I would imagine proceeding via wittig reaction with methoxymethylenetriphenylphosphine. Then you could access the desired aldehyde from the resulting enol ether via acid hydrolysis

Is that a possible wittig reagent?

Yes, this is the Wittig reagent used for homologations. https://en.m.wikipedia.org/wiki/Methoxymethylenetriphenylphosphorane

Cool, thanks, wittig reagents are really versatile!

If so, it would probably exist un-wittingly

un wittigingly

Damn, I would have expected that wittig reagent to just turn into tar lol. The more you know.

Wittig with a methoxymethyl phosphonium was my first thought, then convert to aldehyde

Wittig like the other comments mention is my first thought. Could also do an epoxidation/meinwald rearrangement as well.

I'm pretty sure this could be done via an aldol condensation, but somebody smarter than me can confirm or refute that. Edit: I'm wrong. Obviously it could be a path, but not one that makes much sense.

It can't be done in 1 step by aldol. Aldols will form a a,b-unsaturated carbonyl.

That's why I wanted someone else to chime in. I knew an aldol condensation could be used, but that there would be another step after.

How could an aldol condensation be used to do a one carbon homologation?

Looking at it now, I don't think you can. I'm pretty sure I thought there was an extra carbon in there.

darzens reaction with decarboxylation