The reaction given in the problem involves an enolate reacting with an organocopper reagent (Gilman reagent) and then further with an iodomethyl ester to produce the final product [X]. Let's break down the reaction steps:

1. First, the lithium diorganocopper reagent, created from the reaction of an organolithium compound with copper(I) iodide, is highly effective for conjugate addition to α,β-unsaturated carbonyl compounds.
2. The given organocopper reagent will undergo a 1,4- or conjugate addition with the unsaturated carbonyl compound present in the initial substrate.
3. The product of this addition will have the organo group attached to the β-position of the carbonyl compound, while the α,β-unsaturation is eliminated.
4. Next, the reaction proceeds with the vinyl iodide and methyl ester compound in the presence of HMPA, facilitating a coupling reaction that extends the carbon chain by adding the vinyl group to the β-carbon as introduced in the previous step.

Following these steps, of the options given, the major product [X] is:

This option correctly represents the structure wherein the organocopper addition has occurred at the β-position followed by successful coupling at the α-position, resulting in the final compound depicted.