Reduction and Elimination Reactions

Fujitsu, E. Matsumura, S. Shirahama, K. Takeshita, and I. Mochida, J. Chem. Soc., Perkin Trans. 1, 1982, 855. 

Reduction and Elimination Reactions of Oxirans.—New and simple methods for the deoxygenation of epoxides to alkenes have been reported.Treatment of epoxides [146 R = octyl, H, decyl, or Me R = H, octyl, or Me R = octyl, tridecyl, or MeO(CH2)8 or R R = (CH2),u, R = H or Me] with P2I4, PI3, or MeSil affords a conversion into alkenes that is 100% stereoselective. P2I4 has also been used in the deoxygenation of (146 R = heptyl, R = R = R = H) and (146 R = R = Ph, R = R = H), in 92% and 70% yields, to their respective alkenes. The stereochemistry of each epoxide appears to be retained in the alkene products. 

The zerovalent titanium bis(benzene) complex (147) has been found to deoxygenate propene oxide efficiently in THF, at 80 °C, to propene (100%) in 2 hours. 

Derguini-Boumechal, and G. Linstrumelle, Tetrahedron Lett., 1979, 1503. J. P. Marino and D. M. Floyd, Tetrahedron Lett., 1979, 675. 

The reduction of /Sy-epoxy-sulphones has been used as a new synthesis of a-methylene-carbinols. The epoxy-sulphone (153), prepared from 1-cyclo-hexenylmethanol, was reductively eliminated by Na(Hg) in THF-MeOH to methylenecyclohexanol (154). The same reduction/elimination procedure comprises part of that for a general synthetic sequence of allylic alcohols (156 R ,R, R = H or Me, R = hexyl), via )3y-epoxy-sulphones (155), in 60—90% yields. Any group R may be introduced by alkylation of (155 R = H). 

A preliminary report on asymmetric induction in the formation of cyclohex-2-enol from cyclohexene oxide has appeared. Using chiral lithium amide bases, 

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The metabolism of neonicotinoids in vertebrates, insects, and plants has many common features. It may result in cleavage and the separation of the heterocyclic and pharmacophore moieties, or modifications of a pharmacophore in an intact parent molecule. Oxidations, reductions, and elimination reactions are the major mechanisms that result mostly in a reduced or diminished insecticidal potency of the metabolites. Dehydration of the 4-hydroxyimidazolidinyl resulting in a formation of the imidazolinyl (olefin) or reduction of the N-nitroimine ( = N—NO2) to N-nitrosoimine ( = N—NO) group (Figure 5) are examples of a... 

Fission of the ring of cyclohexa-1,4-diene carboxylate (or possibly also the cyclohex-1-enecarboxylate) by a series of hydroxylation, and reductive and elimination reactions to produce 3-hydroxyp-imelate (or pimelate) that then enters the metabolic system. 

Electrophilic Opening 20 Nucleophilic Opening 22 Cyclisation Reactions 26 Reduction and Elimination Reactions 28 Photochemical Reactions 30 Reactions with Organometallic Compounds 30 Miscellaneous Reactions 34... 

Reduction and Elimination Reactions. A new procedure for the reduction of epoxides has been reported in which the epoxide is heated with NaBH in a Me,COH-MeOH mixture by this method styrene oxide gave PhCH(0H)Me as the major product together with PhCH2CH20H. Asymmetric reduction of... 

In Robinson s now well-known suggestions, regarding the processes by which alkaloids may be produced in plants, two main reactions are used j the aldol condensation and the similar condensation of carbinol-amines, resulting from the combination of an aldehyde or ketone with ammonia or an amine, and containing the group. C(OH). N., with substances in which the group, CH. CO. is present. By these reactions it is possible to form the alkaloid skeleton, and the further necessary changes postulated include oxidations or reductions and elimination of water for the formation of an aromatic nucleus or of an ethylene derivative. 

