Submitted to: Synthetic Communications
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/13/2011
Publication Date: 6/17/2011
Citation: Petroski, R.J., Vermillion, K. 2011. Two-carbon homologation of aldehydes and ketones to a,beta-unsaturated aldehydes. Synthetic Communications. 16:5062-5078. Interpretive Summary: The study of insect chemical ecology requires the synthetic preparation of insect pheromones, some having complex molecular structures. This paper describes a novel preparation of difficult-to-obtain synthetic intermediates, useful for the total synthesis of certain target compounds. The research was conducted to provide access to suspected pheromones, potentially useful for the biological control of the emerald ash borer and other high priority research objectives. These results are important to scientists especially those in industry, because synthetic pathways must be economical and capable of scale-up in order to be commercially viable.
Technical Abstract: The usual scheme of two-carbon homologation of ketones to 3-methyl unsaturated aldehydes by Horner-Wadsworth-Emmons condensations with phosphonate esters, such as triethyl-2-phosphonoacetate, involves three steps. The phosphonate condensation step results in extension of the carbon chain by two carbons, with an (E) double bond, and a functional group (an ester) is placed on the end of the chain. In the second step, the ester is reduced to an unsaturated alcohol. In the third step, the unsaturated alcohol is partially oxidized to an unsaturated aldehyde. One way to shorten this three step scheme would be to keep the terminal functional group in the oxidation state of an aldehyde, thus obviating the reduction and partial oxidation steps. This was accomplished with the use of diethylmethylformyl-2-phosphonate dimethylhydrazone as the phosphonate reagent. Yields of unsaturated aldehyde products ranged from 74-86%. This new protocol should replace the usual ketone to aldehyde homologation scheme.