Aldol route

Parent poly(thienylene vinylene) has also been synthesized by an aldol precursor route [122]. In this method, 5-methyl-2-thiophenecarbaldehyde 76 is treated with a base and the monomer polymerizes yielding a precursor 77 which is soluble in water. Thermal treatment in an acidic solution at 80 °C yields the fully conjugated material. Alternatively, the solid polymer may be heated to 280 °C to effect elimination of water. Fully conjugated material exhibits low conductivity (10 S cm ) in its pristine state. 

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Branched-Chain Carboxylic Acids. Branched-chain acids such as 2-methylbutyric, 3-methylbutyric, isooctanoic, and isononanoic acids are produced by the oxo reaction, giving first the corresponding aldehyde, which is then oxidized to the acid. 2-EthyIhexanoic acid is produced by the aldol route from butyaldehyde in three steps aldol condensation hydrogenation of the carbon—carbon double bond and oxidation of the branched-chain saturated aldehyde to 2-ethyIhexanoic acid (see Carboxylic Acids, branched-chain acids). 

A Stable Class of Low-Band-Gap Materials 24 Organic Field Effect Transistors (FETs) 25 Synthesis 26 Aldol Route 27... 

SCHEME 11. Synthesis of prostaglandins and analogues by the aldol route. 

Thus, the aldol route will be blocked, or partially blocked, if the only available aldehydes have fewer than two C-hydrogens. Hence, inclusion of "blocking" aldehydes of Group 1 or 2 in a browning reaction mixture should increase the proportion of free aldehyde produced and generally lower the chain length of aldol polymers formed. Overall, an increase in aroma volatiles should be observed, except with aldehydes of such low boiling point as to be able to escape physically and for which the aldol condensation acts as a restraint. 

A simple pyrrolidine imide (10), derived from L-proline, brings about the direct formation of a -unsaturated ketones from unmodified ketones and aldehydes under mild conditions.31 Mechanistic investigation suggests a Mannich elimination process, rather than an aldol route. 

Di-2-ethylhexyl phthalate (DOP) had already been patented as a composition of matter and examples of its use as a plasticizer for cellulosics, etc., but not PVC, were cited(2). However, it was not until later in the decade that the overall advantages of DOP were recognized. This was a key factor in the large scale production of 2-ethylhexanol (2EH) by Union Carbide Corp. starting in 1939(3), followed shortly by the commercialization of DOP — also by Union Carbide(4). 2-Ethylhexanol was made at that time via the "double aldol" route, starting with acetaldehyde. 

While n-butanol from the oxo process did not become a major intermediate for PVC plasticizers, the development was nonetheless a breakthrough of far-reaching significance. The precursor of n-butanol in the oxo process is n-butyraldehyde. This made possible the manufacture of 2-ethylhexanol by "single aldol" at lower cost than the "double aldol" route via acetaldehyde. 

Scheme 17 Intramolecular aldol route to the welwistatin core...

Scheme 9. Ghosh s asymmetric anh-aldol route to bis-THF alcohol 11.

The oxo-HDA reaction of 2-carbonyl derivatives of pyridine 1-oxide with electron-rich dienes catalysed by bisoxazoline Cu(II) complexes proceeds by a Mukaiyama-aldol route and affords dihydropyran-4-ones 33 in good yield and excellent enantioselectivity <07JOC240>. 

An aldol route was rather adopted by Kishi [139,140] for the construction of the central unit of trimer analogs 346-353 of the type 11(H) cellular antigen trisaccharide a-L-Fuc-(1 2)-... 

Like /3-hydroxyaldehydes and -ketones, jS-hydroxyesters and -acids are readily dehydrated. The unsaturated compounds thus obtained (chiefly a,]3-unsaturated) can be hydrogenated to saturated carboxylic acids. Extended in this way, the Reformatsky reaction is a useful general method for preparing carboxylic acids, paralleling the aldol route to alcohols. 

The future of the commercial acetaldehyde processes mainly depends on the availability of cheap ethylene. Acetaldehyde has been replaced as a precursor for 2-ethylhexanol ( aldol route ) or acetic acid (via oxidation cf. Sections 2.1.2.1 and 2.4.4). New processes for the manufacture of acetic acid are the Monsanto process (carbonylation of methanol, cf. Section 2.1.2.1), the Showa Denko one-step gas-phase oxidation of ethylene with a Pd-heteropolyacid catalyst [75, 76], and Wacker butene oxidation [77]. Other outlets for acetaldehyde such as pentaerythritol and pyridines cannot fill the large world production capacities. Only the present low price of ethylene keeps the Wacker process still attractive. 

In Thaurea aromatica, phenylalanine was found to be converted to benzoyl-CoA by an anaerobic a-oxidation route via phenylpyruvate and phenylacetate [route 4 on Figure 3, (iP)]. Further, a non-oxi tive, retro-aldol route to benzoyl-CoA via benzaldehyde was also described in plants (route S on Figure 3). Feeding these intermediates to our engineered S. lividans strains did not lead to the production of soraphen A (Table I), indicating that neither of these two metabolic routes are operational in this host under the tested conditions. 

The Synthesis of Enones by Many Strategies Introduction to the various strategies Strategy 4a The Aldol Route to Enones... 

The true product is the 1,3-diol 191, of which the product actually formed 190 is the formaldehyde acetal, and the disconnection should be contrasted with the aldol route 192 to the same product as a different carbon-carbon bond is formed. 

QM/MM calculation on the MPS- catalyzed reaction suggested that the transition state of the two-step Micheal-aldol route is more stable than that of the concerted Diels-Alder route, indicating that the two-step route is an energetically preferred process. To evaluate the validity of the calculation results, experimental evidence must he provided. A recent finding that the first decarboxylation, the second C—C bond formation, and the third decarboxylation to 151 are rapid processes, suggested that it is difficult to distinguish between... 

On the basis of the data available so far it looks as if this process is well suited for the single-step production of alcohols but less suited if aldehydes are the desired reaction products, which is the case in the 2-ethylhexanol manufacture and similar aldol routes, in the manufacture of carboxylic acids and some other operations (as to the possibility of making a certain amount of aldol product along with the lower molecular alcohols in the Shell process, see chapter 7). 

Especially in the range of Cg-Ci3 the 0x0 route holds the dominating position since the other routes, like the aldol route starting from acetaldehyde, the hydrogenation of fatty acid esters or the Ziegler alcohol route, can hardly compete pricewise [342, 899]. 

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