To be honest, I'm not very fond of the completely overlapping primer method for SDM because it frequently results in weird products and everyone ends up trouble-shooting their PCR conditions when the problem is usually the primers themselves.

I usually do something like the attached picture where I design primers around the site facing away from each other like you have, but I don't overlap the primers. Instead I just design them so they're mostly outside the mutation, butting directly up against each other with the desired mutations (outlined in red) on the 5' ends of each primer. Then I order one of the primers phosphorylated. I gel extract the PCR product (you can use DpnI instead, it just might result in slightly more background) and do a blunt end ligation with T4 ligase to circularize the vector. Not overlapping the primers usually results in a very clean PCR product with better amplification and less troubleshooting. I designed those primers based on your desired construct, but double check their sequences if you want to try this, because I copied the sequence you posted by hand and might have made an error.

Some people refer to this as "Round the horn mutagensis" https://openwetware.org/wiki/%27Round-the-horn_site-directed_mutagenesis

which I think is an annoying name, but the article might be helpful.

This is also very close to how NEB's Q5 KLD mutagenesis kit works if you're less comfortable with DIY. https://www.neb.com/en-us/products/e0554-q5-site-directed-mutagenesis-kit

I agree with Alexandra Johnson, using directly adjacent but non-overlapping primers can work very well, that's what I've done in the past.

Some things you can try to get better PCR amplification are:

run multiple small volume (20-25 ul) PCR reactions instead of larger volumes then pool as needed to have enough DNA to ligate and transform

increase the Mg in your reactions

It might be worth trying a different polymerase, I used Vent for this type of work, but Q5 is a good polymerase too (just don't pick something that adds A to the PCR product, been there, done that, oops!)

hope this helps!

I've done this to incorporate an entirely different codon (so 3 nt) as well as changing two nearby codons and it works fine with QuickChange IIXL and correctly designed primers as stated above. Yours appear very short for this. I would add at least 12 (more usually 15) nt on either side of the mutated nt. Oligos are cheap today - make some bigger ones ;-)

I agree with Gary James Hunter your primers are too short put at least 12 to 15 bases on each side of the mutation (try to end the oligos with non-complementary nucleotides ), make only 13 PCR cycles (with 100ng of plasmid template/50ul vinal pcr volume) then treat 1h with dpn1 (1ul=10units) and transform 2ul (no need to make ligation nor to purify the PCR product (sometimes you don't even see it) nor to put phosphate on the oligos...

analyse 3 clones (if you don't have one good clone lower the hybridization temperature..)