Alcohol coupling

A valuable feature of the Nin/Crn-mediated Nozaki-Takai-Hiyama-Kishi coupling of vinyl iodides and aldehydes is that the stereochemistry of the vinyl iodide partner is reflected in the allylic alcohol coupling product, at least when disubstituted or trans tri-substituted vinyl iodides are employed.68 It is, therefore, imperative that the trans vinyl iodide stereochemistry in 159 be rigorously defined. Of the various ways in which this objective could be achieved, a regioselective syn addition of the Zr-H bond of Schwartz s reagent (Cp2ZrHCl) to the alkyne function in 165, followed by exposure of the resulting vinylzirconium species to iodine, seemed to constitute a distinctly direct solution to this important problem. Alkyne 165 could conceivably be derived in short order from compound 166, the projected product of an asymmetric crotylboration of achiral aldehyde 168. 

Allenic alcohols couple with allyl indium reagents at 140°C to give allylic alcohol products. Similarly, (o-hydroxy lactones couple with organoindium reagents. 

A wide variety of soUd acid catalysts has been examined using the methanol/isobutanol reaction mixture to establish activity and selectivity patterns for alcohol coupling and dehydration reactions (Table 1). 

Conclusive evidence has been presented that surface-catalyzed coupling of alcohols to ethers proceeds predominantly the S 2 pathway, in which product composition, oxygen retention, and chiral inversion is controlled 1 "competitive double parkir of reactant alcohols or by transition state shape selectivity. These two features afforded by the use of solid add catalysts result in selectivities that are superior to solution reactions. High resolution XPS data demonstrate that Brpnsted add centers activate the alcohols for ether synthesis over sulfonic add resins, and the reaction conditions in zeolites indicate that Brpnsted adds are active centers therein, too. Two different shape-selectivity effects on the alcohol coupling pathway were observed herein transition-state constraint in HZSM-5 and reactant approach constraint in H-mordenite. None of these effects is a molecular sieving of the reactant molecules in the main zeolite channels, as both methanol and isobutanol have dimensions smaller than the main channel diameters in ZSM-S and mordenite. 

Condensation of unsaturated alcohols with aldehydes. Homoallylic alcohols couple with aldehydes in the presence of A1C1, or AlBr, to form 4-halotetrahy-... 

An intriguing example of those enzymes that use both tyrosine residues and transition metal ions as partners in affecting redox chemistry is the fungal enzyme GO (GO EC 1.1.3.9 68 kD) (60,61,81), which catalyzes the two-electron oxidation of primary alcohols coupled to the two-electron reduction of O2 to H2O2, Eq. (2). 

Scheme 34 Alcohol coupling reactions by borrowing hydrogen...

A study on the combined use of a chiral substrate obtained by alcoholysis of a 4-benzylidene-5(4//)-oxazolone with a chiral alcohol coupled with hydrogenation using a chiral catalyst has also been described. This work shows that the matching effect of double asymmetric induction in hydrogenation can be modulated by a solvent effect. 

Exercise 15-27 A possible mechanism for producing esterification of an alcohol coupled with ATP hydrolysis would be the following ... 

Exercise 30-5 a. Nerol and geraniol cyclize under the influence of acid to yield a-terpineol. How could the relative ease of cyclization of these alcohols, coupled with other reactions, be used to establish the configurations atthe double bond of geraniol, nerol, geranial, and neral Write a mechanism for the cyclizations. 

The average relaxation time is of course temperature dependent and maybe related to a rate constant k for the relaxation process of the molecules in solution. Table 1.3 gives some representative data for EtOH and illustrates the extent to which the relaxation time decreases with temperature. It is noteworthy that the relaxation time decreases from 270 to 49 ps as the temperature rises from 10 to 70°C, and therefore, as the temperature increases the alcohol couples more effectively with the microwave source at 2.45 GHz. Such a situation is ripe for superheating the solvent, since the extent of conversion increases as the temperature rises. It also follows that some organic solvents with very long relaxation times at room temperature may appear to be unsuitable candidates for dielectric heating, but since the match becomes more favourable with temperature then they may behave as effective couplers as the temperature rises, that is, after a slow start they may very well heat very rapidly. 

Bicyetic acetals.5 Cyclic allylic alcohols couple with ethyl vinyl ether when treated with Pd(OAc)2. Only a catalytic amount of Pd(II) is required if Cu(OAc)2 is present as a reoxidant. The absence of double-bond isomerization is a useful feature of this coupling. 

Conventional industrial coatings materials of the thermoset type are usually acrylic, polyester, epoxy, polyurethane or silicone resins dispersed or dissolved in organic or water/ether-alcohol coupling solvents. They are cured with gas convection or electric IR ovens. The raw materials for the polymers come from petroleum feedstocks which are processed or manufactured into a finished coating system. 

The procedure for catalytic asymmetric epoxidation of allyl alcohol coupled with in situ derivatization involves the same methodology detailed above for ( )-2-octenol. On a 1.0 mol scale using ( + )-diisopropyl L-tartrate the reaction was complete in 6 hours at — 5°C. 

An alternative enzyme/transition metal combination employs transfer hydrogenation catalysts that are capable of racemizing secondary alcohols. The racemization procedure temporarily converts the alcohol into an achiral ketone, which is reduced back to the racemic alcohol. Coupling this racemization procedure to an enzyme-catalyzed acylation reaction affords a dynamic resolution process (Fig. 9-12). Several enzyme/transition metal combinations have been shown to be effective for these reactions, although ruthenium complexes 1-3 appear to be especially effective for the in situ racemization of the alcohol. The product esters are not prone to racemization under the reaction conditions. Early results employing transfer hydrogenation catalysts to effect the racemization of alcohols required the use of added ketone 21, 22. However, it was subsequently shown that added ketone was not required when appropriate transition metal complexes were used as catalysts. Furthermore, the use of 4-chlorophenyl acetate as the acyl donor afforded improved results. 

Figure 9-12. Transition metal-catalyzed racemization of alcohols coupled with enantioselective enzyme-catalyzed acetylation.

Phenyl-substituted propargyl alcohol couples with 3-iodopyridine to furnish (49) (Scheme 10). On reaction of the 2-iodopyridine (50), however, it was found that the initial alkynylation product (51) rearranged to form the corresponding chalcone (52). The same rearrangement occurs in pyrimidines when the iodine is located in an electrophilic position. In reactions with the corresponding methylpropargyl alcohol, the reaction stops after... 

The poor solvating property of t-butyl alcohol coupled with the strong basic properties of /-butoxide encourage a transition state with well-developed double-bond character and transition state I and to a lesser extent II are favoured. In the more solvating media, C -X bond breaking is depressed and a shift towards a carbanion-like E2 transition state is encouraged. Conforma-... 

The spectrum of neat ethanol is shown in Fig. 4.42(a). This spectmm was collected from a thin liquid film of ethanol between salt plates. The broad hydrogen-bonded OH stretch covers the region from 3100 to 3600 cm centered at about 3350 cm The strong C—C—O stretch at 1048 cm is characteristic of a primary alcohol. Coupling of the weak OH bend to the methylene bending mode and overlap of the methyl... 

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