Homer-Emmons carbon elongation

The next phase focused on the goal of elaboration of the side chain in the desired sense. The primary alcohol function at C7 was unveiled by hydrogenolysis (Pd(OH)2/EtOAc-MeOH). Oxidation of the resultant compound 13 with chromic oxide pyridine afforded aldehyde 14, which was now to be elongated through some variation of a Homer-Emmons type of reaction. Shortly before tiiese investigations were launched. Still had demonstrated the use of phosphonate 15 as a device to achieve the two-carbon extension of an aldehyde to a Z-enoate (12). Happily, application of the Still method to compound 14 afforded the desired 16, mp 120-121° C, in 80% yield as a 20 1 mixture of Z E enoates. 

The Homer-Wadsworth-Emmons reaction is among the most important reactions for effecting a two-carbon chain elongation of a carbonyl functional group - " It can be described as a general synthetic protocol for the conversion of aldehydes and ketones into aji-unsaturated carbonyl compounds and their derivatives " ... 

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