Epoxy ethers reduction

Reduction of, (t-epoxy alcohols. Reduction of 3-substituted-2,3-epoxy alcohols by SMEAH, particularly in THF, gives essentially only the 1,3-diol. However, a substituent at C2 reverses the selectivity and decreases the reaction rate. The hydroxyl group also plays a role the corresponding benzyl ethers show only a slight preference for reduction at C3.1... 

With chiral catalyst 47d regioselective reductive ring opening reactions of racemic epoxides can be achieved, For alkynyl epoxy ethers it leads to effective asymmetric 5-exo cyclization of one radical, but reduction of the other [161, 162]. 

Scheme 2 Reaction of epoxy ethers 3 with secondary amines and reduction.

So, we were able to prepare selectively syn and anti trifluoromethyl amino alcohols. The next step was a search for a chiral approach to these compounds. Two approaches have been investigated to obtain chiral anti amino alcohols first we performed the reaction of epoxy ethers 3 with the chiral dimethylaluminum amide, prepared from the fi -phenethylamine and MeaAl (Scheme 5). From 3a, the reaction was effective leading, after reduction to the anti diastereoisomers 8a and 9a stereoselectively (Scheme 5). However, the chiral amine induced no selectivity anti amino alcohols 8a and 9a were obtained in a 50/50 mixture. Their separation was performed by crystallisation of the mandelate salts. Although this access to homochiral anti amino alcohols is somehow tedious, it is general since oxirane ring opening is efficient whatever the R substituent, and since epoxy ethers, substituted with various fluoroalkyl groups, are available. ... 

Reaction of 10a and 11a with the aluminum amide prepared from MejAl and the (R)-phenethylamine and subsequent reduction step occurred with the same excellent anti/syn diastereoselection as precedently, leading respectively to anti amino alcohols 8a and 9a. These amino alcohols were obtained in an excellent purity from 10a (8a/9a = 93/7) and from 11a (9a/8a = 90/10). The stereoisomeric excess is the same as the enantiomeric excess of starting epoxy ethers. No racemization occurred in the reaction ring opening does not involve a carbenium ion, and no enolization occurs from intermediate A or B. Both enantiommc amino alcohols 12a and 13a were obtained by debenzylation with palladium hydroxide imfortunately, we have not been able to assign the absolute configuration of the asymmetric carbons of 8a and 9a (Scheme 7). 

Rearrangement of a,/B-epoxy ketones to ftdicarbonyl isomers, 307 Reductive alkylation, 97 Reductive cleavage of halo ethers, 264 Reductive degradation of 19-substitutional steroids, 277, 278 Reformatsky reaction, 139 Removal of the C-10 substituent in steroids. 272... 

The synthesis of the trisubstituted cyclohexane sector 160 commences with the preparation of optically active (/ )-2-cyclohexen-l-ol (199) (see Scheme 49). To accomplish this objective, the decision was made to utilize the powerful catalytic asymmetric reduction process developed by Corey and his colleagues at Harvard.83 Treatment of 2-bromocyclohexenone (196) with BH3 SMe2 in the presence of 5 mol % of oxazaborolidine 197 provides enantiomeri-cally enriched allylic alcohol 198 (99% yield, 96% ee). Reductive cleavage of the C-Br bond in 198 with lithium metal in terf-butyl alcohol and THF then provides optically active (/ )-2-cyclo-hexen-l-ol (199). When the latter substance is treated with wCPBA, a hydroxyl-directed Henbest epoxidation84 takes place to give an epoxy alcohol which can subsequently be protected in the form of a benzyl ether (see 175) under standard conditions. 

