Oxygen-containing Rings

Rings containing Oxygen. - The catalytic epoxidations of alkenes with hydroperoxides have been surveyed,as have transition-metal-catalysed stereo-controlled epoxidations. A major review of oxiran chemistry (956 references) has been published as a chapter in Saul Patai s series on the Chemistry of Functional Groups (1980).  

Theoretical aspects of the thermal and general chemical reactions of oxi-rans have been treated by the application of quantum-mechanical methods to the study of the reactions of the triplet states of isomers.  

---

Several blocked diamines or amino-alcohols are commercially available. The aldimine is an aldehyde-blocked diamine. The ketimine is a ketone-blocked diamine. The oxazolidine is a five-membered ring containing oxygen and nitrogen. The oxazolidine ring shown below is an aldehyde-blocked amino alcohol. The basic synthetic concepts of an aldimine, a ketimine, and an oxazolidine are shown below ... 

The most important sugar is glucose. It has a saturated six-membered ring containing oxygen and it is best drawn in a chair conformation with nearly all the substituents equatorial. It can also be drawn reasonably as a flat configurational diagram. 

Bromoetherification, the addition of the elements of Br and OR to a double bond, is a common method for constructing rings containing oxygen atoms. This reaction has been used in the synthesis of the polyether antibiotic monensin (Problem 21.40). Draw a stepwise mechanism for the following intramolecular bromoetherification reaction. 

Saturated heterocyclic rings containing oxygen, nitrogen, or sulfur atoms also exist preferentially in stable, chair conformations resembling that of cyclohexane. Physical measurements, such as those of electron diffraction and dipole moments, have shown this conformation for p-dioxane, -s-trioxane, ° paraldehyde, s-trithiane, and 2,4,6-trimethyl-s-tri-... 

In this third part of the series the important group of three-membered rings containing oxygen, as well as four-membered rings containing two oxygens or one sulfur, are reviewed. 

The size of coupling constants in five-membered rings containing oxygen is illustrated clearly in furfuraldehyde (furan-2-aldehyde) note how small the couplings are. 

PART II Six-Membered Rings containing Oxygen or Sulphur by G. P. Ellis... 

Special features are that the ester linkage of lactones and lactides are cleaved more easily than those of normal esters and that rings containing oxygen as ring member are the more easily cleaved the greater the number of such oxygen atoms for instance, paraldehyde is more easily cleaved than dioxan. 

Dialkyl Ethers. The asymmetric C—O—C stretching vibration leads to a single strong absorption that appears at about 1120 cm , as seen in the spectrum of dibutyl ether (Fig. 2.33). The symmetric stretching band at about 850 cm is usually very weak. The asymmetric C—O—C absorption also occurs at about 1120 cm for a six-membered ring containing oxygen. 

---