Transformations of Epoxides

Epoxidation may be preliminary to solvolytic or nucleophilic ring opening in synthetic sequences. In acidic aqueous solution, epoxides are opened to give diols by an 

SECTION 12.2. ADDITION OF OXYGEN AT CARBON-CARBON DOUBLE BONDS 

Base-catalyzed reactions, in which the nucleophile provides the driving force for ring opening, usually involve breaking the epoxide bond at the less substituted carbon, since this is the position most accessible to nucleophilic attack.86 87 The situation in acid-catalyzed reactions is more complex. The bonding of a proton to the oxygen weakens the C—O 

Epoxidation followed by ring opening to an allyl alcohol 

When simple aliphatic epoxides such as methyloxirane react with hydrogen halides, the dominant mode of reaction introduces halide at the less substituted primary carbon.88 

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Functional group transformations of epoxides rank among the fundamental reactions of organic chemistry and epoxides are commonplace natural products The female gypsy moth for example attracts the male by emittmg an epoxide known as disparlure On detechng the presence of this pheromone the male follows the scent to its ongm and mates with the female... 

An enantioconvergent transformation leads to a single enantiomeric product from a racemate [51]. Each enantiomer is transformed via independent pathways by the same catalyst or by two different catalysts (Figure 6.6). For example, the hydrolysis of epoxides may proceed with high regio- and stereoselectivity vdth inversion or retention of configuration. Several enantioconvergent transformations of epoxides are reported in the last section of this chapter. 

H. Kotsuki, T. Shimanouchi, R. Ohshima, and S. Fujiwara, Solvent-free organic reactions on silica gel supports. Facile transformation of epoxides to /i-halohy-drins with lithium halides, Tetrahedron, 54 (1998) 2709-2722. 

Karpf, M. et al. New, Azide-Free Transformation of Epoxides into 1,2-Diamino Compounds Synthesis of the Anti-Influenza Neuraminidase Inhibitor Oseltamivir Phosphate (Tamiflu). 3.4.4 2001 [135]... 

Catalytic Ring-Opening and Ring Transformations of Epoxides 10.2.3.1 Achiral Catalysts... 

A mild and highly stereoselective transformation of epoxides to azido alcohols by treatment with Et3Al-HN3 in toluene has been reported (Scheme 65). ... 

These mixed bridged-dinuclear Rh complexes [Rh2(//-Cl)(//-SR)(CO)2(PR 3)2] also catalyze the transformation of epoxides or unsaturated alcohols into the corresponding ketones [39]. 

Episulfides. The transformation of epoxides into episulfides by means of ammonium thiocyanate in refluxing MeCN is promoted by BiCl, (7 examples, 96-99%). 

Transformation of epoxides (238) into thiiranes (239) are first carried out in the presence of potassium thiocyanate in the absence of both solvent and phase-transfer catalysts (Equation (37) and Tables 38 and 39). 

The thermal instability of the telluriranes is also utilized in the transformation of epoxides to alkenes <77CC658, 80JOC2347). When epoxides are treated with sodium 0,0-diethyl phos-... 

The transformation of epoxides to allylic alcohols by the use of lithium dialkylamides is well known Consequently, it should be possible to apply this reaction to the asymmetric synthesis of allylic alcohols by the selective deprotonation of the enantiotopically related protons in symmetrical epoxides. 

Functional group transformations of epoxides rank among the fundamental reactions of organic chemistry, and epoxides are commonplace natural products. The female... 

P-Chloroalkyl esters. These reagents enable transformation of epoxides to /3-chloroalkyl esters without simultaneous generation of HCl therefore, potentially sensitive compounds (acrylate, etc.) are prepared cleanly. The silica-linked hexa-butylguanidinium chloride is particularly effective. 

An extraordinarily simple approach to a Fischer indoli-zation is that of Taylor and Donald [120] involving the transformation of epoxides to indoles via aldehydes or ketones (the Meinwald rearrangement) in the presence of arylhydrazines, and thence to indoles, obviating the need for isolating the carbonyl compound. Selected examples of this simple chemistry are shown in Scheme 18 (equations 1, 2). Of the Lewis acids screened, scandium(III) triflate proved to be superior. Greaney and colleagnes... 

The Julia-Kocienski olefination has inspired McGeary and coworkers to develop the transformation of epoxides 54 into the corresponding alkenes fScheme 19.28T In a first step, the nucleophilic addition of the BT-thiol 55 to the epoxide 54 afforded the p-hydroxy BT-thioether 56, which can fiirther evolve under prolonged reaction time to give the episulfide 57... 

Similar transformations of epoxides bearing an alkyne unit were reported to occur in the presence of HAUCI4 [181], Ph3PAuBp4 [182], and Cu(II) triflate-iodine [183] catalytic systems. The first two protocols offer an attractive route to the synthesis of differently substituted difurylmethanes, whereas the latter provides an easy and modular access to up-to-tetrasubstituted 3-iodofurans. 

Uneyama K, Isimura A, Fuji K, Torii S (1983) Electrogenerated acid as a powerful catalyst for transformation of epoxides to ketones and acetonides. Tetrahedron Lett 24 2857-2860. doi 10.1016/S0040-4039(00)88043-0... 

Transformations of epoxides may also be useful In Inactivating trichothecene epoxides, as evidenced by the following relevant observations ... 

Abstract Transformation of epoxides is a key step for numerous processes important both for synthetic organic chemistiy and biochemistry. Since experimental methods are restricted by the fixation of sonrce compoimds, intermediates and prod-nets of reactions, quantum chemical calculations serve as the only direct approach for prediction of the structure and energy of transition states thus clarifying detailed mechanisms of chemical reactions. This chapter stunmarizes resrrlts of quantum chemical investigation of epoxides transformation mechanisms in alkaline, neutral and acidic environments. Special attention has been paid to stereo- and regiochem-istry of the processes, influence of solvation effects and natrrre of catalytic action of mono- and bidentate acids. 

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