Ethers preparation from epoxides

Allyl silanes react with epoxides, in the presence of Bp3 OEt2 to give 2-allyl alcohols.The reaction of a-bromo lactones and CH2=CHCH2Si(SiMe3)3 and AIBN leads to the a-allyl lactone.On the other hand, silyl epoxides have been prepared from epoxides via reaction with iec-butyllithium and chlorotri-methylsilane. ° a-Silyl-A-Boc-amines were prepared in a similar manner from the A-Boc-amine. " Arylsilanes were prepared by reaction of an aryl-lithium intermediate with TfOSi(OEt)3. In the presence of BEs etherate, allyl silane and a-methoxy A-Cbz amines were coupled. Benzyl silanes coupled with allyl silanes to give ArCHa—R derivatives in the presence of VO(OEt)Cl2 " and allyltin compounds couple with allyl silanes in the presence of SnCl4. Allyl silanes couple to the a-carbon of amines under photolysis conditions. 

Ether cross-linker Polyether CD-based polymers are mostly prepared from epoxides opening in basic conditions [7]. The most widely used epoxides are epichlorohydrin (EPI) and its nontoxic equivalent, the ethylene glycol diglycidyl ether (EGDE) (Scheme 2.3). 

To a mixture of 100 ml of THF and 0.10 mol of the epoxide (note 1) was added 0.5 g Of copper(I) bromide. A solution of phenylmagnesium bromide (prepared from 0.18 mol of bromobenzene, see Chapter II, Exp. 5) in 130 ml of THF was added drop-wise in 20 min at 20-30°C. After an additional 30 min the black reaction mixture was hydrolysed with a solution of 2 g of NaCN or KCN and 20 g of ammonium chloride in 150 ml of water. The aqueous layer was extracted three times with diethyl ether. The combined organic solutions were washed with water and dried over magnesium sulfate. The residue obtained after concentration of the solution in a water-pump vacuum was distilled through a short column, giving the allenic alcohol, b.p. 100°C/0.2 mmHg, n. 1.5705, in 75% yield. 

Easily prepared from the appropriate monosaccharide, a glycal is an unsatu-rated sugar with a C1-C2 double bond. To ready it for use in potysaccharide synthesis, the primary -OH group of the glycal is first protected at its primary -OH group by formation of a silvl ether (Section 17.8) and at its two adjacent secondary - OH groups by formation of a cyclic carbonate ester. Then, the protected glycal is epoxidized. 

Silyl enol ether 139 has also been transformed into D-allose, as shown in Scheme 5. The same methods can be applied to the enantiomeric enol ether derived from camphanate 38, and this allows one to prepare L-allose and its derivatives. Oxidation of 139 with MCPBA in THF (20 °C) led to the product of epoxide acidolysis 147 (69 %) which yielded 148 on heating to 200 °C for 15 min. Addition of 1.1 equiv. of MCPBA converted 148 into lactone 149 which in the presence of MeOH and K2CO3 (20 °C), gave selectively diester 150. Reactions 147... 

Aromatic Compounds.—A number of 2,3-dihydroxyoestra-l,3,5(10)-trienes have been prepared from the corresponding 2-amino-3-hydroxy-compounds using a novel inverse oxidation procedure followed by reduction with KI. Addition of the substrate to sodium metaperiodate in high dilution ensures no coupling with the intermediate quinonimines. 2-Bromo-oestradiol was readily converted into 2-methoxyoestradiol by treatment with NaOMe-MeOH-DMF-CuI. Novel preparations of the biologically interesting 11/3-methyl- and 11/3-ethyl-oestradiol have been reported in full. The key intermediates were the 11-oxo-oestradiol 3-benzyl ether (82) and its 9/3-epimer (83). The latter was derived from the 9,H-epoxides (81) by treatment with KOH followed by benzylation. The thermodynamically unstable 9a-epimer (82) was prepared from the 9j8-epimer (83) by... 

The azacrown ether-type chiral quaternary ammonium salts as chiral PTCs are easily prepared from BINOL in four steps. Remarkably, Table 6.10 shows that the good efficiency of asymmetric epoxidation of various chalcones can be achieved by adjustment of the length of the carbon chains on the nitrogen atom in the quaternary ammonium salts. 

The preparation of 1 started with the addition of lithiated 4 to the enantiomcrically-pure epoxide 5, which was prepared from the racemate using the Jacobsen protocol. Reduction followed by selective protection of the primary alcohol gave the monosilyl ether, which was further protected with MOM chloride to give 7. Pd-mediated oxidation to the methyl ketone followed by condensation with the Horner-Emmons reagent gave the unsaturated ester 8 as an inconsequential mixture of geometric isomers. Oxidation then set the stage for the crucial cyclization. 

