Reactions with epoxides secondary alkyl

The carboxymethylation of sucrose can be achieved by reaction with sodium chloroacetate in water or water-2-propanol mixtures in basic medium. In this case, a similar regioselectivity is observed as for the reaction with epoxides or alkyl halides with major substitutions at secondary positions, notably at OH-2.80 Cyanoethylated sucrose derivatives and the corresponding carboxylated compounds were also prepared.81... 

Hydride ion will remove a proton from the OH group, forming a good nucleophile that can react with the secondary alkyl halide in an 8 2 reaction to form an epoxide. An 8 2 reaction requires back-side attack. Only when the alkoxide ion and Br are on opposite sides of the cyclohexane ring will the alkoxide ion be able to attack the back side of the carbon that is attached to Br. Therefore, only the trans isomer will be able to form an epoxide. 

Benzyl methyl ether or allyl methyl ethers can be selectively metalated at the benzylic/allylic position by treatment with BuLi or sBuLi in THF at -40 °C to -80 C, and the resulting organolithium compounds react with primary and secondary alkyl halides, epoxides, aldehydes, or other electrophiles to yield the expected products [187, 252, 253]. With allyl ethers mixtures of a- and y-alkylated products can result [254], but transmetalation of the lithiated allyl ethers with indium yields y-metalated enol ethers, which are attacked by electrophiles at the a position (Scheme 5.29). Ethers with ft hydrogen usually undergo rapid elimination when treated with strong bases, and cannot be readily C-alkylated (last reaction, Scheme 5.29). Metalation of benzyl ethers at room temperature can also lead to metalation of the arene [255] (Section 5.3.11) or to Wittig rearrangement [256]. Epoxides have been lithiated and silylated by treatment with sBuLi at -90 °C in the presence of a diamine and a silyl chloride [257]. 

The key step in all these transformations is without doubt the reaction of l-lithio-l,3-dithianes with organic halides and epoxides. The alkylation usually proceeds extremely rapidly with primary alkyl iodides (-78 C, 0.2 h) and with allylic and benzylic halides - - (Scheme 59, entry a) but is much slower with secondary alkyl iodides and bromides. The reaction is best carried out at low temperature in order to obtain good yields by lowering the competitive elimination reaction it has been found to proceed with inversion of the configuration at the asymmetric carbon when optically active alkyl halides are used. ... 

Compared with several synthetically important anions, ester enolates are rather poor nucleophiles in conversions with alkyl halides and epoxides [4], reactions that have a relatively high activation energy barrier. Yields of the alkylation products are often rather low (especially in reactions with secondary alkyl bromides and iodides) due to the occurrence of condensation of the alkylation product with unreacted enolate. Improved results in alkylations may be obtained when using the very polar DMSO or HMPT as co-solvent [1] under these conditions only C-alkylation products are formed. 

The reaction of epoxides or episulfides with trialkyl phosphites containing one or more secondary or tertiary alkyl groups is reported to give mainly phosphonates rather than olefins and phosphates (287). Evidently, in this case nucleophilic attack of the phosphorus reagent on carbon takes place. 

A more efficient and more generahy applicable cobalt-catalysed Mizoroki-Heck-type reaction with aliphatic halides was elegantly developed by Oshima and coworkers. A catalytic system comprising C0CI2 (62), l,6-bis(diphenylphosphino)hexane (dpph 73)) and Mc3 SiCH2MgCl (74) allowed for intermolecular subshtution reactions of alkenes with primary, secondary and tertiary alkyl hahdes (Scheme 10.25) [51, 53]. The protocol was subsequently applied to a cobalt-catalysed synthesis of homocinnamyl alcohols starting from epoxides and styrene (2) [54]. 

The alkyl radical formed in the initial oxidation reactions subsequently react with O2 resulting in the formation of alkylperoxy radical. The alkylperoxy radical is the key intermediate in the oxidation of VOCs by OH radical and further reacts with HO2, NO2 and NO in the atmosphere. This intermediate can also undergo self-reaction and epoxidation reactions. These reactions lead to the formation of hydroperoxide adducts, alkoxy radical and O3, and also OH radical regeneration. The alkoxy radical is the second key intermediate in the VOCs oxidation by OH radical. The alkoxy radical undergoes prompt decomposition resulting in the oxidation of NO. The characterization of these secondary reactions is studied extensively using theoretical methods, but only very few experimental studies are available for such reactions. 

---