Epoxide ring, opening synthesis

The asymmetric epoxidation of electron-poor cinnamate ester derivatives was highlighted by Jacobsen in the synthesis of the Taxol side-chain. Asymmetric epoxidation of ethyl cinnamate provided the desired epoxide in 96% ee and in 56% yield. Epoxide ring opening with ammonia followed by saponification and protection provided the Taxol side-chain 46 (Scheme 1.4.12). 

In the synthesis of the bromo derivative 12 from diepoxide 11, an interesting epoxide ring-opening-ring-closure reaction is involved.5... 

The potential of such reaction sequences for the generation of molecular diversity was also demonstrated by the synthesis of a library of heterocycles. Epoxide ring-opening with hydrazine and subsequent condensation with (3-diketones or other bifunctional electrophiles gave rise to a variety of functionalized heterocyclic structures in high purity [34]. A selection based on the substrate derived from cyclohexene oxide is shown in Scheme 12.12. 

Some additional examples are given in Scheme 8.6. The electrophiles that have been used successfully include iodine (Entries 2 and 3) and cyanogen chloride (Entry 4). The adducts can undergo conjugate addition (Entry 5), alkylation (Entry 6), or epoxide ring opening (Entries 7 and 8). The latter reaction is an early step of a synthesis of epothilone B. 

An alternative disconnection of homopropargylic alcohols substrates for intramolecular hydrosilylation is the opening of an epoxide with an alkynyl anion. This strategy was employed in a total synthesis of the macrolide RK-397 (Scheme 20). Epoxide ring opening serves to establish homopropargylic alcohol C with the appropriate stereochemistry. A hydrosilylation/oxidation protocol affords the diol E after liberation of the terminal alkyne. The... 

Epoxide ring-opening with transfer of an sp carbon moiety was applied in a short synthesis [44] of eicosanoid 56 [45], relevant in marine prostanoid biosynthesis (Scheme 9.13). Homoallyl alcohol 55 was obtained in good yield from 54 by use of a cyano-Gilman alkenylcuprate [46]. 

The synthesis of fluoroazoles usually involves a chiral epoxide ring opening by the azole, as exemplified by the synthesis of albaconazole (Figure 8.24). 

Polyaniline-supported Co(II) catalyst 41 was used to catalyze the epoxidation of various alkenes under oxygen atmosphere at ambient temperature.61 63 One report61 described a synthesis of a-hydroxy- 3-aminopyrrolidine amides as potential HIV protease inhibitors (Scheme 1). In this synthesis, catalyst 41 also mediated epoxide ring opening of the epoxide intermediate by an aniline to afford the desired product. 

The synthesis of tetrahydrofurans through cyclization via epoxide ring opening has been well investigated and has been applied to the preparation of a-bisabolol oxides (69IJC1060) and linalool oxides (77H(6)1365) and by Kishi et al. in the synthesis of lasalocid A (195), where the epoxide pathway resulted in a stereospecific construction of six out of the ten chiral centers (Scheme 93) (78JA2933). 

Narjes, F. Bolte, O. Icheln, D. Konig, W. A. Schaumann, E. Synthesis of vinylcydopro-panes by intramolecular epoxide ring opening. Application for an enantioselective synthesis of dictyopterene A. /. Org. Chem. 1993, 58, 626-632. 

Konno, H. Toshiro, E. Hinoda, N. An epoxide ring-opening reaction via a hyperva-lent silicate intermediate synthesis of statine. Synthesis 2003, 2161-2164. 

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