[zq]

Please suggest a procedure for the above transformation.

[Custos]

So you're after a gem-dimethylation next to the carbonyl function on the lactone. I would suggest deprotonation by base (e.g. LDA) followed by alkylation with methyl iodide should work. You could probably do it stepwise but using 2.2 equivs of LDA and MeI might go right to the product.