Carbinol intermediate

LTA4 was also synthesized by a three-component route to the oxiranyl carbinol intermediate (Ref. 7). 

The largest industrial use of LiC2H is in the production of vitamin A, where it effects ethynyl-ation of methyl vinyl ketone to produce a key tertiary carbinol intermediate. The acetylides and dicarbides of the other alkali metals are prepared similarly. It is not always necessary to prepare this type of compound in liquid ammonia and, indeed, further substitution to give the bright red perlithiopropyne Li4C3 can be effected in hexane under reflux ... 

Chloral condensations with aromatic hydrocarbons (and related derivatives) give rise to diaryltrichloroethane compounds, and are brought about in the presence of acid catalysts, proceeding with the formation of carbinol intermediates (Scheme 2.1). Commonly used catalysts include concentrated H2SO4 and its monohydrate, HCl, HF, I O,-, Lewis acids and a series of other acid agents [1, 2]. 

The Tschitschibabin reaction represents the most versatile way to substituted indolizines. It fails only in the case of indolizines bearing no substituents on the five-membered ring. Usually the intermediate quaternary salt (108) is isolated, but in some cases a one-pot reaction has been performed. The cyclization of (108) normally proceeds directly to the indolizine (110). A carbinol intermediate (109), however, has been isolated from the reaction of 2-picoline and 2-bromopropiophenone in the absence of a solvent (73JCS(P1)2595). 

Although the cyclization normally proceeds directly to the indolizine, the carbinol intermediate (1) was the product isolated when 2-picoline and 2-bromopropiophenone were heated together in the absence of a solvent.9 Usually the intermediate quaternary salt is isolated, but in some cases this is unnecessary and only the final product is isolated10,11 e.g., the base 2 in Eq. (1). A similar reaction, using an a-bromoester... 

For conversion of ketones into a,/3-unsaturated aldehydes containing two additional carbon atoms, several multistep processes via ethynyl or vinyl carbinol intermediates have been reported.4-10 Although the overall yields obtained by these routes for the conversion of cyclohexanone into cyclohexylideneacetaldehyde have never exceeded 50%, they were the only useful methods for this type of conversion until the excellent process of Wittig11 appeared. This process consists of normal aldol condensations of ketones with the lithium salt of ethylidenecyclohexylamine and subsequent dehydration and hydrolysis. 

The base used by Lee et al. (1977) and Coats (1983) was 1,5-diazabicyclo-[4.3.0] non-5-ene (DBN) numerous other bases have also been utilized, e.g., sodium methoxide, sodium bicarbonate, triethylamine, KOH, pyridine (Worrall, 1934 Hass et al., 1951 Kamlet, 1939). The carbinol intermediates were not purified prior to use in the condensation reaction. The acid used was a mixture of cone, sulfuric and glacial acetic acids (ratios ranged from 4 1 to 1 3). 

Hydroxyethylation of furfuryl alcohol with aqueous acetaldehyde was performed at 318 K in the presence of FAU, MOR and MFI zeolites in their protonic form. Besides the hydroxyethylation reaction, two other parallel reactions may compete, i.e. oligomerisation of acetaldehyde and resinification of furfuryl alcohol. The former reaction is easily controlled over a MFI catalyst with a Si/Al ratio of 25 but the latter is not, and linear furanic polymers, capable of deactivating the catalyst, were often formed. A selectivity of about 55 % in the carbinol intermediate was initially achieved in the presence of the MFI (25) catalyst for a furfuryl alcohol conversion up to 65 %. However, after optimization of the kinetic parameters, the selectivity is increased to 95 %, but to the detriment of furfuryl alcohol conversion. 

The acid-catalyzed alkylation of indoles by carbonyl compounds is complicated by the fact that the resulting indol-3-yl carbinols are usually reactive under these conditions. The most common outcome is the formation of W -indolylmethanes, as is discussed in the next section. In some cases, the carbinol intermediates can be diverted to alkylation by reductive trapping using triethylsilane-TFA. This reaction gives good yields of 3-benzyl indoles and there are a few examples of 3-alkylatiOTi using N-substituted indoles [120]. 

Tamura and colleagues generated an IQD (16) from 3-carboxy-l-methylindole-2-acetic anhydride by treatment with sodium hydride. Subsequent trapping with acetylenic dienophiles and a chloroquinone afforded the expected cycloadducts (Scheme 9, equation 1, and 17, 18) [65]. Ila, Junjappa, and coworkers also employed basic conditions to generate and trap a bright red IQD (19) from 1,2-dime-thyl-3-carboxyaldehyde (equation 2) [66]. A large number of carbazoles (20-22) and 1,2-dihydrocarbazoles (23-25) were synthesized in very good yields. Either silica gel or pyridinium tosylate was required to dehydrate/aromatize the initially formed carbinol intermediate. 

The entrapped combined Pd-[Rh(cod)Cl]2 catalyst was shown to promote also direct reductive conversion of benzylic ketones into hydrocarbons without passing through carbinol intermediates (Scheme 24-40) (Abu-Reziq, 2002b). 

Ninhydrin in acetic acid also forms carbinol intermediates with pyrroles. These are converted by stronger acids into blue compounds (33). 

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