Oxirane reactions ring opening

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). 

Oxiranes undergo ring-opening with cerium(VI) ammonium nitrate and an excess of a quaternary ammonium halide to yield haloethanols [34], The reaction occurs with high regio- and stereo-selectivity, for example, / (+)-styrene oxide produces S(+)-2-chloro-2-phenylethanol in 85% yield with 96% ee. 

The 1,9-zwitterion 9, formed by the reaction of dispiro[2.0.2.4]deca-7,9-diene (8) with TCNE, is so reactive that it incorporates cyclic ethers, such as tetrahydrofuran, oxetane and oxirane, with ring opening into the macrocyclic product. ... 

Oxetanes react like oxiranes with ring-opening at a slower rate and under forcing conditions. Two reactions are of general importance ... 

The highly nucleophilic ylide anion of sodium [cyano(triphenylphosphor-anylidene)methanide] 3, which is available by deprotonation of cyano-methylene triphenylphosphorane with sodium silazanide in benzene solution at room temperature [74], attacks oxiranes by ring-opening. Depending on the work-up conditions and the further reactions employed, y-hydroxynitriles, y-butyrolactones or a-methyleno-y-butyrolactones were obtained from the primary products thus formed (Scheme 27) [16]. For in-... 

The oxirane ring-opening reaction requires the presence of a basic catalyst. An acidic catalyst also works, but the polymerization of the oxirane limits its usehilness. In the case of 2-mercaptoethanol (eq. 8), the product has been found to be autocatalytic, ie, the product is a catalyst for the reaction. 

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 parallel ability of oxiranes to undergo ring opening to carbonyl ylides was first noted in the case of tetracyanooxirane (68T2551), but such reactions have not been widely exploited. The addition to alkenes, leading to formation of tetrahydrofurans, is stereospecific (Scheme... 

The reaction of oxiranes with base can follow several paths, giving products of type (34-38 Scheme 27). (a) Formation of an oxiranyl anion (34) is rare (Section 5.05.3.5). (b) Nucleophilic ring opening to give (35) is common with unhindered bases (Section 5.05.3.4). (c) a-Elimination to give a carbene or carbenoid (36) is favored by alkyllithium bases and... 

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)... 

Epoxides are regio- and stereoselectively transformed into fluorohydrins by silicon tetrafluoride m the presence of a Lewis base, such as diisopropyleth-ylamme and, m certain instances, water or tetrabutylammonium fluoride The reactions proceed under very mild conditions (0 to 20 C in 1,2-diohloroethane or diethyl ether) and are highly chemoselective alkenes, ethers, long-chain internal oxiranes, and carbon-silicon bonds remain intact The stereochemical outcome of the epoxide ring opening with silicon tetrafluoride depends on an additive used, without addition of water or a quaternary ammonium fluoride, as fluorohydrins are formed, whereas m the presence of these additives, only anti opening leading to trans isomers is observed [17, 18] (Table 2)... 

Polymerization of oxiranes with succinic anhydride proceeded in the presence of PPL at 60 °C or 80 °C [63]. The ring-opening of the oxirane might proceed by a carboxylic acid catalyst, which is formed by the reaction of succinic anhydride with serine residue of the lipase catalyst. 

An epoxide or oxirane group can react with nucleophiles in a ring-opening process. The reaction can take place with primary amines, sulfhydryls, or hydroxyl groups to create secondary... 

Porath, 1974). B/s-oxirane compounds also can be used to introduce epoxide groups into soluble dextran polymers in much the same manner (Boldicke et al., 1988 Bocher et al., 1992). The epoxide group reacts with nucleophiles in a ring-opening process to form a stable covalent linkage. The reaction can take place with primary amines, sulfhydryls, or hydroxyl groups to create secondary amine, thioether, or ether bonds, respectively (Chapter 2, Section 1.7). 

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