Epoxides intramolecular reaction

The titanium-catalyzed AE reaction is a fairly robust system and it can be performed on substrates containing a wide range of different functional groups (FGs) (Table 6.3) [13]. However, it is important to point out that an intramolecular reaction with the formed epoxide is possible whenever the FG present in the molecule has a favorable position to facilitate such a transformation. An illustration of this phenomenon is presented in Eq. (1) [28]. 

We have observed intramolecular reactions of septanose species under a variety of reaction conditions using a number of starting materials. Figure 10 shows the putative reactive intermediates 190-193 that were present during iodoglycosidation of the D-xylose-derived oxepine 143, epoxidation of the oxepine 142, and TMS-triflate activation of septanosyl fluorides 72 and 75, respectively. Products 194-197 were obtained in a range of yields depending on whether or not other nucleophiles were present in the reaction. All of the intermediates are electrophilic and therefore... 

According to the Baldwin rule, the exo cyclization mode is favored in intramolecular reactions of alkynyloxiranes with alcohols to afford cyclic ethers. However, the unfavorable endo cyclization mode is observed by the complexation. Thus exclusive endo cyclization of epoxide complex 146 takes place regioselectively to give 147, without forming the five-membered ether 148 by exo mode reaction [37]. 

Alkyl halides (particularly bromides) undergo oxidative addition with activated copper powder, prepared from Cu(I) salts with lithium naphthalenide, to give alkylcopper species10. The alkyl halides may be functionalized with ester, nitrile and chloro functions ketone and epoxide functions may also be tolerated in some cases11. The resulting alkylcopper species have been shown to react efficiently with acid chlorides, enones (conjugate addition) and (less efficiently) with primary alkyl iodides and allylic and benzylic bromides (equations 5 and 6). If a suitable ring size can be made, intramolecular reactions with epoxides and ketones are realized. 

Carbon-oxygen bonds can also be formed by the intramolecular reaction between an alkyne and an epoxide using 5 mol% AUCI3 in acetonitrile 20,21... 

Treatment of certain 2-(hydroxymethyl)aziridines with base can lead to an intramolecular ring-opening reaction to yield an cc-amino epoxide, a reaction analogous to the Payne rearrangement of (hydroxymethyl)epoxides. For example, treatment of the aziridine 109 with potassium tert-butoxide provides the epoxide 110 in good yield. 

A second example of an intramolecular reaction of a vinyl epoxide with an electron rich aromatic ring provides an exceptional yield of benzazepine 29 <07TL8558>. This reaction provides the azepine ring in 91% yield. It is quite remarkable that none of the 6-membered ring was formed in the cyclization. 

The intermediate resulting from addition of H is similar to the intermediate in a Williamson ether synthesis. Intramolecular reaction occurs to form the epoxide. 

Treatment of the acid (67a) with carbonyldiimidazole and 90% H2O2 furnishes the epoxide (67b equation 44). This reaction is more than 100 times faster than the epoxidation of (67a) with MCPBA (see equation 26). It has been suggested that under the experimental conditions of equation (44) the acid (67a R = OH) is transformed to the peroxy acid (67a R = O2H), which reacts regio- and stereo-selec-tively through an intramolecular reaction. 

An intramolecular reaction of epoxides promoted by a titanium halide which is somewhat different from simple opening of an epoxide with a nucleophile is shown in Eq. (290) [654]. The starting epoxide was first attacked by a bromide ligand of TiBr4, in an intermolecular manner, and this was followed by the intramolecular attack of... 

The second case involves an intramolecular Sn2 reaction by a sulfur anion on one end of (h epoxide. The reaction occurs stereospecificaUy with inversion and so one enantiomer of oi diastereoisomer of the product is formed. Some redrawing is needed and we have kept the epoxide of the starting material in its original position to avoid mistakes. 

Cyclic phosphonate analogues of PMEA (36) have been obtained after stereoselective cyclisation of an acyclic phosphonyl intermediate to the phos-phonyltetrahydrofuran nucleoside derivative. A series of cyclopropylphos-phonate analogues (37) has been synthesised stereoselectively via intramolecular epoxide opening reaction of y,5-epoxyalkanephosphonates with subsequent Mitsunobu coupling reaction to purine bases. Acyclic phosphonate derivatives of thymine (38-43) have been prepared and evaluated as multisubstrate analogue inhibitors of Escherichia coli thymidine phosphor-... 

As is the case with hydrolysis of epoxidised vegetable oils, by alcoholysis the hydroxyl numbers obtained are always lower than theoretically expected. The explanation is the same the intermolecular and intramolecular reactions between the formed hydroxyl groups and the unreacted epoxidic rings. These reactions conserve the number of hydroxyl groups and do not generate new hydroxyl groups. By intramolecular reactions dimers and trimers of lower hydroxyl number and higher functionality are formed. 

Organocopper reagents can be made directly from the bromides and active Cu, which is prepared by reduction of CuCN nLiX with lithium naphthalenide. Copper prepared from Cul PR, (R=Bu, Ph) is most suitable for intramolecular reaction of bromoaryl epoxides to give dihydrobenzofurans. 

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