Ring-opening substituted oxirane

Olah et al.724 have shown that Nafion-H induces the ring opening of oxiranes under mild conditions to afford various products. Substituted oxiranes undergo hydrolysis or alcoholysis to yield 1,2-diols or 1,2-diol monoethers, when treated with Nafion-H under mild conditions in the presence of water or alcohols, respectively. Cycloalkene oxides give the corresponding trans products stereoselectively [Eq. (5.273)]. 

Carbene eomplex anions are suitable C-nueleophiles for the ring-opening of oxiranes. The resulting alkoxide intermediates undergo a subsequent cyclization to give 2-oxaeyelopentylidene complexes 9 (Seheme 6). Unsymmetrically substituted epoxides are attacked by the earbene anion at the less hindered carbon atom. 

Ring opening of oxiranes is catalyzed by zirconium or hafnium complexes in the presence of nucleophiles. Cp2ZrCl2 was used as a catalyst for ring opening of substituted epoxides with alcohols under mild conditions. The corresponding alkoxyalcohols were obtained in good yields. As shown in Equation 38, when trans-stilbene oxide was subjected to the reaction in methanol, a mixture of anti-and syn isomers were obtained [43]. 

Ring-opening nucleophilic substitution Ring opening of oxiranes... 

Scheme 4-205. SN -type ring opening substitution of alkynyl oxiranes by Grignard reagents catalyzed by tris(acetylacetonato)iron.

Some examples of ring opening reactions with carbanions leading to five-membered heterocyclic ring formation are shown in Scheme 85. Pyrrole syntheses from functionally substituted oxiranes and amines are often described and typical examples are shown in Scheme 86. 

The oxaziridine ring itself is stable towards alkali there is, for instance, no substitutive ring opening by hydroxyl ions as in oxiranes. 2-r-Butyl-3-phenyloxaziridine (56) is not attacked by methoxide ion in methanol during 12 h at room temperature 3-isopropyl-2-r-octyloxaziridine does not react at room temperature with either solid potassium hydroxide or potassium methoxide solution (57JA5739). 

The combination of alkali metal acid fluorides and porous aluminum fluoride IS a stable, solid, and efficient substitute for anhydrous hydrogen fluoride for promoting the ring-opening reactions of simple aliphatic oxiranes to give the fluorohydrins under sonication [/5] (equations 14 and 15)... 

In a scheme intended to produce a more highly substituted oxazolidone, epichlorohydrin is condensed with morpholine in the presence of strong base to give the aminoepoxide, 27. Ring opening of the oxirane by means of hydrazine gives the hydroxy-hydrazine (28). Ring closure with diethyl carbonate leads to the substituted oxazolidone (29). Condensation with 18 affords furaltadone (30). ... 

Oxiranes undergo ring opening with trialkylsilyl chlorides to yield trialkylsilyl chloroethyl ethers [51]. The reaction has been shown to be catalysed by tetra-n-butylammonium chloride, although most studies have used triphenylphosphine as the catalyst. Substituted oxiranes are cleaved by haloalkanes to yield the corresponding l-ch oro-2-aIkoxy-2-substituted alkanes [52] (see Section 9.3). 

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