Aldehyde Homologation

Petroski, R. J. and Bartelt, R.J. (2007). Direct aldehyde homologation utilized to construct a conjugated-tetraene hydrocarbon insect pheromone. J. Agric. Food Chem., 55, 2282-2287. 

Action of Chlorine upon the Aldehydes, Aldehydes homologous with ordinary aldehyde, as well as those analogous to hydruret of benzoyl, when submitted to the action of chlorine, lose hydrogen, with equivalent substitution only. Thus ordinary aldehyde produces successively... 

CHO group attached to benzene ring, first member of aromatic aldehyde homologous series... 

By reacting 1,4-butane diol with paraformaldehyde in the presence of sulfuric acid at 150-180" , the seven-membered 1,3-dioxepane is prepared. With other aldehydes, homologous 2-alkyl-substituted 1,3-dioxepanes have also been prepared using a cationic ion exchange resin instead of sulfuric acid. This latter technique was introduced by Astle [42]. The dioxepanes have been converted to polymers in methylene dichloride or in 1,2-dichloro-ethylene. The initiator used was boron trifluoride etherate the reaction temperatures ranged from -10° to +10°. The reactions were carried out under anhydrous conditions by techniques suitable for reaction kinetics studies. The work indicated that, at least for this class of compounds, the polymerization propagation step involves linear alkoxycarbenium ions [47]. 

The mechanism of the aldehyde homologation is predicted to occur through a multistep process that consists of the concerted formation of an A-thiazolium 2-yUde intermediate (10), followed by nucleophilic addition of this intermediate to another aldehyde molecule (11). Loss of the first aldehyde gives the addition product (eq 20). The observation of the spiro(thiazoline-2,4 -dioxolane) (12) by NMR in a kinetic study provides additional evidence for this mechanism. The conversion of compound 12 into the final product should proceed through the loss of two molecules of aldehyde and the transfer of the silyl group to the oxygen atom in the C-2-alkyl moiety. 

A new -arylethylamine synthesis by aryl aldehyde homologation has also been developed. A procedure has been found for the specific ortho alkylation of aromatic amines.A review of the use of quaternary ammonium compounds in organic synthesis has recently appeared. Mannich bases may be prepared regiospeclfically using the reaction of enol borates with dimethyl (methylene)-ammonium iodide. A very complete review of... 

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