Alcohols target

Retrosynthetic strategies, limited to the more obvious but widely used FGI and disconnection transforms in the case of an allylic alcohol target molecule, are summarised below. 

Tables 2.2, 2.3, 2.4, 2.5, 2.6, 2002 illicit drug use and alcohol target achieved for...

Alcohols are extremely versatile starting materials for organic synthesis, since they can be converted to a wide variety of functional groups. Many simple alcohols are commercially available, but this section will focus on the preparation of alcohols. These synthetic strategies will be useful not only for complex alcohol target molecules (TMs), but also for alcohols that may be intermediates within a larger synthesis. 

This then is the disconnection corresponding to the reaction. It is the thinking device we use to help us work out a synthesis of t-butyl alcohol. We could of course have broken any other bond in the target molecule such as ... 

Since (A) does not contain any other functional group in addition to the formyl group, one may predict that suitable reaction conditions could be found for all conversions into (A). Many other alternative target molecules can, of course, be formulated. The reduction of (H), for example, may require introduction of a protecting group, e.g. acetal formation. The industrial synthesis of (A) is based upon the oxidation of (E) since 3-methylbutanol (isoamyl alcohol) is a cheap distillation product from alcoholic fermentation ( fusel oils ). The second step of our simple antithetic analysis — systematic disconnection — will now be exemplified with all target molecules of the scheme above. For the sake of brevity we shall omit the syn-thons and indicate only the reagents and reaction conditions. 

Usually there is little advantage in choosing one route over another to prepare a particular target alcohol For example all three of the following combinations have been used to prepare the tertiary alcohol 2 phenyl 2 butanol... 

Several other biosensors have been developed usiag this oxygen-quenched fluorescence approach. Target species iaclude ethanol [64-17-5] hydrogen peroxide [7722-84-17, H2O2, lactate, and xanthine [69-89-6] C H4N402, usiag alcohol oxidase, catalase [9001-05-2] lactate oxidase, and xanthine oxidase, respectively. An additional technique for biocatalytic biosensors iavolves the firefly chemiluminescent reaction (17) ... 

Cychc alcohols are excellent targets for enantioselective enzymatic acylations. For example, acylation of (65) with vinyl acetate catalyzed by Hpase SAM-II gives the (R),(3)-ester with 95% ee (81). Similarly (66), which is a precursor for seratonin uptake inhibitor, is resolved in a high yield and selectivity with Amano Hpase P (82). The prostaglandin synthon (67) is resolved by the same method into the optically pure alcohol in 35% yield (83). 

Dipolar cydoadditions are one of the most useful synthetic methods to make stereochemically defined five-membered heterocydes. Although a variety of dia-stereoselective 1,3-dipolar cydoadditions have been well developed, enantioselec-tive versions are still limited [29]. Nitrones are important 1,3-dipoles that have been the target of catalyzed enantioselective reactions [66]. Three different approaches to catalyzed enantioselective reactions have been taken (1) activation of electron-defident alkenes by a chiral Lewis acid [23-26, 32-34, 67], (2) activation of nitrones in the reaction with ketene acetals [30, 31], and (3) coordination of both nitrones and allylic alcohols on a chiral catalyst [20]. Among these approaches, the dipole/HOMO-controlled reactions of electron-deficient alkenes are especially promising because a variety of combinations between chiral Lewis acids and electron-deficient alkenes have been well investigated in the study of catalyzed enantioselective Diels-Alder reactions. Enantioselectivities in catalyzed nitrone cydoadditions sometimes exceed 90% ee, but the efficiency of catalytic loading remains insufficient. 

Identify the target alcohol as primary, secondary, or tertiary. A primary alcohol can be prepared by reduction of an aldehyde, an ester, or a carboxylic acid a secondary alcohol can be prepared by reduction of a ketone and a tertiary alcohol can t be prepared by reduction. 

Cyciization processes involve ring-closure of amino alcohols (Scheme 4.3) or equivalents, and as the aziridine precursors are often available as single stereoisomers, the method is an attractive one if the aziridine target is a key synthetic intermediate. 

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