Anionic epoxides

A great variety of aromatic diamines and aliphatic di- and poly-amines are used as epoxy resin curing agents, and tert-amines can act as catalysts for anionic epoxide homopolymerisation. 

Another important asymmetric epoxidation of a conjugated systems is the reaction of alkenes with polyleucine, DBU and urea H2O2, giving an epoxy-carbonyl compound with good enantioselectivity. The hydroperoxide anion epoxidation of conjugated carbonyl compounds with a polyamino acid, such as poly-L-alanine or poly-L-leucine is known as the Julia—Colonna epoxidation Epoxidation of conjugated ketones to give nonracemic epoxy-ketones was done with aq. NaOCl and a Cinchona alkaloid derivative as catalyst. A triphasic phase-transfer catalysis protocol has also been developed. p-Peptides have been used as catalysts in this reaction. ... 

After workup with ammonium chloride (liberation of NH3 and NaCl) and extraction with hot dimethylsulfoxide products 4 and 5 can be isolated as white solids in yields of ca. 30 %. The low yield of the desired product observed for the epoxide addition reaction is attributed to an anionic epoxide polymerisation process [5],... 

B.iii. Julia-Colonna Epoxidation. A new and useful innovation involving the hydroperoxide anion epoxidation of conjugated carbonyl compounds modified the procedure so the reaction is done in the... 

Anionic Epoxide Polymerization Initiated by Alkali Metal Derivatives... 

Anionic Epoxide Poiymerization initiated by Alkaii iWetai Derivatives... 

A different strategy to the above vinyl anion -epoxide approaches to homo-allylic alcohols involves allyl anion (or equivalent) additions to carbonyl groups. A new method for the addition of allyl silanes to aldehydes and ketones (Scheme 21)... 

In addition, polymers with free carboxylic acid groups such as PAA and poly(methacrylic acid) can form copolymer electrolytes with PEO, leading to a sharp increase in ionic conductivity. Apparently, the PAA or other polycarboxylic acids can increase the lithium-ion transference number by decreasing the transfer of anions. The ionic conductivities of these copolymer electrolytes can be further increased by adding boron trifluoride diethyl etherate (Bp30Et2), which can promote the dissolution of lithium cations and carboxylic acid anions. Epoxidized natural rubber can also increase the ionic conductivity of PEO. Addition of symmetric poly(styrene-Wocfc-ethylene oxide) copolymers obviously affects the distribution of Lb ions. In contrast to current solid and liquid electrolytes, its ionic conductivity increases with increasing molecular weight of the copolymers. 

The proton of terminal acetylenes is acidic (pKa= 25), thus they can be deprotonated to give acetylide anions which can undergo substitution reactions with alkyl halides, carbonyls, epoxides, etc. to give other acetylenes. 

The obvious disconnection gives an epoxide and an enolate anion ... 

Since epoxides are attacked by anions at the less substituted carbon atom, we shall be able to make B but not A, so we continue. 

Epoxides provide another useful a -synthon. Nucleophilic ring opening with dianions of carboxylic acids (P.L. Creger, 1972) leads to y-hydroxy carboxylic acids or y-lactones. Addition of imidoester anions to epoxides yields y-hydroxyaldehyde derivatives after reduction (H.W. Adickes, 1969). 

Silyl ethers serve as preeursors of nucleophiles and liberate a nucleophilic alkoxide by desilylation with a chloride anion generated from CCI4 under the reaction conditions described before[124]. Rapid intramolecular stereoselective reaction of an alcohol with a vinyloxirane has been observed in dichloro-methane when an alkoxide is generated by desilylation of the silyl ether 340 with TBAF. The cis- and tru/u-pyranopyran systems 341 and 342 can be prepared selectively from the trans- and c/.y-epoxides 340, respectively. The reaction is applicable to the preparation of 1,2-diol systems[209]. The method is useful for the enantioselective synthesis of the AB ring fragment of gambier-toxin[210]. Similarly, tributyltin alkoxides as nucleophiles are used for the preparation of allyl alkyl ethers[211]. 

Nucleophiles other than Gngnard reagents also open epoxide rings These reac tions are carried out in two different ways The first (Section 16 12) involves anionic nucleophiles in neutral or basic solution... 

There is an important difference in the regiochemistry of ring opening reactions of epoxides depending on the reaction conditions Unsymmetncally substituted epoxides tend to react with anionic nucleophiles at the less hindered carbon of the ring Under conditions of acid catalysis however the more highly substituted carbon is attacked... 

Section 16 12 Anionic nucleophiles usually attack the less substituted carbon of the epoxide m an 8 2 like fashion... 

Monomers which can be polymerized with aromatic radical anions include styrenes, dienes, epoxides, and cyclosiloxanes. Aromatic radical anions... 

Alkoxide-Type Initiators. Using the guide that an appropriate initiator should have approximately the same stmcture and reactivity as the propagating anionic species (see Table 1), alkoxide, thioalkoxide, carboxylate, and sUanolate salts would be expected to be usehil initiators for the anionic polymeri2ation of epoxides, thikanes, lactones, and sUoxanes, respectively (106—108). Thus low molecular weight poly(ethylene oxide) can be prepared... 

Propylene oxide and other epoxides polymerize by ring opening to form polyether stmctures. Either the methine, CH—O, or the methylene, CH2—O, bonds ate broken in this reaction. If the epoxide is unsymmetrical (as is PO) then three regioisomers are possible head-to-tad (H—T), head-to-head (H—H), and tad-to-tad (T—T) dyads, ie, two monomer units shown as a sequence. The anionic and... 

Polymerization to Polyether Polyols. The addition polymerization of propylene oxide to form polyether polyols is very important commercially. Polyols are made by addition of epoxides to initiators, ie, compounds that contain an active hydrogen, such as alcohols or amines. The polymerization occurs with either anionic (base) or cationic (acidic) catalysis. The base catalysis is preferred commercially (25,27). 

Electron deficient carbon-carbon double bonds are resistant to attack by the electrophilic reagents of Section 5.05.4.2.2(t), and are usually converted to oxiranes by nucleophilic oxidants. The most widely used of these is the hydroperoxide ion (Scheme 79). Since epoxidation by hydroperoxide ion proceeds through an intermediate ct-carbonyl anion, the reaction of acyclic alkenes is not necessarily stereospecific (Scheme 80) (unlike the case of epoxidation with electrophilic agents (Section 5.05.4.2.2(f)) the stereochemical aspects of this and other epoxidations are reviewed at length in (B-73MI50500)). 

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