R" may be alkyl or aryl. For dialkyl ethers, the reaction does not end as indicated above, since R OH is rapidly converted to R OR by the sulfonic acid (reaction 0-16), which in turn is further cleaved to R 0S02R" so that the product is a mixture of the two sulfonates. For aryl alkyl ethers, cleavage always takes place to give the phenol, which is not converted to the aryl ether under these conditions. Ethers can also be cleaved in a similar manner by mixed anhydrides of sulfonic and carboxylic acids733 (prepared as in 0-33). p-Hydroxy alkyl perchlorates734 and sulfonates can be obtained from epoxides.735 Epoxides and oxetanes give dinitrates when treated with N2Os,736 e.g.,... 

Again in the carbohydrate field, Raphael and Roxburgh14 4 described the preparation of a labile intermediate assumed to possess a monomeric epoxy ether structure but too reactive to allow its isolation. Unsuccessful attempts by Huffman and Tarbcll 48 to prepare an epoxide from 2-benzhydrylidenetotrahydrctfuran constitute additional evidence of the instability of bicyolio epoxy ethers. 

The current work on Friedel-Crafts polymerization of cyclic ethers may be considered to date from about 1940 when Meerwein and his associates prepared a series of tertiary oxonium salts and applied them to the polymerization of tetrahydrofuran. These salts, of the general form R30+... M X4i, are easily prepared from the corresponding metal halide in a reaction with an epoxide (preferably epichlorohydrin) in ether solution. According to Meerwein et al. (3) this reaction takes place in the following steps ... 

Selective epoxidation of the isolated double bond (Equation 35) in the ester 79, prepared from citronellal and triphenyl(ethoxycarbonylmethylene)phosphorane, followed by treatment with Na2PdCl4 and v/-butyl hydroperoxide gives the bis-ether 80 <1994CC903>. 

Epoxides (oxiranes) are three-membered cyclic ethers. The simplest and commercially most important example is ethylene oxide, manufactured from ethylene, air, and a silver catalyst. In the laboratory, epoxides are most commonly prepared from alkenes and organic peroxy acids. 

In many of the syntheses, aza-/3-lactam aldehyde 151 has been used as a key synthon (Scheme 20). For example, aldehyde 151 gives epoxide 157 by treatment with NaH and Me3S+I in DMSO at low temperature. Similarly, alcohol 156 may be prepared from 151 by reduction with LiAlH4 in ether. When NaBH4 is used in methanol a cyclic product 159 was isolated along with alcohol 158 (Scheme 20) <1998J(P1)2597>. 

Nitroperbenzoic acid has been used for the preparation of the epoxide (IK equation 42). In the aldehyde (115), the tetrasubstituted C(l)—C(2) double bond is not epoxidized since it is deactivated by conjugation with the aldehyde group. The disubstituted double bond is not sufficiently reactive due to the inductive effect of the allyl ether moieties. The epoxidation takes place from the a-face since the -face is blocked by the allylic substituents. The epoxide (116) cannot be prepared in satisfactory yields using MCPBA. 

Tri(organoseleno)boranes 35 are prepared from boron trihalides and organic selenolates as stable compounds (Scheme 35) [63]. These selenoboranes have been shown to be useful for the conversion of carbonyl compounds into seleno-acetals 36 [64] and the selective ring opening of epoxides [65]. Recently, it was reported that tri(phenylseleno)borane reacts with cyclic ethers to produce m-hydroxyalkyl phenyl selenides 37 in the presence of a catalytic amount of Lewis acid [43]. 

Racemic epoxy sulfone derivatives are easily prepared from al-lyl ethers by reaction with sodium p-toluenesulfinate in the presence of iodine followed by treatment with triethylamine, separation of E- and Z-isomers, and epoxidation with t-BuOOH and n-BuLi in THE (eq 3). ... 

Boron trifluoride-diethyl ether complex is a very versatile and useful Lewis acid in several organic reactions. The polymeric ether-BFs complex poly(p-methoxystyrene)-BF3 (14) has been prepared and is more stable and has higher activity in several organic reactions such as isomerization and epoxide rearrangement [26]. The polymeric version of pyridine-BF3 complex 15 has also been prepared from poly(vinylpyridine) and BF3 [27]. By analogy with the polystyrene-AlCls complex, simple crosslinked polystyrene also forms a stable complex in chloroform with boron trifluoride 16 [27]. 

The C23-C26 segment 173 was prepared from 180, which was derived from ribose (O Scheme 20). After 0-benzylation of 180, the resulting benzyl ether was treated with MeMgCl and CuBr Me2S to afford 181. Thiol acetal formation followed by selective silyla-tion provided 182. The dithioacetal was cleaved and the resulting aldehyde was reduced with NaBH4 to afford a diol, which was subjected to direct epoxidation to provide 173. 

The formation of aldehydes from 1,1-disubstituted epoxides has occasionally found use in synthesis, although simpler aldehydes in particular tend to form dioxolane dimers by BFs-induced reaction with epoxide. Hill et a converted the epoxide (94), which had been prepared from a 3-ionone derivative, into luciferin aldehyde (95) by treatment with cold BF3 etherate (equation 38). 

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