Formation of C—Nu The second mode of nucleophilic addition, which often occurs with amine nucleophiles, involves elimination of oxygen and formation of a C=Nu bond. For example, aldehydes and ketones react with primary amines, RNH2, to form imines, R2C=NR. These reactions proceed through exactly the same kind of tetrahedral intermediate as that formed during hydride reduction and Grignard reaction, but the initially formed alkoxide ion is not isolated. Instead, it is protonated and then loses water to form an imine, as shown in Figure 3. 

The phase-transfer catalysis method has also been utilized effectively for addition of dichlorocarbene to olefins,4 as well as for substitution and elimination reactions, oxidations, and reductions.18 The preceding procedure in this volume is another example.13... 

Considerable attention has been directed to dehalogenation mediated by corrinoids and porphyrins in the presence of a chemical reductant (references in Gantzer and Wackett 1991 Glod et al. 1997 Workman et al. 1997). Illustrations are provided by the dechlorination and elimination reactions carried out by titanium(III) citrate and hydroxocobala-min (Bosma et al. 1988 Glod et al. 1997). The involvement of corrinoids and porphyrins is consistent with the occurrence of analogous mechanisms for biological reactions that... 

Insertion of CO into the metal-methyl bond of 1 followed by reduction and elimination of water would yield a metal ethyl species (3). This latter set of reactions represents, formally at least, a possible growth sequence for the Fischer-Tropsch synthesis. 

In this section, you were introduced to some of the main types of organic reactions addition, substitution, and elimination reactions oxidation and reduction and condensation and hydrolysis reactions. In the next section, you will take a close look at each type of reaction. You will find out how organic compounds, such as alcohols and carboxylic acids, can react in several different ways. 

The reduction of adenine (267) is suggested to follow420 a similar route rather than that described in Part I, and that purine is formed after the first two-electron reduction and elimination of ammonia. A similar route is possibly followed in the deamination of 7-amino-6-phenylpyrazolo[l,5-a]-pyrimidine.351 Reduction followed by elimination is probably the most general reaction path for removing substituents bound to a heterocyclic ring through O, N, or S. 

Analogous reactions are given by the minor radical cation [reactions (16) and (17)], and the secondary C(4 ) radicals can eliminate the other phosphate such as reaction (18) that is shown here as an example. Reduction and oxidation reactions depicted as examples in reactions (20) and (12) lead after release of unaltered bases [reactions (13) and (21)] to a series of dideoxypentoses and C(4 ) keto products, free and bound to DNA (Beesk et al. 1979 for the determination of these products see Chap. 13.2). 

Number of Carbohydrate and Selected Amino Acid Residues per Mole of Glucoamylase before and after Alkaline Reductive /3-Elimination Reaction... 

The coupling of j8-bromostyrene with lithium diorganocuprates at a low temperature was also accompanied by reduction and elimination as important side reactions (309). The reaction is summarized by Eq. (54). 

More recently Sternberg (8) has studied the dissolution of coal by reductive alkylation, which Involves a variety of reactions, Including free radical and elimination reactions. 

Reactions may be grouped into substitution, elimination, addition, oxidation, reduction and rearrangement reactions. 

Nucleophilic Substitution Solvolytic and Elimination Reactions Ring-opening of Epoxides Esters, Ethers, and Related Derivatives of Alcohols Oxidation Reduction Miscellaneous... 

Now the alkene must be moved yet one more time around the ring to prepare the way for another intramolecular Heck reaction. Hydroboration (chapter 17) of 153 is regioselective because of the large N-Boc group and Swem oxidation completes the insertion of the ketone 155. Reduction and elimination use another palladium-catalysed reaction. Conversion to the triflate 157 is followed by Pd-catalysed transfer hydrogenation, the H atom coming from formic acid HC02H. 

It is often assumed that the electron donors improve stereoselectivity by selectively complexing atactic sites on the catalyst surface. This may be the mechanism with simple electron donors such as tertiary amines. However, in contrast, esters undergo irreversible reactions with AIR3 under polymerization conditions (Scheme 1). Reactions are complex and consecutive steps involving alkylation, reduction, and elimination can lead to many products. Although third components, e.g., esters, are very effective selectivity control agents, they also greatly depress catalyst activity and increase catalyst decay rate (Table 1, 14.5.3.3). 

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