Alcohols alkene synthesis

Alkene synthesis via alcohol dehydration is complicated by carbocation rearrangements A less stable carbocation can rearrange to a more sta ble one by an alkyl group migration or by a hydride shift opening the possibility for alkene formation from two different carbocations... 

Chiral active pharmaceutical ingredients, 18 725-726. See also Enantio- entries Chiral additives, 6 75—79 Chiral alcohols, synthesis of, 13 667-668 P-Chiral alcohols, synthesis of, 13 669 Chiral alkanes, synthesis of, 13 668-669 Chiral alkenes, synthesis of, 13 668—669 Chiral alkoxides, 26 929 Chiral alkynes, synthesis of, 13 668-669 Chiral ammonium ions, enantiomer recognition properties for, 16 790 Chiral ansa-metallocenes, 16 90 Chiral auxiliaries, in oxazolidinone formation, 17 738—739... 

Methanol can then be used as a starting material for the synthesis of alkenes, aromatic compounds, acetic acid, formaldehyde, and ethyl alcohol (ethanol). Synthesis gas can also be nsed to produce methane, or synthetic natrrral gas (SNG) (Demirbas, 2007) ... 

In combination with the range of standard transformations of alcohols, alkenes, and vinylsulfides, these silicon-tethered additions of functionalized radicals offer a versatile and stereoselective approach to amino alcohol synthesis. Whereas vinyl and 2-oxoethyl radicals have not yet been demonstrated as competent participants in the various intermolecular additions reported in the literature, the temporary tether approach allows such functionalized fragments to be installed in an efficient and stereoselective manner. Synthesis of the aminosugar daunosamine from achiral precursors shows how this concept, employing hydrazone radical acceptors, can be merged with asymmetric catalysis to achieve practical synthetic advances. 

Adenosine 5 -(tr1hydrogen diphosphate), 5 5 ester with 3-(ami nocarbonyl)-alcohol dehydrogenase, 63, 17 Adogen 464 [50934-77-5], 60, 11 Alanine, L-, N-carboxybenzyl ester, 63, 182 ALANINE, PHENYL-, N-tert-BUTOXYCARBONYL-, L-, 63, 160 Alanine, N-[(phenylmethoxy)carbonylL- [1142-20-7], 63, 182 Alcohols, alkynyl-, synthesis of, 63, 61 Alcohols, amino-, by reduction of acids, 63, 138 Aldol condensation, intramolecular, asymmetric, 63, 26, 37 Aldol condensation, diastereoselectlve, 63, 94, 104 ALIPHATIC B-KETOESTERS, 61, 5 Alkene photodimerization, 62, 125... 

The Wittig alkenation has found widespread application in synthetic organic chemistry, and numerous papers and reviews have detailed the progress of the Wittig reaction. A principal advantage of alkene synthesis by the Wittig reaction is that the location of the double bond is absolutely fixed in contrast to the mixture often produced by alcohol dehydration. With simple substituted ylides Z-alkenes are favoured. 

The products of this reaction, an equimolar mixture of H2 and CO (called synthesis gas or syn gas some CO2 may be produced as a by-product), can be used with metallic heterogeneous catalysts in the synthesis of a variety of useful organic products. For example, the Fischer-Tropsch process, developed by German chemists in the early 1900s, uses transition metal catalysts to prepare hydrocarbons, alcohols, alkenes, and... 

The combination of reactions described above (Sections 2.6.4.2 to 2.6.4.5) allows the selective synthesis of a large variety of alcohols, allyl alcohols, alkenes, epoxides and carbonyl compounds from p-hydroxyalkyl selenides. These products often can be obtained from two ca nyl compounds by activation of one of them as an a-selenoalkyllithium (Schemes 161-196). 

Another interesting alkene synthesis starts from a cyclopropyl-substituted alcohol, which, on reaction with magnesium halides, is converted to a haloalkene MesSiX has also been used in this type of reaction (Scheme 22). ... 

Ito et al. have reported that a sequence of intramolecular hydrosilylation or cya-nosilylation and the Pd-catalyzed coupling reaction is useful for regio- and stereo-defined synthesis of tri- or tetrasubstituted homoallyl alcohols from homopropargyl alcohols (Scheme 10.212) [551, 552]. More recently Denmark et al. have used ring-closing metathesis for the alkene synthesis via vinylsilanes [553]. 

We return to two compounds we made earlier by the AE reaction propranolol 7 and diltiazem 67. In both cases the synthesis is easier as we do not have to start with an allylic alcohol. The synthesis of propranolol41 uses the allyl ether 188 that gives the diol 189 with good ee in the AD reaction for a monosubstituted alkene. Transformation to the epoxide 190 shows no loss of ee. Reaction with /-Pi NIE was already known to give propranolol 7. This is a very short synthesis from easily made starting materials. 

Acidic clays are widely applied in the dehydration of alcohols [38]. Although similar to zeolites in their capacity to induce the formation of both alkenes and ethers, selective alkene synthesis is possible. Various layered materials (clays, ion-exchanged montmorillonite, pillared layered clays) are very active and, in general, selective in transforming primary, secondary, and tertiary aliphatic alcohols to 1-alkenes [39-43]. Al -exchanged montmorillonite, however, induces ether formation from primary alcohols and 2-propanol [41]. Substituted 1-phenyl-1-ethanols yield the corresponding styrene derivatives at high temperature (653-673 K) [44]. 

Epoxide opening. A stereoselective alkene synthesis starts from reaction of triethylsilyloxirane with an organocuprate reagent, and it is concluded by oxidation of the j8-silyl alcohol to the aldehyde, Grignard reaction and elimination of [Et Si/OH]. The elimination leads to either the ( )- or the (Z)-alkene by using different reagents. 

One other experimental result from the Corey et al. study is important for trisubstituted alkene synthesis. When 55=58 is quenched with formaldehyde, the stereochemistry of C—C bond formation remains the same as before. However, the regiochemistry of the elimination step no longer favors the second aldehyde added, and the major product is now the allylic alcohol 64 (54). This experiment suggests that both oxaphosphetanes 63 and 62 are in equilibrium with the lithium halide adduct 61a. Decomposition is controlled by the nature and degree of oxaphosphetane substitution as well as by stereochemistry. In the formaldehyde reaction, these factors combine to favor the trisubstituted alkene (via 62) over the disubstituted alkene that would be formed via 63 (R"=H). Several examples of trisubstituted alkene synthesis using Corey s method are summarized in Table 10 without further comment because the origins of stereochemistry are not understood in detail, but Corey s model 58 is consistent with the available evidence. 

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