Alcohols acyclic

The thermolysis of xanthates derived from primary alcohols yields one olefin only. With xanthates from secondary alcohols (acyclic or alicyclic) regioisomeric products as well as fi/Z-isomers may be obtained see below. While acyclic substrates may give rise to a mixture of olefins, the formation of products from alicyclic substrates often is determined by the stereochemical requirements the /3-hydrogen and the xanthate moiety must be syn to each other in order to eliminate via a cyclic transition state. 

Stereoselective hydroboration of allylic alcohols. Acyclic secondary ally lie alcohols of the types 1 and (E)- and (Z)-2 undergo hydroboration stereoselectively to yield threo-, 3-dioh (3). Highest t/ireo-selectivity in hydroboration of 1 is obtained using 9-... 

The Polyhydric Alcohols Acyclic Polyhydric Alcohols, E. J. Bourne, in Handbuch der Pflanzenphysiologie, W. Ruhland, ed., Springer Verlag, Berlin, 1958, pp. 345-362. 

Polyprenols, polyprenyl alcohols acyclic, polyiso-prenoid alcohols. P. occur free or esterified with higher fatty acids in microorganisms, plants and animals. The natural source and the number of isoprene units is usually indicated in the names of P., e. g. betulapie-nol-8 is formed from 8 isoprene units and is found in Betula verrucosa. 

For example, when an N-methylthioacetamide (96), R, = R — Me, was condensed with chloroacetone, a 2,3,4-trimethylthiazolium chloride was obtained in quantitative yield. The reaction is usually run in aqueous or alcoholic solution at room temperature. At low temperature, with N-phenylthioacetamide (96), Rj = Me, R2 = Ph and chloroacetone, an acyclic intermediate (98) was isolated and characterized (Scheme 43). It was easily converted to 2,4-dimethyl-3-phenylthiazolium chloride (97), R, = Rs = Me, Rj -Ph, by heating (99,102, 145). 

But the reaction with aliphatic a-halocarbonyl compounds is usually complex, and a variety of compounds can be formed depending on the reactants and the reaction conditions. With chloroacetone in neutral medium (alcohol) the acyclic intermediate (144) analogous to those obtained with thiourea and thioamides was isolated (Scheme 70). 

Thus the reactions of cyclic or acyclic enamines with acrylic esters or acrylonitrile can be directed to the exclusive formation of monoalkylated ketones (3,294-301). The corresponding enolate anion alkylations lead preferentially to di- or higher-alkylation products. However, by proper choice of reaction conditions, enamines can also be used for the preferential formation of higher alkylation products, if these are desired. Such reactions are valuable in the a substitution of aldehydes, which undergo self-condensation in base-catalyzed reactions (117,118). Monoalkylation products are favored in nonhydroxylic solvents such as benzene or dioxane, whereas dialkylation products can be obtained in hydroxylic solvents such as methanol. The difference in products can be ascribed to the differing fates of an initially formed zwitterionic intermediate. Collapse to a cyclobutane takes place in a nonprotonic solvent, whereas protonation on the newly introduced substitutent and deprotonation of the imonium salt, in alcohol, leads to a new enamine available for further substitution. 

For the construction of oxygen-functionalized Diels-Alder products, Narasaka and coworkers employed the 3-borylpropenoic acid derivative in place of 3-(3-acet-oxypropenoyl)oxazolidinone, which is a poor dienophile in the chiral titanium-catalyzed reaction (Scheme 1.55, Table 1.24). 3-(3-Borylpropenoyl)oxazolidinones react smoothly with acyclic dienes to give the cycloadducts in high optical purity [43]. The boryl group was converted to an hydroxyl group stereospecifically by oxidation, and the alcohol obtained was used as the key intermediate in a total synthesis of (-i-)-paniculide A [44] (Scheme 1.56). 

The rearrangement with ring contraction probably is the most important synthetic application of the Favorskii reaction it is for example used in the synthesis of steroids. Yields can vary from good to moderate. As solvents diethyl ether or alcohols are often used. With acyclic a-halo ketones bearing voluminous substituents in a -position, yields can be low a tcrt-butyl substituent will prevent the rearrangement. 

It is important to note that the one-step conversion of 27 to 28 (Scheme 4) not only facilitates purification, but also allows differentiation of the two carbonyl groups. After hydrogenolysis of the iV-benzyl group (see 28—>29), solvolysis of the -lactone-ring in 29 with benzyl alcohol and a catalytic amount of acetic acid at 70 °C provides a 3 1 equilibrium mixture of acyclic ester 30 and starting lactone 29. Compound 30 can be obtained in pure form simply by washing the solid mixture with isopropanol the material in the filtrate can be resubjected to the solvolysis reaction. 

The C2-symmetric epoxide 23 (Scheme 7) reacts smoothly with carbon nucleophiles. For example, treatment of 23 with lithium dimethylcuprate proceeds with inversion of configuration, resulting in the formation of alcohol 28. An important consequence of the C2 symmetry of 23 is that the attack of the organometallic reagent upon either one of the two epoxide carbons produces the same product. After simultaneous hydrogenolysis of the two benzyl ethers in 28, protection of the 1,2-diol as an acetonide ring can be easily achieved by the use of 2,2-dimethoxypropane and camphor-sulfonic acid (CSA). It is necessary to briefly expose the crude product from the latter reaction to methanol and CSA so that the mixed acyclic ketal can be cleaved (see 29—>30). Oxidation of alcohol 30 with pyridinium chlorochromate (PCC) provides alde-... 

Andersson also showed that, in addition to meso-desymmetrization, kinetic resolution of some cyclic epoxides by use of the first-generation catalyst was also possible, giving both epoxides and allylic alcohols in good yields (Scheme 7.51) [108], Kozmin reported the effective use of the same catalyst in the desymmetrization of diphenylsilacyclopentene oxide. The resulting products could be used in the ster-eocontrolled syntheses of various acyclic polyols (Scheme 7.52) [109]. 

For acyclic systems, the anti diastereoselectivity of the (i )-enolates is lower than the syn diastereoselectivity of comparable (Z)-enolates. For example, carboxylic acid esters, which form predominantly ( )-enolates, react with aldehydes with high anti selectivity only in those cases where bulky aromatic substituents are in the alcoholic part of the ester22 25. 

Direct alkylation of allylic alcohols via the (allyloxy)phosphonium ion intermediate normally proceeds with anti-y selectivity for the Cyclic system, and sy/i-y selectivity for the acyclic system (see Table l)35 36. 

Whereas acyclic sulfoxides form complexes with various metal salts, thiirane oxides react with copper(II) chloride or bromide163 in benzene at room temperature to give the thiolsulfonate 146a. In alcoholic solution below 0 °C the major products are sulfinates (149). Similar results are obtained in the reaction of thiirane oxides with ethanesulfinyl chloride163 as summarized in equation 60. 

Intramolecular Hydrogen Bonding in Some Acyclic Alcohols, A. B. Foster, A. H. Haines, and M. Stacey. Tetrahedron, 16(1961) 177-184. 

Both cyclic and acyclic allylic cations have been produced in this way. Stable allylic cations have also been obtained by the reaction between alkyl halides, alcohols, or alkenes (by hydride extraction) and SbFs in SO2 or S02C1F. Divinylmethyl... 

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