Carbinols special

Toluene reacts with carbon monoxide and butene-1 under pressure in the presence of hydrogen fluoride and boron trifluoride to give 4-methyl-j iYbutyrophenone which is reduced to the carbinol and dehydrated to the olefin. The latter is cycHzed and dehydrogenated over a special alumina-supported catalyst to give pure 2,6- dim ethyl n aph th a1 en e, free from isomers. It is also possible to isomerize various dim ethyl n aph th a1 en es to the... 

The epoxidation of divinyl carbinol constitutes a special case of a dienol epoxida-tion, as the starting diene is not conjugated (Scheme 9.10). Desymmetrization by SAE, followed by a Payne rearrangement, furnishes the vinylepoxide in high yield and with excellent enantioselectivity (compare Table 9.2, Entry 1) [43]. 

The transformations of compounds which are precursors for vitamin A and carotenoids have a special position among the rearrangements of the conjugated polyenes. Numerous isomerizations such as cw-fraws-isomerization, the dehydration of polyunsaturated acetylenic carbinols etc. were utilized to prepare the various carotenoides (e.g. /1-carotene, lycopene, cryptoxanthin, zeaxanthin) (for reviews, see References 146 and 147). However, one of these rearrangements turned out to be a considerable hindrance for the synthesis of target products. 

Another successful example of such guest design is the Diels-Alder reaction markedly accelerated by the cyclodextrin inclusion. As shown in Table XXIV, /J-cyclodextrin accelerates the addition of a small dienophile to cyclopentadiene, but inhibits that of N-ethylmaleimide to anthracene-9-carbinol (117). Thus, the guest design is a really helpful concept for the remarkable catalysis. However, there seems to be some limitation in the choice of reactions, if cyclodextrins have no special functional group for the... 

To give an impression of the nature of useful experimental results, some flow birefringence measurements which were obtained on a solution of polystyrene in methyl 4-bromo-phenyl carbinol, are reproduced in Figs. 1.2 and 1.3. The concentration of the solution was 2 wt. percents, measuring temperatures are indicated in the figures. The special polystyrene used was a well-known sample of anionically polymerized polystyrene, viz. S 111, provided by the courtesy of Dow Chem. Corp. Its molecular weight is 224,000. The indicated solvent is, at 18 °C, a 0-solvent and possesses practically the same refractive index as polystyrene itself (32). The measurement results are kindly provided by Daum from his still unpublished work. 

In other special cases, cyclopropanones have been prepared by photochemical rearrangements. For example, 9,9 -dianthracyl ketone (27) 32> and carbinol (28) 33> undergo ring closure to their respective... 

Colorless derivatives of the carbinol bases of cationic dyes have recently found application for the manufacture of carbonless copy paper and for special paper used for thermal printers. Examples of such color formers are the crystal violet derivative 31 [29], which develops a blue color, and the black-developing fluorane lactone 32 [30] and benzoxazine 33 [31],... 

An enzyme involved in cell cycle control has been identified as the target of a compound supplied by broccoli, cabbage, and Brussels sprouts. One of the glucosinolates of these foods is the source of a chemical called indole-3-carbinol. Indole-3-carbinol enters the cell and influences the activity of a special protein kinase that is used to control the cell cycle. The chemical prevents the synthesis of the enzyme, and thus reduces its activity. The action of tins protein kinase (cyclin-dependent protein kinase 6) normally functions to make the cell embark on the Gi phase of the cell cycle, and thus to stimulate progression through the cell cycle. The chronic decrease in activity of this protein kinase serves to prevent cell division, but also prevents spontaneous cancers. The effect of indole-3-carbinol has been shown to occur in cultured cells, as well as in animals (Cover et al, 1998). 

Chiral malonate esters have been used successfully in asymmetric cyclopropanations, as shown by the example in Scheme 6.39, part of a total synthesis of steroids such as estrone [143,144]. The key step in this sequence is an intramolecular Sn2 alkylation of the monosubstituted malonate. The rationale for the diastereoselec-tivity is shown in the illustrated transition structure. Note that the enolate has C2 symmetry, so it doesn t matter which face of the enolate is considered. The illustrated conformation has the ester residues syn to the enolate oxygens to relieve Al>3 strain, with the enolate oxygens and the carbinol methines eclipsed. The allyl halide moiety is oriented away from the dimethylphenyl substituent, exposing the alkene Re face to the enolate. The crude selectivity is about 90% as determined by conversion to the dimethyl ester and comparison of optical rotations [143], but a single diastereomer may be isolated in 67% yield by preparative HPLC [144], This reaction deserves special note because it was conducted on a reasonably large scale ... 

Other synthetic reactions. Catalyzed elimination of allylic carbonates occurs in the absence of nucleophiles. Alkynediols undergo isomerization and dehydration, furnishing 2,5-disubstituted furans as a result. 1-Carboranyltributyltin adds to aldehydes under the influence of the Pd catalyst to form carbinols. The Pd version of a Pauson-Khand cyclopentenone synthesis is accomplishable in the presence of CO, and actually this version is specially suited for a one-step construction of a -methylenecyclopentenones. ... 

Occasionally, under special circumstances, the intermediate carbinols can be diverted to other products. For example with aryl benzyl ketones, dehydration occurs on reaction with POCI3 or on montmorillonite K-10 clay [126]. 

The pyrryl carbinols occupy a special place in synthetic pyrrole chemistry it was discovered early that with acid, they can react with another pyrrole nucleus to form the valuable dipyrrylmethane stmcture, which is of interest in the synthesis of porphyrins. Acid leads to the formation of the resonance stabilized pyrrylmethylcarbocation (7.2), which acts as an electrophile by the usual mechanism (Scheme 7.9). 

Cram s model does not always predict the stereochemical result of kinetically controlled reductions with aluminum isopropoxide (Cram and Greene, 1953). For example, i -(—)-3-cyclohexyl-2-butanone is reduced to predominantly ZR,2R-erythro carbinol (erythro/threo = 1.9). Apparently special steric forces are important in this reduction. Recent work (Shiner and Whittaker, 1963) has shown that aluminum isopropoxide is trimeric or tet-rameric. It is therefore conceivable that some hydride transfers will involve Al(OR)3 units that are not coordinated to the carbonyl groups they reduce. These transfers may occur preferentially from the side opposite that exposed to a coordinated Al(OR).3 unit. Such competitive mechanistic pathways might well yield an isomer ratio not in agreement with that produced by less complex reducing agents. 

Much of the work in this area has focussed on polymeric dyes which can participate in redox reactions. Early work by Manecke and Kossmehl on vinyl Malachite Green (VMG) is specially significant as it established a simple method of entry into the polymerizable triphenylmethane class of dyes. Thus the carbinol base form (ill) of VMG was synthesized by a Grignard reaction between vinyl-phenyl magnesium chloride (l) and Michler s ketone (ll). 

The acetaldehyde-TPP may then (1) split to yield acetaldehyde, (2) react with itself or a mole of free acetaldehyde to give the acyloin, acetylmethyl-carbinol (AMC), or (3) pass on the activated acetaldehyde molecule to a system which can oxidize it to a substance at the acid level of oxidation. In each case the TPP is made available for another catalytic cycle. The acetaldehyde-TPP intermediate has also been shown to be derived, in special instances, from free acetaldehyde and diacetyl. In some bacteria, the intermediate, derived from 1 mole of pyruvate, donates the acetaldehyde to a second mole of pyruvate to form acetolactic acid. The latter upon decarboxylation yields AMC. These reactions are pre-... 

---