Epoxides preparation

Quinidine, a natural product epimeric with quinine at Cg and C9, was accessed through the diastereoisomeric trans epoxide prepared from 86 by SAD, in this case by using AD-mix a [2b, 41]. 

Examples for straightforward epoxide preparation from natural sources can be found in carbohydrate chemistry [28,29]. Deoxygenations of such compounds are shown in Scheme 4. 

Scheme 4.43 Ring-opening reaction of epoxides prepared by Shi s asymmetric epoxidation.

Figure 13 shows the structure and absolute configuration of (2R,3S)-(-) vitamin K3 epoxide. This epoxide, prepared in optically active form by us (70) in 1976, had been known as a racemate since 1939 (78). It has recently been implicated (79) in prothrombin biosynthesis (80). The absolute configuration as shown in Figure 13 is based on the work of Snatzke (76) and the absolute rotation is [ ]436 = — 124° (acetone) and [a] = 0° ( ) (acetone). 

In contrast to the epoxides, preparative routes to the aziridines are fairly evenly split between the [C=N + C] and the [C=C + N] routes. Among contributions in the former category, aziridine carboxylate derivatives 110 can be prepared through the lanthanide-catalyzed reaction of imines with diazo compounds, such as ethyl diazoacetate (EDA). In this protocol, iV-benzyl aryl aldimines and imines derived from aromatic amines and hindered aliphatic aldehydes are appropriate substrates <99T12929>. An intramolecular variant of this reaction (e.g.. Ill —> 112) has also been reported <990L667>. 

Among the simplest epoxides prepared by way of a 1,2-diol monotosylete are glycidol, synthesized by Sowden and Fischer1 13... 

An inversion mechanism had been previously observed in the hydroxylation of caranine (2) to lycorine by Wildman and Heimer. They observed 7% incorporation of [2/ -3H] caranine into lycorine in Zephyranthes Candida Herb., the 3H being retained at C-2 of 1 as shown by the conversion into the inactive 385. The stereospecifically labeled precursor was obtained through LiAl3H4 reduction of lycorine-1,2-a-epoxide prepared from lycorine via its cis-chlorohydrin and chromatography on Florisil. The structure of the a-epoxide rests on physical and chemical grounds, whereas the stereochemistry of the... 

Agency for Toxic Substances and Disease Registry, Toxicological Profile for Hep-tachlor/Heptachlor Epoxide. Prepared by Clement International Corporation, under Contract No. 205-88-0608, U.S. Public Health Service, TP-92/11, 1993, (Update) PB/93/182467/AS. 

Okuma, K., Tanaka, Y., Kaji, S., and Ohta, H. (1983) Reaction of Dimethyl-oxosulfonium methylide with epoxides. Preparation of oxetanes. Journal of Organic Chemistry, 48, 5133-5134. 

P = 1) systems while the apparent activation energy markedly decreases in the same series AEapp for the linear polymer DGER-AN is close to the typical value for many polymers 57 59). The results testify that the fragment (segment) of the network which is responsible for a-transition is in average smaller than that of a linear polymer. The temperature range of the T transition for the networks is markedly narrower than that for linear polymers and epoxides prepared from industrial resins 13,19). This points to a narrower distribution of relaxation times in the considered networks as compared with other crosslinked polymers. 

Utility Epoxide Preparation Using Insitu Diazo Intermediates... 

The Chemistry of Ring A.—Two methods have been described for smoothly hydrolysing the highly-hindered axial C-4 methyl esters such as methyl 0-methyl podocarpate. The first uses boron trichloride in methylene chloride, and the otherlithium n-propyl mercaptide in hexamethylphosphoramide. The oxidative decarboxylation of dehydroabietic acid and 0-methyl podocarpic acid affords a mixture of C-4 olefins which are separable over 10 % silver nitrate by t.l.c. Thus in a partial synthesis of callitrisic acid, the 4(19)-epoxide prepared... 

An alternative approach to epoxides utilizes aldehydes or ketones instead of alkenes as precursors for epoxide preparation. 

Corey-Chaykovsky epoxidation Preparation of epoxides from aldehydes and ketones. 102... 

A double nucleophilic attack by benzylamine on a symmetric bis-epoxide, prepared from D-mannitol, was used in a recent synthesis of 250 [564], In another recent report, 5-keto-D-glucose was reacted with diphenylmethylamine and sodium cyanoborohydride in a key step in the formation of 250 [565]. 

Terpenes epoxides, prepared by the straightforward oxidation of their unsaturation [9], have also been submitted to cationic polymerization [5, 10] and to insertion copolymerization with C02 [11], but these studies were not systematic in their approach. 

The addition of aldehydes to carb - rCHN, to form stilbene epoxides prepared from 10-mercaptoisobc Jes derived from 48 on aldehydes i - -nciple underlies a synthesis of chn... 

Access to new cyclitol thiirane derivatives has been reported by reaction of cyclitol epoxides with dimethylthioformamide in trifluoroacetic acid. For example the episulfide analogue 90 was produced from the conduritol B epoxide compound 91. Several similar examples were described starting from cyclitol epoxides prepared by known methods. 

The postulated epoxide intermediates in the biosynthesis of the above-described lipid mediators is generally difficult to confirm experimentally due to synthetic challenges and the labile nature of these epoxides that are very readily hydrolyzed. Despite these difficulties, the involvement of the 13S,14S epoxide precursor in the biosynthesis of MaRl (Figure 9.7) was recently demonstrated [22], Stereochemically pure 13S,14S epoxide, prepared via stereocontrolled total synthesis, upon incubation... 

Among new epoxides are two families containing fluorine and phosphorous, respectively. The fluoro-epoxides prepared by Griffith (76,77) at the Naval Research Laboratory have the following general structure ... 

An oxirane, also known as an epoxide (77), is a three-membered ring ether. The highly strained three-membered ring, analogous to a cyclopropane ring (Chapter 8, Section 8.5.3), makes an epoxide highly reactive. Contrary to most other ethers, they are easily opened by nucleophiles. How are epoxides prepared An important method for the preparation of epoxides is the oxidation of an alkene. 

Introduction to Ethers Nomenclature of Ethers Structure and Properties of Ethers Crown Ethers Preparation of Ethers Reactions of Ethers Nomenclature of Epoxides Preparation of Epoxides Enantioselective Epoxidation Ring-Opening Reactions of Epoxides Thiols and Sulfides... 

Taylor EC, Maiyanoff CA, Skotnicki JS (1980) Heterocychzation with cyano and sulfonyl epoxides. Preparation of quinoxalines and tetrahydroquinoxahnes. J Org Chem 45(12) 2512-2515. doi 10.1021/jo01300a053... 

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