Mapping option + left bracket to curly quote

[Jason Alexander]

Since the normal way of typing the curly quotes “ ” and ‘ ’ make no sense to me, I'm trying to create a complex modification that does the following:

     map Option + [ to the single left curly quote

     map Option + ] to the single right curly quote

     map Shift + Option + [ to the double left curly quote

     map Shift + Option + ] to the double right curly quote

According to what I've read online, the following JSON should work, but when I add it to Karabiner, it doesn't work (the default keyboard behaviour continues as before).  Could anyone please advise what I might be doing wrong?

{
  "title": "Option+left bracket to curvy single quote",
  "rules": [
    {
      "description": "Option + left bracket to curvy single quote",
      "manipulators": [
        {
          "type": "basic",
            "from": {
        "key_code": "open_bracket",
        "modifiers": {
            "mandatory": [
            "left_alt"
            ]
        }
            },
            "to": [
        {
            "repeat": true,
            "key_code": "‘"
        }
            ]
        }
      ]
    }
  ]
}