LINQ. ordered list by key group but first group are with condition

I"m have List ordered by key group.

var productList = CustomerData.Data.Products
                .GroupBy(x => x.CategoryDesc)
                .OrderBy(x => x.Key)
                .ToDictionary(x => x.Key, x => x.ToList());

it's good working

And i want one SPECIFIC group (with sale) set as first in the list.
But the rest of the groups to stay sorted in descending order.
something like that:

***I wrote in the format for the convenience of seeing

[
  {
    "Key": "SPECIFIC",
    "Value": [
      {
        "SubGroup": "wire cutters",
        "Model": "A",
        "Price": "65"
      },
      {
        "SubGroup": "hammers",
        "Model": "B",
        "Price": "71"
      },
      {
        "SubGroup": "hammers",
        "Model": "C",
        "Price": "92.5"
      },
      
    ]
  },
  {
    "Key": "Rank A",
    "Value": [
      {
        "SubGroup": "hammers",
        "Model": "A",
        "Price": "130"
      },
      {
        "SubGroup": "hammers",
        "Model": "B",
        "Price": "142"
      },
      {
        "SubGroup": "hammers",
        "Model": "C",
        "Price": "185"
      },
      
    ]
  },
  {
    "Key": "Rank B",
    "Value": [
      {
        "SubGroup": "pliers",
        "Model": "A",
        "Price": "95"
      },
      {
        "SubGroup": "pliers",
        "Model": "B",
        "Price": "59"
      },
      {
        "SubGroup": "pliers",
        "Model": "C",
        "Price": "65"
      },
      
    ]
  },
  {
    "Key": "Rank C",
    "Value": [
      {
        "SubGroup": "saws",
        "Model": "A",
        "Price": "905"
      },
      {
        "SubGroup": "saws",
        "Model": "B",
        "Price": "589"
      },
      {
        "SubGroup": "saws",
        "Model": "C",
        "Price": "655"
      },
      
    ]
  },
  
]

Add additional Order. First for detecting specific items, ThenBy for the rest.

var productList = CustomerData.Data.Products
    .GroupBy(x => x.CategoryDesc)
    .OrderByDescending(x => x.Key == "SPECIFIC")
    .ThenBy(x => x.Key)
    .ToDictionary(x => x.Key, x => x.ToList());