Regiospecificity oxirane ring-opening

The next key series of reactions results in the transformation of 625 to 626. The first step is a Sharpless epoxidation of the allylic alcohol. This is followed by a regiospecific oxirane ring opening with potassium benzyloxide to introduce the required oxygen that will eventually... 

Pyridazines have been prepared from a variety of other heterocyclic systems and in most cases these transformations were specific. The 3(S), 4(5) 36, a constituent of the antibiotic antitumor luzopeptin A, was prepared in a multistep synthesis from malonaldehyde dimethyl acetal in 32% overall yield. In the last step a highly regiospecific nucleophilic ring opening of the glycidic acid (oxirane derivative) took place (89JOC3260). In another example, c75,frani-l,3-cycloundecadiene was transformed in five steps in low yield into 59. In the last step the epoxide 58 was treated with excess of LDA (89TL4649). 

Cyclic carbonates have been prepared in the regiospecific ring-opening of oxiranes by butyrolactones catalysed by the quaternary ammonium salt (Scheme 3.6)... 

Interestingly, cyclopropane 245 (R = SPh) is also formed when 243 is combined with (trimethylsilyl)oxirane. In this case, the necessary alkene (phenylthioethylene) is provided by silanolate elimination from the alkoxide arising from regiospecific ring-opening of the oxirane by thiophenolate (equation 82)142. 

An investigation of the effect of various catalysts, the solvent, and alkyl groups on the oxirane ring28 has shown that for ring opening with cyanide ion the best yields are obtained when the catalyst is (16) and the solvent is ethylene glycol. The reactions are regiospecific at the least substituted carbon and occur rapidly at room temperature,... 

Many authors elucidated functionalization of polymers containing reactive oxirane moieties. Epoxidized NR, BR, IR and/or the respective model hydrocarbons, poly (butadiene-co-isoprene, various epoxy resins, poly (2,3-epoxypro-pyl methacrylate) and its copolymers or grafted systems were mostly exploited. Stabilizers based on epoxidized unsaturated rubbers are of the top interest. The mechanism of the functionalization process was studied in details by means of 3,4-epoxy-4-methylheptane and 1,2-epoxy-3-ethyl-2-methylpentane as model compounds [289]. The ring opening of the asymmetric oxirane is regiospecific. Aliphatic primary amines attack the least substituted carbon atom and can be involved in crosslink formation. Aromatic primary and secondary amines are less reactive than aliphatic ones because of their lower basicity the attack on the least substituted carbon atom is however preferred too. 

Reduction with LiAlH4 is an Sjv2-type reaction " the complex anion attacks as a hydride-carrier on the side opposite to the oxirane ring if there is no steric hindrance, the ring is opened regiospecifically at the least-substituted carbon atom and yields the more-substituted alcohols. The reactivity increases in the sequence UBH4, UAIH4, and Li(sec-Bu)2BH. Examinations on optically active 1-aryl-l,2-epoxypropane and 2-aryl-2,3-epoxybutane, and 1-phenyl- and... 

Heathcock and cowoikers in the course of their synthesis of vemolepin reacted the oxirane (8) with the diethylaluminum alkynide (9), when regiospecific ring opening of the oxirane occurred, leading to (10 Scheme 19). Interestingly, the stereoisomer (11) did not react under the same conditions. 

In their synthesis of erythionolide B (21), Corey and cowoikers used two alkylations of an alkynide ion in the preparation of one half of the molecule. One alkylation involved regiospecific ring opening of a resolved oxirane to provide the desired compound with the correct absolute stereochemistry, while the second used a simple methylation (Scheme 40). 

TL8999>. Triisopropyl (TIPS) acyl silanes have been prepared by a regiospecific ring opening of TIPS-substituted oxiranes with cyanocuprates and subsequent oxidation of the resulting alcohols. 

The 1 1 complex formed between ZnCla and tetramethyl-2-tetrazene reacts with cyclo-octene and oxygen to give solely the oxiran, whereas with styrene the reaction goes further, the intermediate oxiran ring being opened regiospecifically to produce the amino-alcohol PhCH(OH)CH2NMe2. ... 

A novel ring-opening reaction of oxirans, catalysed by copper and pyridine, generates c/s-diols under mild conditions. The bicyclic epoxides (186 = 1 or 2) yield (187 n = 1) (95%) and (187 = 2) (85%) in neutral, phosphate-buffered, solution. This type of reaction may have some relevance to the metabolic pathways for fused aromatic compounds, which are thought to proceed via arene oxides and diol epoxides. The catalyst system may be used to add OH", Cr, or MeO regiospecifically to the benzylic centre of indene oxide, with proton addition to the oxygen atom of oxiran. 

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