Oxirane ring compounds

The geometries of oxiranes have been determined mainly by X-ray diffraction on crystalline natural products, the oxirane ring being widespread in nature (Section 5.05.5.3). However, the detailed structure of the parent compound (Figure 1) has been secured by microwave spectroscopy and electron diffraction studies (64HC(l9-l)l). The strain in this... 

The one group of cyclic ethers that behaves differently from open-chain ethers contains the three-membered-ring compounds called epox.id.es, or oxiranes,... 

In another interesting application of this procedure, the acid-mediated cascade cyclization of (3-diketone diepoxide 73 involves the participation not only of the two oxirane rings and of the secondary alcoholic group, but also of one of the two carbonyl groups. In this way, besides the two adjacent C and D THF rings, the simultaneous construction of the spiroketal function between the B and C rings of etheromycin is obtained (compound 74, in a 70 30 mixture with 12 -epi compound Scheme 8.19) [37]. 

Reductive opening of the oxirane ring of 193 with lithium aluminum hydride, and acetylation, provided compound 194. Epoxidation of 194 with mCPB A gave the epoxide 195. Opening of the oxirane ring with acetate ions, followed by acetylation, gave the tetraacetate 196, or, by exhaustive acetylation with acetic anhydride-DMAP, the pentaacetate 189. Compounds 196 and 189 were readily transformed into 190 by hydrolysis. " ... 

The principle of active-site-directed inactivation of glycosidases by gly-con-related epoxides can be extended to compounds having an exocyclic oxirane ring, either directly attached to the six-membered ring (32) or at some distance (33,34). Studies with -o-glucosidase from sweet almonds and intestinal sucrase-isomaltase revealed that, in spite of the higher intrinsic reactivity of these epoxides, this shift of the position of the epoxide function causes a 10- to 30-fold decrease of kj(max)/Ki, an effect which probably reflects the limited flexibility of the catalytic groups involved in the epoxide reaction. 

Carbonyl compounds, such as aldehydes [103, 179], (thio)ketones [31, 94, 180-183], carboxylic acids, and esters [183, 184] with 1 are reduced to alcohols after hydrolysis [5], except in stericaUy hindered cases (see Section 8.5) [185, 186]. Under the same experimental conditions the regioselective reduction of the oxirane ring with 1 gives also the corresponding alcohol [183, 187]. 

A comparative analysis of the IR spectra of monomers under study and known model compounds (tetraalkylstannanes and unsaturated oxiranes) indicates corresponding shifts of absorption bands for the oxirane ring and the Sn—C bond. 

Since acidity (Lewis or Brpnsted) impacts adversely on the yield of epoxides, Clerici and Ingallina (204) added basic compounds in low concentrations to TS-1 catalysts during epoxidation of alkenes to inhibit the oxirane ring opening and enhanced the epoxide yields. A comprehensive investigation of the influence of pH on product selectivity in epoxidation of allylalcohol, allylchloride, and styrene catalyzed by various titanosilicates was reported recently by Shetti et al (205). 

Haloalkene oxides form a particular group of xenobiotics generally known for being reactive and toxic. Here, we discuss two classes of compounds, separated according to the vicinal or geminal position of their halogen atom(s) relative to the oxirane ring. 

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