Recently, results of careful experiments were reported by Ito et a/.101 They claimed that formic acid, formaldehyde, and methanol, which had been previously reported as photoelectrochemical reduction products of carbon dioxide, were observed also by photolysis of cell materials, such as electrolytes, including 15-crown-5 ether, and epoxy resin, which has often been used as the molding material of semiconductor electrodes in aqueous solutions. Previously reported reduction products were obtained also under nitrogen with (Table 4) and without (Table 5) a p-GaP photocathode under illumination. These precise experiments under improved conditions, where no photolytic products were observed, gave the result that the main reduction product of carbon dioxide at a p-GaP photocathode in aqueous electrolytes was formic acid. Thus, many kinds of products reported in previous papers83,97,100 were suggested to be due to photolysis of cell materials. 

The sesquiterpene skeleton has also been assembled by the intramolecular nitrile oxide cycloaddition sequence. Oxime 238 (obtained from epoxy silyl ether 237), on treatment with sodium hypochlorite gave isoxazoline 239, which was sequentially hydrolyzed and then subjected to the reductive hydrolysis conditions-cyclization sequence to give the furan derivative 240 (330) (Scheme 6.93). In three additional steps, compound 240 was converted to 241. This structure contains the C11-C21 segment of the furanoterpene ent-242, that could be obtained after several more steps (330). 

Reduction of ttjl-epoxy ketones. These ketones arc reduced with high stereoselectivity to err/Aw-epoxy alcohols ( > 90% erythro) by Zn(Blt4), in ether, regardless... 

FIGURE 1.5 Viscosity reduction of a diglycidyl ether of bisphenol A (DGEBA) epoxy resin by reactive diluents.31... 

Zinc borohydride was effective for the reduction of a,P-epoxy ketones (49) to the corresponding anti-a,3-epoxy alcohols (50) in ether at 0 °C irrespective of the substituents on the epoxide (equation 14). The selectivity was rationalized by intramolecular hydride delivery from a five-membered zinc chelate avoiding the epoxide ring. In a limited study of the stereoselective reduction of y,8-epoxy ketones (51), LAH and di-2-(o-toluidinomethyl)pyrrolidine in ether at -78 C gave the desired c/j-epoxy alcohols (52) required for ionophore synthesis with good selectivity (>10 1) (equation 15). ... 

Tetranortriterpenoids.—The structure of sendanin (72), from the bark of a Japanese variety of Melia azedarach, has been confirmed by AT-ray analysis. The novel enol-ether (73) has been isolated from the heartwood of Khaya anthotheca along with 11/3- and lla-acetoxyazadirone (74) and (75). Zinc-copper couple is a very convenient reagent for reduction of epoxides, a,/S-epoxy-lactones, a/S-unsaturated ketones, and a-ketols. The full details of the X-ray analysis of prieurianin have appeared. " ... 

Aryl ethyl ethers are deethylai exposure to microwaves in the pres of selectivity by the addition of eth Palladium halide complexed to haloarenes with powdered NaCN ii Olefiturtions. Vinylogation 1,3-dioxolan-2-ylmethyltriphen> Ipl feasible. Similarly, asymmetric Ej been induced by RbOH in the pte Oxidations and reductions. benzylamines to benzamides with aldehydes can be carried out in tolu Epoxidation of various alken phase-transfer conditions using so economical and environmentally I a,P-epoxy ketones are deoxj H,NC(=NH)SO,H under phase-tnu... 

The presence of a functional group in the vicinity of the epoxide can lead to interesting results. Such is the case for the epoxy-2,3 alcohols 2.23, which can be obtained in a nonracemic form by asymmetric epoxidation of the corresponding allylic alcohols [KS3]. The action of LAH in THF or better yet of Red-Al in the same solvent [MM2, VI] or preferably in DME [GS4] selectively leads to the 1,3-diols 2.24, while DIBAH [FKl] or LiBH4-(i-PrO)4Ti in [DLl] gives access to the 1,2-diols 2.25 (Figure 2.15). The hydride attack is stereospecific, and in the nonracemic chiral molecule 2.26, the reaction proceeds with inversion [FKl] (Figure 2.15). If the alcohol residue is transformed into a methyl ether, Red-Al does not promote any reduction [FKl]. 

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