Saturated Oxygen Heterocycles

The most widely used method for the preparation of epoxides involves oxidation of an aUcene by a peracid, °° via a direct one-step transfer of an oxygen atom. More highly (alkyl) substituted alkenes react fastest showing that electronic effects are more important than steric effects in this reaction. Steric effects do, however, control the facial selectivity of epoxidation conversely hydrogen-bonding groups, such as OH and NH, can direct the reaction to the syn face. 

Epoxides and oxetanes can also be prepared by cyclisation of 1,2-halohydrins and 1,3-halo-alcohols.  

Oxetanes have often been prepared by the Paternd-Buchi reaction, ° in which a compound containing a carbon-carbon double bond cycloadds to an aldehyde or ketone under the influence of light.  

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Reviews of saturated oxygen heterocycles <00JCS(P1)1291>, routes to 2,2-dimethyl-2H-[l]benzopyrans <00H(53)1193> and pyranonaphthoquinone antibiotics <00T1937>, HIV-1 active Calophyllum coumarins <00H(53)453> and of the application of (3-halovinylaldehydes in heterocyclic synthesis <00H(53)941> have appeared. 

Reviews of thietanes <99MI138> and saturated oxygen heterocycles including oxetanes are available <98JCS(P1)4175>. 

Some of the most important saturated oxygen heterocycles are the sugars. Glucose is a cyclic hemiacetal—a pentasubstituted tetrahydropyran if you like—whose major conformation in solution is shown on the right. 

Syntheses of saturated oxygen heterocycles with lead tetraacetate ... 

Six-membered, saturated oxygen heterocycles are also very common in various types of natural products, and catalytic hydrogenation is often the method of choice for the introduction of stereocenters in a highly diastereoselective fashion. 

This class of saturated oxygen heterocycles has been made in a variety of different ways (Figure... 

Catechins (Figure 6.14) have two benzene cycles bonded by a saturated oxygenated heterocycle (phenyl-2 chromane nucleus). This structure has two asymmetrical carbons (C2 and C3) that are the origin of the four isomers. The more stable forms are (+)-catechin and (-)-epicatechin. 

Many of the stereoelectronic effects in the list above govern reactivity, but the next section will deal with how stereoelectronic effects affect structure—and in particular conformation. Some of the most important saturated oxygen heterocycles are the sugars. Glucose is a cyclic hemiacetal—a pentasubstituted tetrahydropyran if you like—whose major conformation in solution is shown below. About two-thirds of glucose in solution exists as this stereoisomer, but hemiacetal formation and cleavage is rapid, and this is in equilibrium with a further one-third that carries the hemiacetal hydroxyl group axial (<1% is in the open-chain form). 

M. Brimble, In J. Cossy, editor Synthesis of Saturated Oxygenated Heterocycles Topics in Heterocyclic Chemistry, Vol. 35 and 36, Springer Heidelber, New York, Dordrecht, London (2014). 

Ethylene oxide 3 may be cyclodimerized to 1,4-dioxan 4 in the presence of superacids, like chlorosulfonic or perchloric acid (Equation 1). The reaction was accelerated by aprotic dipolar solvents, but was retarded by less polar solvents. Chlorosulfonic acid also catalysed ring-opening polymerization of the saturated oxygen heterocycle oxepine 5 to the polymer 6 (Equation 2). ... 

J. Cossy (ed.). Synthesis of Saturated Oxygenated Heterocycles /, Topics in HeterocycUc Chemistry 35, DOI 10.1007/978-3-642-41473-2 2,... 

Finally, I hope that this book will be a good source of inspiration for those planning the synthesis of saturated oxygenated heterocycles, for solving specific synthetic problems, or for elaborating on new synthetic tools. 

Platinum-mediated additions of alcohols to alkenes are known in their intramolecular version and have been developed by R. A. Widenhoefer and coworkers [142]. Thus, they showed that [ PtCl2(H2C-CH2)]2]/2P(4-C6H4CF3)3 is an effective catalyst for the intramolecular cyclization of 7- and 8-hydroxyolefins to saturated oxygen heterocycles under mild reaction conditions [143] (Scheme 78). 

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