Heterocycles containing Two Oxygen Atoms

S Heterocycles containing Two Oxygen Atoms Dioxans. - The cis- and the frans-isomer of 2-methyl-3-phenylbenzodioxan have been synthesized by aluminium-chloride-catalysed cyclization of threo-and e/jf/jra-l-phenyl-2-(2-hydroxyphenoxy)propanols, for example the threoA omex (247). A highly substituted dioxan (248) has been synthesized by treatment of 2-ethoxypent-l-en-3-ol with a catalytic amount of toluene-p-sulphonic acid at 20 °C, but the dihydrodioxin (249) was formed, in 70% yield, when the reactants were heated.  

3-dioxans (254 R = alkyl) and (255 R = H or Pr ) have been shown by and n.m.r. spectroscopy to have chair forms and equatorial substituents. Dioxan is cleaved by treatment with trimethylsilyl 

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REDUCTION OF HETEROCYCLES CONTAINING TWO OXYGEN ATOMS OR TWO SULFUR ATOMS... 

REDUCTION OF HETEROCYCLES CONTAINING TWO NITROGEN ATOMS AND ONE OXYGEN ATOM... 

Heterocycles containing an Oxygen Atom in each of Two or More Rings... 

The syntheses of five-membered heterocycles containing three oxygen or sulfur atoms in the 1,2,3-positions can be classified into three groups (i) one-component syntheses, in which a suitable acyclic molecule is cyclized by linkage of two heteroatoms (ii) two-component syntheses, in which the ring is built up either by a [3 -f 2] process or a [4 -1-1] process and (iii) synthesis by transformation of another heterocyclic ring. 

HETEROCYCLES CONTAINING TWO OR MORE OXYGEN ATOMS 643.1 Dioxins... 

Isoxazole, pyrazole and isothiazole constitute the 1,2-azole family of heterocycles that contain two hetero-atoms, one of which is a nitrogen atom. The second hetero-atom is oxygen, nitrogen or sulphur, respectively. 

The ability of sulfur to stabilize an adjacent anion will be discussed in Chapter 46, and it means that sulfur heterocycles are much easier to deprotonate than THF. The most important of these contains two sulfur atoms dithiane. Deprotonation of dithiane occurs in between the two heteroatoms, and you can see some chemistry that arises from this on p. 1234. For tire moment, we will just show you series of reactions that illustrate nicely both dithiane chemistry and the ring opening of oxygen heterocycles in the presence of BF3, This substituted derivative of dithiane is deprotonated by BuLi in the same way to give a nucleophilic organolithium that will... 

MR-Ri exhibited the molar refractivity effect of only Ri-substituent. In Eq. 40, Id-02 is an indicator variable that was assigned a value of 1 for a molecule containing a heterocycling ring with two oxygen atoms. Obviously such a heterocyclic ring did not seem to be of advantageous. 

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