sites and the nucleophile should be fast and free of side reactions. Various unsaturated nucleophiles have been employed, e.g. p-vinylphenoxide used by Asami50). The THF polymerization was initiated with triethyloxonium tetrafluoroborate and carried out atO °C. Addition of the nucleophile (obtained by reaction of the phenol with NaH) yields the corresponding macromonomer the structure of which was characterized by various techniques ... 

Besides the initiation with the vinyl ether adducts, trimethylsilyl halides in conjunction with oxolane [135] or a carbonyl compound [136-141] also provide an interesting method of end-functionalization. As discussed in Chapter 4, Section V.E.2 (also Figure 9 therein), the a-end group is (CH3)3SiO—, derived from the silyl compound, to be converted into the hydroxyl group [140,141], Depending on the structure of the carbonyl compounds, it is either secondary (from aldehyde) [136-139] or tertiary (from ketone) [137,138,140,141], both of which are difficult to obtain from the vinyl ether adducts (note that the adduct of AcOVE leads to a primary alcohol [30,31]). 

The properties of four-coordinate Si centers bonded to an alkylenedioxy substituent derived from a furanoidic diol also were investigated with the two isomeric oxolane-3,4-diols AnEryt and L-anhydrothreitol [92]. Thus, substitution of silicium with two phenyl residues leads to Ph2Si( AnErytH 2) 85 in the case of AnEiyt. The molecular structure is that of a monomer. The five-membered chelate ring is almost planar, with a diol torsion angle close to 0°. Such geometrical parameters cannot be met by L-AnThre. However, this diol provides another example... 

As an even more valuable asset for mechanistic investigations, any structural changes during product formation can be unravelled by analysing where in the product the labels show up. Figure 20 provides a nontrivial example. In the photoreaction of benzoquinone with quadricyclane, the polarizations arise from fhe 1,5-biradical BRi. The singlet exit channel leads to the oxolane Pi, the triplet channel to the oxetane P2. The structure of the quadricyclane-derived moiety in BRi is identical to that in Pi but quite different from that in P2, so obviously Pi is formed by a simple combination of the radical centres whereas an extensive skeleton... 

Isomaltulose, also known as Palatinose (lUPAC name (2R,3R,4S,5R,6S)-2-(hydroxymethyl)-6-[[(2R,3R,4S)-3,4,5-trihydroxy-5-(hydroxymethyl)oxolan-2-yl]methoxy] oxane-3,4,5-triol), and sucrose have similar physical and organoleptic properties. Isomaltulose (Palatinose ) is a reducing, free-flowing, non-hygroscopic crystalline compound which can be crystallized easily from aqueous solutions with one mole crystal water. Crystalline isomaltulose (Palatinose ) melts at 123-124 The crystal structure and... 

Scheme 11.13. A representation of a portion of the pathway of gluconeogenesis. The 6-phosphate of glucose is considered capable of hydrolysis to glucose with the appropriate hydroiyase (EC 3.1.3.9) catalyst. The anomer shown is a (because the hydroxyl on the ano-meric carbon is cis or syn to the hydroxyl at C5, Scheme 11.14). A caution concerning nomen-ciature is needed. In the acyclic form, it is clear which carbon is number six. Cyclization to the six-membered ring pyranose (oxane) (or furanose [oxolane] when the five-membered ring forms) leaves ns with a nomenclature problem since the carbon that was C-1 (the ano-meric carbon) is often referred to as C-1 in both structures that involve formation of bonds to that carbon as well as in reactions that may occur at that carbon. However, it will be recalled (Chapter 5) that the nomenclature of cyclic ethers (and other heterocycles) generally requires that the heteroatom (or a heteroatom if more than one is present) receive the lowest number. So, the lUPAC and the lUBMB numbering system is used for archiving purposes, while the trivial nomenclature is commonly used in the literature. Both systems will be found here as appropriate.

Monosaccharides occur as substances with a free carbonyl group (acyclic compounds) and as cyclic hemiacetals, also called lac-tols. Trioses are exclusively acyclic substances, tetroses and higher monosaccharides exist predominantly in five- and six-membered and, exceptionally, also in seven-membered cyclic structures. They can therefore be regarded as substances derived from oxolane (tetrahydrofuran), oxane (tetrahydropyran) or oxepane, and are thus actually heterocyclic compounds. Acyclic forms, which exist in constitutional equilibrium with cyclic forms, occur in zigzag conformers, as well as alditols (see Section 4.3.1.1.1). 

The same reaction has been performed with partially chloromethylated polystyrene as backbone. On addition of silver hexafluoroantimonate in THF solution, the benzylic cations formed can initiate the polymerization of THF to grow the grafts. However, living poly(oxolane) reacts readily with benzylic halides, whereby the chain is terminated and another site is created (Scheme 24). In other words, transfer also contributes to the grafting process. The grafted structure... 

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