Programme pour faire passer des colonnes cote à cote, en colonne à la file

Sub e()
dercol = Sheets("a").Cells(2, Columns.Count).End(xlToLeft).Column
derligne = Sheets("a").Range("A" & Rows.Count).End(xlUp).Row
nouvligne = Sheets("b").Range("B" & Rows.Count).End(xlUp).Row + 1
For i = 2 To dercol Step 2
    For j = 3 To derligne
        Sheets("b").Cells(nouvligne, 2).Value = Sheets("a").Cells(j, 1).Value
        Sheets("b").Cells(nouvligne, 3).Value = Sheets("a").Cells(j, i).Value
        Sheets("b").Cells(nouvligne, 4).Value = Sheets("a").Cells(j, i + 1).Value
        nouvligne = nouvligne + 1
    Next
Next
End Sub

Sub test()
Dim i&, LstRw As Long, Arrets As Variant, LstCel As Range
With Sheets("a")
    LstRw = .Cells(Rows.Count, 1).End(xlUp).Row
    Arrets = .Range(.Cells(3, 1), .Cells(LstRw, 1))
    For i = 2 To .Cells(2, Columns.Count).End(xlToLeft).Column Step 2
        Set LstCel = Sheets("b").Cells(Rows.Count, 1).End(xlUp)(2)
        LstCel.Resize(UBound(Arrets, 1), 1) = Arrets
        .Range(.Cells(3, i), .Cells(LstRw, i + 1)).Copy LstCel.Offset(0, 1)
    Next i
End With
End Sub

 Set LstCel = Sheets("b").Cells(Rows.Count, 2).End(xlUp)(2)