[noorie123]

I am confused about how the last step of this synthesis can be completed?
I have got it this far:
1. Grignard reagent to make alcohol from aldehyde  and add a side chain.
2. H2Cr or PCC to retain ketone back.
3. But how do i get the methyl group on alpha carbon? what reagent does that?

[AWK]

sec-butylmagnesium bromide