Thank you for your help. The most recent attempt gave a very low conversion with much starting material remaining, but I am not sure about the attempt before that. We could double the relative amount of sulfonyl donor in the Knoevenagel, but I think that will only be a marginal improvement.
We tried TBDMS and TBDPS protecting groups previously, and in at least one case, we lost the protecting group on silica. I cannot remember what happened the other time. I am considering going back to the Horner Wadsworth Emmons reaction once I identify a good protecting group. I have a gut feeling that acetyl will not work, but THP has been suggested to me. We have a little time to make this decision as we finish up some other work.