Alcohols preparation from aldehydes

Scheme 6.151 Range of allylic alcohols prepared from 145-catalyzed MBH reactions of2-cyclohexene-l-one with various aldehydes.

I -Bromo-1 -alkettes.1 These products can be prepared from aldehydes or ketones by a two-step process addition of dibromomethyllithium (prepared in situ) to form dibromo alcohols, followed by reduction with zinc dust and acetic acid in refluxing methylene chloride. The method is particularly useful for preparation of 1-bromo-l, 3-dienes. The only drawback is the lack of stereoselectivity. 

Indium trichloride promotes catalytically the addition of alkynylstannanes to aldehydes (Table 25).42 Metallic indium also mediates the same Barbier-type coupling between alkynyl halides and aldehydes or ketones to give secondary or tertiary propargyl alcohols (Table 26). Secondary alcohols can be oxidized in situ according an Oppenauer process.395 Thus, alkynyl ketones have been prepared from aldehydes via an indium-mediated alkynylation reaction followed by an indium-mediated Oppenauer oxidation. They are also obtained via an indium-mediated alkynylation of the relevant acyl chlorides (Table 27).396... 

Secondary and tertiary alcohols can be prepared from aldehydes and ketones, respectively, by means of zinc alkyls (403) or the compounds formed from the alkyl halides and magnesium. This latter method was investigated by Grignard. As has already been pointed out, when magnesium is added to a solution of an alkyl halide in ether or other appropriate solvent, the metal and the halide unite and form an addition-product —... 

These reactions are not limited to the simple oxazine and oxazolines described above. They are readily prepared from aldehydes and amino alcohols. Meyers used this methodology to prepare chiral precursors for use in asymmetric synthesis. When keto-acid 299 was treated with valinol (300), chiral bicyclic lactam 301 was... 

A new simple synthetic route to 2,5-dihydrooxazoles 71 by cycloaddition of allyl azido ethers 70 via triazoUnes was shown by Hassner et al. [37]. Earlier, they demonstrated that cr-azido ethers can be easily prepared from aldehydes using an alcohol, hydrazoic acid and titanium tetracliloride as well as the fact that thermolysis of azido ethers in the absence of a double bond forms imi-dates [35,36]. Using the above mentioned facts, the allyl azido ethers 70 were synthesized in good yields employing an aldehyde, an allyl alcohol and HN3 in a 1 3 9 ratio in presence of a Ti catalyst (Scheme 12). Allyl azido ethers 70, on thermolysis in benzene, proved to be ideal substrates for the formation of 2,5-dihydrooxazoles 71 in 66-90% yield. To show that oxazolines are formed via triazolines and not via an independent nitrene pathway, thermolysis of 70 was followed by NMR in hexadeuteriobenzene at 70 °C. 

Arylmethylamines can be oxidized to the corresponding arylamides by formation of a Schiff base with 2,6-di-t-butylbenzoquinone and base-catalysed oxygenation. Allenic alcohols are oxidized to allenic amides by nickel peroxide at -20 °C in ethereal ammonia. N-Alkyl-amides can be prepared from aldehydes in a four-step procedure consisting of imine formation and subsequent reactions with N-chlorosuccinimide, potassium cyanide, and finally alcoholic HCl. ... 

Dess-Martin oxidation of alcohol III-26 gave aldehyde III-27, which was used in the next step without further purification. Aldehyde III-27 reacted with the Bestmann-Ohira reagent [96-101] to give alkyne III-28, from which alkynylindole III-29 was obtained by Boc cleavage after a brief exposure to trifluoroacetic acid. This four step procedure can be routinely carried out without purification of any intermediate in 14—23 % overall yield. Alternatively, alkyne III-29 could be prepared from aldehyde III-27 by the Corey-Fuchs procedure, although the overall yield was lower using this procedure [102],... 

Alcohols may also be prepared from aldehydes by some of the methods listed in section 42 (Alcohols and Phenols from Ketones)... 

Alcohols are prepared from aldehydes and 2° alcohols are from ketones. 

The Dess-Martin periodinane ( DMP ) reagent, U,l-tris(acetyloxy)-l,l-dihydro-l,2-benziodoxol-3(l//)-one, has also been used in several complex syntheses for the oxidation of primary or secondary alcohols to aldehydes or ketones, respectively (e.g., M. Nakatsuka, 1990). It is prepared from 2-iodobenzoic add by oxidation with bromic add and acetylation (D.a Dess, 1983). 

The thermal glass-transition temperatures of poly(vinyl acetal)s can be determined by dynamic mechanical analysis, differential scanning calorimetry, and nmr techniques (31). The thermal glass-transition temperature of poly(vinyl acetal) resins prepared from aliphatic aldehydes can be estimated from empirical relationships such as equation 1 where OH and OAc are the weight percent of vinyl alcohol and vinyl acetate units and C is the number of carbons in the chain derived from the aldehyde. The symbols with subscripts are the corresponding values for a standard (s) resin with known parameters (32). The formula accurately predicts that resin T increases as vinyl alcohol content increases, and decreases as vinyl acetate content and aldehyde carbon chain length increases. 

Mixtures of anhydrous hydrogen fluoride and tetrahydrofuran are successfully used as fluorinating agents to convert 1,1,2-trifluoro-l-allcen-3-ols, easily prepared from bromotrifluoroethene via lithiation followed by the reaction with aldehydes or ketones, to 1,1,1,2-tetrafluoro-2-alkenes The yields are optimal with a 5 1 ratio of hydrogen fluoride to tetrahydrofuran The fluorination reaction involves a fluonde lon-induced rearrangement (Sf,j2 mechanism) of allylic alcohols [65] (equation 40)... 

Section 15.2 Alcohols can be prepared from car bonyl compounds by reduction of aldehydes and ketones. See Table 15.3. 

The carboranyl alcohol can also be prepared from the stannyl carborane and an aldehyde using Pd2(dba)3-CHCl3/dppe. The carborane is stable to Brpnsted and Lewis acids and to LiAlH.. 

The oxazoloquinolinequinone derivative 610 was prepared from the allylphenol 605 which was transformed to the alcohol 606 and then to the aldehyde 607. Subsequent debenzylation gave 608 that was oxidized with Ce(NH4)2(N02)6 to the quinone 609 that upon cyclization with ethanolamine gave the oxazoloquinolinequinone 610 which showed... 

Alcohols occupy a central position in organic chemistry. They can be prepared from many other kinds of compounds (alkenes.. alkyl halides, ketones, esters, and aldehydes, among others), and they can be transformed into an equally wide assortment of compounds (Figure 17.3). 

Primary alcohols are oxidized to either aldehydes or carboxylic acids, depending on the reagents chosen and the conditions used. One of the best methods for preparing an aldehyde from a primary alcohol on a small laboratory scale, as opposed to a large industrial scale, is to use pyridinium chloro-chromate (PCC, CsH NCrO Cl) in dichloromethane solvent. 

Epoxides from aldehydes, 46, 44 Equatorial alcohols, preparation by use of the lithium aluminum hydride-aluminum chloride reagent, 47, 19... 

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